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Smallholder dairy cattle production systems in Africa are intensifying production through importation of germplasm from breeding programs conducted in temperate regions to improve commercial cow populations. Presence of genotype by environment interaction results in unfavorable correlated responses. The aim this thesis was to develop strategies for breeding programs in developing countries that can support sustainable intensification of these systems. Specific objectives were (a) to determine desired gains for breeding objective traits, (b) compare progeny testing (PT) and genomic selection (GS) selection strategies, (c) evaluate the economic performance of PT and GS selection strategies and (d) compare genetic gains for economic and non-economic breeding objectives; the Kenya dairy cattle sector was used as a working example. To account for the limited pedigree and performance recording, a five-trait breeding objective and small-sized breeding program were studied. Breeding objective traits, determined based on producer preferences, were milk yield (MY), production lifetime (PLT), calving interval (CI), fat yield (FY) and mature body weight (MBW). Producers were categorized into high intensive group, who placed highest preference on PLT and MY, and low intensity group that placed highest preferences on CI and PLT. MY and FY were the most important traits for processors. Consensus desired gains, based on weighted goal programming, were 2.51, 2.42, 0.22, 0.87 and 0.15% for PLT, MY, CI, FY and MBW, respectively. Comparison of breeding schemes shows that GS schemes had lower accuracies but gave higher responses per year due to shorter generation intervals. Besides genetic gains, economic performance underpins the adoption of selection strategies. GS schemes had between 3.2 and 5.2-fold higher cumulated genetic gain in the commercial cow population and higher gross margins compared to PT schemes. Semen storage made PT schemes more profitable but less so than GS schemes. Functional traits can increase the sustainability of resource poor smallholder systems under harsh environments. Economic breeding objectives yielded undesirable responses in functional traits. Breeding objectives based on desired gains or non-market objectives improved response in functional traits but at a monetary cost. It is concluded that sustainable productivity of smallholder systems can be improved by implementation of local breeding program based on GS, but this requires more emphasis on functional traits, which can be achieved by use of non-economic objectives.

Improved reproductive performance has a substantial benefit for the overall profitability of dairy cattle farming by decreasing insemination and veterinary treatment costs, shortening calving intervals, and lowering the rate of involuntary culling. Unfortunately, the low heritability of classical fertility traits derived from calving and insemination data makes genetic improvement by traditional animal breeding slow. Therefore, there is an interest in finding novel measures of fertility that have a higher heritability or using genomic information to aid genetic selection for fertility. The overall objective of this thesis was to explore the use of milk progesterone (P4) records and genomic information to improve selection for fertility in dairy cows. In a first step, the use of in-line milk progesterone records to define endocrine fertility traits was investigated, and genetic parameters estimated. Several defined endocrine fertility traits were heritable, and showed a reasonable repeatability. Also, the genetic correlation of milk production traits with endocrine fertility traits were considerably lower than the correlations of milk production with classical fertility traits. In the next step 17 quantitative trait loci (QTL) associated with endocrine fertility traits, were identified on Bos taurus autosomes (BTA) 2, 3, 8, 12, 15, 17, 23, and 25 in a genome-wide association study with single nucleotide polymorphisms. Further, fine-mapping of target regions on BTA 2 and 3, identified several associated variants and potential candidate genes underlying endocrine fertility traits. Subsequently, the optimal use of endocrine fertility traits in genomic evaluations was investigated; using empirical and theoretical predictions for single-trait models, I showed that endocrine fertility traits have more predictive ability than classical fertility traits. The accuracy of genomic prediction was also substantially improved when endocrine and classical fertility traits were combined in multi-trait genomic prediction. Finally, using deterministic predictions, the potential accuracy of multi-trait genomic selection when combining a cow training population measured for the endocrine trait commencement of luteal activity (C-LA), with a training population of bulls with daughter observations for a classical fertility trait was investigated. Results showed that for prediction of fertility, there is no benefit of investing in a cow training population when the breeding goal is based on classical fertility traits. However, when considering a more biological breeding goal for fertility like C-LA, accuracy is substantially improved when endocrine traits are available from a limited number of farms.

Sainfoin (Onobrychis viciifolia): a forgotten crop for dairy cows with future potential SUMMARY The world population growth and rising incomes are expected to increase the consumption of animal-derived foods such as meat, eggs and milk. However, livestock production should not only be directed towards increasing productivity but should also incorporate environmental, food safety and animal welfare aspects. Therefore, farm businesses have to respond to the high environment impact of their activities, by using low-input systems including the use of forage legumes. Recent studies have demonstrated that forage legumes with moderate levels of condensed tannins (CT) are beneficial for animal nutrition and animal health. Sainfoin (Onobrychis viciifolia Scop.) is a tanniniferous forage legume containing CT that has potential nutritional and health benefits, i.e. preventing bloating, reducing nematode larval establishment, improving nitrogen (N) utilization and reducing greenhouse gas and N emissions (Chapter 1). However, the use of sainfoin as a fodder crop in dairy cow rations in northwestern Europe is still rather unknown. This thesis investigated the potential of sainfoin in the dairy cow diets and the effect of CT structural properties on rumen fermentation and biohydrogenation (BH). Chapter 2 reports a study where the effect of sainfoin silage on nutrient digestibility, animal performance, energy and N utilization and methane (CH4) production in dairy cows was investigated. Six rumen cannulated, lactating dairy cows were randomly assigned to either a control (CON) or sainfoin based (SAIN) diet. The CON diet was a mixture of grass silage, corn silage, concentrate and linseed. In the SAIN diet, 50% of the grass silage DM in the CON diet was exchanged by sainfoin silage. Total daily dry matter (DM), organic matter (OM) and neutral detergent fiber (NDF) intake did not differ between the two diets. The apparent digestibility of DM, OM, NDF and acid detergent fiber (ADF) were respectively, 5.7, 4.0, 15.7 and 14.8% lower for the SAIN diet. Methane production per kg DM intake was lowest for the SAIN diet and CH4 production as a percentage of gross energy intakes tended to be lower while milk yield was greater for the SAIN diet. Nitrogen intake, N retention and energy retained in body protein were greater for the SAIN than the CON diet. Nitrogen retention as a percentage of N intake tended to be greater for the SAIN diet. These results showed that inclusion of sainfoin silage at the expense of grass silage in dairy cow rations reduced CH4 per kg DM intake. Although nutrient digestibility was decreased, sainfoin silage improved milk production and redirected metabolism towards body protein accretion at the expense of body fat. In Chapter 3, reticular fatty acid (FA) flow and ruminal BH of C18:3n-3 is reported using the reticular sampling technique (Cr-EDTA and Yb-acetate as digesta flow markers) in the lactating cows fed the SAIN and CON diet in Chapter 2. The reticular flows of DM, OM and N were not affected by dietary treatment. However, NDF flow was higher (1.87 vs. 1.40 kg/d) where the cows were fed the SAIN diet. A higher mono-unsaturated FA flow was caused by the higher trans-9-C18:1 and cis-9-C18:1 flow for the SAIN compared to the CON fed cows. The flows of trans-9,trans-12-C18:2 and cis-12,trans-10 C18:2 were higher in the SAIN diet fed cows, but total poly-unsaturated FA flow was not affected by the different diet treatments. The SAIN diet fed cows had a significant lower ruminal BH of cis-9-C18:1 and C18:3n-3, compared to the CON fed cows and tended to a lower ruminal BH in case of cis-9,cis-12-C18:2. These results show that inclusion of sainfoin silage at the expense of grass silage in dairy cow rations reduces ruminal BH of dietary cis-9-C18:1 and C18:3n-3. The effects of replacing grass silage by sainfoin silage in a TMR on milk production and FA in milk fat of the dairy cows in Chapter 2 is reported in Chapter 4. Milk yield reported in Chapter 4 was highest for the SAIN diet with every kg of OM digested of the SAIN diet resulting, on average, in 0.2 kg more milk production. The SAIN diet fed cows had a higher C18:3n-3 and cis-9,cis-12-C18:2 proportion in milk fat compared to the CON diet fed cows. A higher proportion of total trans-C18:1 was found in the cows fed the SAIN diet. There were no differences in proportion of total saturated and unsaturated FA in milk fat between the two diets. Our results showed that replacing grass silage by sainfoin silage improved milk yield and milk FA profile of dairy cows. Effects of the structural properties of CT, i.e. average polymer size (or mean degree of polymerization, mDP); percentage of cis flavan-3-ols (%cis) and percentage of prodelphinidins (%PD) in CT extracts on CH4 production and fermentation characteristics of rumen fluid using an in vitro gas production technique was investigated in Chapter 5. Extracts of CT from eight plants; black currant leaves, goat willow leaves, goat willow twigs, pine bark, red currant leaves, sainfoin plants, weeping willow catkins and white clover flowers were extracted, in order to obtain CT with a wide range in mDP, %PD and %cis. All CT extracts reduced CH4 concentration, decreased the maximum rate of fermentation for CH4 production and rate of substrate degradation. The correlation between CT structure on the one hand and CH4 production and fermentation characteristics on the other hand showed that the %PD within CT had the largest effect on fermentation characteristics, followed by mDP and %cis. Chapter 6 reports results of an in vitro study to investigate the effects of the structural properties CT (mDP, %cis and %PD) on rumen fermentation and BH end-products. The total volatile FA (VFA), ammonia concentration and the proportion of branched chain VFA was reduced in all CT extracts, compared to the control. The proportion of cis-9-C18:1; cis-9,cis-12-C18:2; cis-9,cis-12,cis-15-C18:3 were numerically higher in all CT sources, while the proportion of C18:0 and fractional rate of BH of C18:3n-3 were numerically lower in all CT sources, compared to the control. The correlation between CT structural properties on the one hand and fermentation and BH end-products on the other hand showed that the CT with a high %PD and smaller mDP had the largest effect on fermentation end-products. However, mDP was found to be the most important factor affecting rumen BH. Chapter 7 provides a general synthesis on the major findings of the studies presented in the preceding chapters. In addition, results are reported of a further in vitro as well as an in situ study in which I investigated the mechanisms of CT action in the rumen, in the post-rumen compartments and digestive tract. In the in situ study, fresh sainfoin (Esparcette) was incubated in the rumen and in the abomasum before digested during passage through the digestive tract. For the in vitro study, sainfoin (Ambra) was incubated with rumen fluid buffer for 1, 2, 4, 8, 12, 24 hours. After incubation in situ and in vitro, the incubated material was analyzed for tannin content by butanol-HCl assay. The results showed that the soluble CT dramatically reduced upon introduction in the digestive tract. Additional analyses showed that CT had bound to the fiber and protein (diet and microbes) fractions in the digestive tract. The present work showed that sainfoin silage can be used in dairy cow rations to improve milk production and N utilization and reduce CH4 emissions per kg DM intake. Moreover, sainfoin silage, when replacing part of the grass silage in a TMR of dairy cows, increases ruminal unsaturated FA flow into the reticulum and reduces ruminal BH of dietary cis-9-C18:1 and C18:3n-3. Cows fed sainfoin silage at the expense of grass silage in a TMR increase the proportion of unsaturated FA in milk fat. In terms of condensed tannin structure, mDP and %PD appear to be the most important properties of CT that affect fermentation and BH end-products. Condensed tannins with a mDP ranging from 5 to 10 monomeric units and a %PD > 70.0% seem to have the highest biological activity in the rumen.

Sainfoin (Onobrychis viciifolia): a forgotten crop for dairy cows with future potential SUMMARY The world population growth and rising incomes are expected to increase the consumption of animal-derived foods such as meat, eggs and milk. However, livestock production should not only be directed towards increasing productivity but should also incorporate environmental, food safety and animal welfare aspects. Therefore, farm businesses have to respond to the high environment impact of their activities, by using low-input systems including the use of forage legumes. Recent studies have demonstrated that forage legumes with moderate levels of condensed tannins (CT) are beneficial for animal nutrition and animal health. Sainfoin (Onobrychis viciifolia Scop.) is a tanniniferous forage legume containing CT that has potential nutritional and health benefits, i.e. preventing bloating, reducing nematode larval establishment, improving nitrogen (N) utilization and reducing greenhouse gas and N emissions (Chapter 1). However, the use of sainfoin as a fodder crop in dairy cow rations in northwestern Europe is still rather unknown. This thesis investigated the potential of sainfoin in the dairy cow diets and the effect of CT structural properties on rumen fermentation and biohydrogenation (BH). Chapter 2 reports a study where the effect of sainfoin silage on nutrient digestibility, animal performance, energy and N utilization and methane (CH4) production in dairy cows was investigated. Six rumen cannulated, lactating dairy cows were randomly assigned to either a control (CON) or sainfoin based (SAIN) diet. The CON diet was a mixture of grass silage, corn silage, concentrate and linseed. In the SAIN diet, 50% of the grass silage DM in the CON diet was exchanged by sainfoin silage. Total daily dry matter (DM), organic matter (OM) and neutral detergent fiber (NDF) intake did not differ between the two diets. The apparent digestibility of DM, OM, NDF and acid detergent fiber (ADF) were respectively, 5.7, 4.0, 15.7 and 14.8% lower for the SAIN diet. Methane production per kg DM intake was lowest for the SAIN diet and CH4 production as a percentage of gross energy intakes tended to be lower while milk yield was greater for the SAIN diet. Nitrogen intake, N retention and energy retained in body protein were greater for the SAIN than the CON diet. Nitrogen retention as a percentage of N intake tended to be greater for the SAIN diet. These results showed that inclusion of sainfoin silage at the expense of grass silage in dairy cow rations reduced CH4 per kg DM intake. Although nutrient digestibility was decreased, sainfoin silage improved milk production and redirected metabolism towards body protein accretion at the expense of body fat. In Chapter 3, reticular fatty acid (FA) flow and ruminal BH of C18:3n-3 is reported using the reticular sampling technique (Cr-EDTA and Yb-acetate as digesta flow markers) in the lactating cows fed the SAIN and CON diet in Chapter 2. The reticular flows of DM, OM and N were not affected by dietary treatment. However, NDF flow was higher (1.87 vs. 1.40 kg/d) where the cows were fed the SAIN diet. A higher mono-unsaturated FA flow was caused by the higher trans-9-C18:1 and cis-9-C18:1 flow for the SAIN compared to the CON fed cows. The flows of trans-9,trans-12-C18:2 and cis-12,trans-10 C18:2 were higher in the SAIN diet fed cows, but total poly-unsaturated FA flow was not affected by the different diet treatments. The SAIN diet fed cows had a significant lower ruminal BH of cis-9-C18:1 and C18:3n-3, compared to the CON fed cows and tended to a lower ruminal BH in case of cis-9,cis-12-C18:2. These results show that inclusion of sainfoin silage at the expense of grass silage in dairy cow rations reduces ruminal BH of dietary cis-9-C18:1 and C18:3n-3. The effects of replacing grass silage by sainfoin silage in a TMR on milk production and FA in milk fat of the dairy cows in Chapter 2 is reported in Chapter 4. Milk yield reported in Chapter 4 was highest for the SAIN diet with every kg of OM digested of the SAIN diet resulting, on average, in 0.2 kg more milk production. The SAIN diet fed cows had a higher C18:3n-3 and cis-9,cis-12-C18:2 proportion in milk fat compared to the CON diet fed cows. A higher proportion of total trans-C18:1 was found in the cows fed the SAIN diet. There were no differences in proportion of total saturated and unsaturated FA in milk fat between the two diets. Our results showed that replacing grass silage by sainfoin silage improved milk yield and milk FA profile of dairy cows. Effects of the structural properties of CT, i.e. average polymer size (or mean degree of polymerization, mDP); percentage of cis flavan-3-ols (%cis) and percentage of prodelphinidins (%PD) in CT extracts on CH4 production and fermentation characteristics of rumen fluid using an in vitro gas production technique was investigated in Chapter 5. Extracts of CT from eight plants; black currant leaves, goat willow leaves, goat willow twigs, pine bark, red currant leaves, sainfoin plants, weeping willow catkins and white clover flowers were extracted, in order to obtain CT with a wide range in mDP, %PD and %cis. All CT extracts reduced CH4 concentration, decreased the maximum rate of fermentation for CH4 production and rate of substrate degradation. The correlation between CT structure on the one hand and CH4 production and fermentation characteristics on the other hand showed that the %PD within CT had the largest effect on fermentation characteristics, followed by mDP and %cis. Chapter 6 reports results of an in vitro study to investigate the effects of the structural properties CT (mDP, %cis and %PD) on rumen fermentation and BH end-products. The total volatile FA (VFA), ammonia concentration and the proportion of branched chain VFA was reduced in all CT extracts, compared to the control. The proportion of cis-9-C18:1; cis-9,cis-12-C18:2; cis-9,cis-12,cis-15-C18:3 were numerically higher in all CT sources, while the proportion of C18:0 and fractional rate of BH of C18:3n-3 were numerically lower in all CT sources, compared to the control. The correlation between CT structural properties on the one hand and fermentation and BH end-products on the other hand showed that the CT with a high %PD and smaller mDP had the largest effect on fermentation end-products. However, mDP was found to be the most important factor affecting rumen BH. Chapter 7 provides a general synthesis on the major findings of the studies presented in the preceding chapters. In addition, results are reported of a further in vitro as well as an in situ study in which I investigated the mechanisms of CT action in the rumen, in the post-rumen compartments and digestive tract. In the in situ study, fresh sainfoin (Esparcette) was incubated in the rumen and in the abomasum before digested during passage through the digestive tract. For the in vitro study, sainfoin (Ambra) was incubated with rumen fluid buffer for 1, 2, 4, 8, 12, 24 hours. After incubation in situ and in vitro, the incubated material was analyzed for tannin content by butanol-HCl assay. The results showed that the soluble CT dramatically reduced upon introduction in the digestive tract. Additional analyses showed that CT had bound to the fiber and protein (diet and microbes) fractions in the digestive tract. The present work showed that sainfoin silage can be used in dairy cow rations to improve milk production and N utilization and reduce CH4 emissions per kg DM intake. Moreover, sainfoin silage, when replacing part of the grass silage in a TMR of dairy cows, increases ruminal unsaturated FA flow into the reticulum and reduces ruminal BH of dietary cis-9-C18:1 and C18:3n-3. Cows fed sainfoin silage at the expense of grass silage in a TMR increase the proportion of unsaturated FA in milk fat. In terms of condensed tannin structure, mDP and %PD appear to be the most important properties of CT that affect fermentation and BH end-products. Condensed tannins with a mDP ranging from 5 to 10 monomeric units and a %PD > 70.0% seem to have the highest biological activity in the rumen.

In dit artikel wordt een impressie van de resultaten tot nu toe, het streven de komende jaren en de mening van verschillende deskundigen gegeven.

During the last century in the Netherlands milk production per cow has almost tripled. Accordingly, the amount of concentrates yearly fed per cow strongly increased. Furthermore, automation and robotisation has changed dairy management, especially by the introduction of automatic concentrate feeders and milking systems. A new management concept, emerging in the last decades, is Precision Livestock Farming (PLF). The objective of PLF is to optimize livestock production, by on-line monitoring and control of the production process, utilizing the technical possibilities of automation and robotisation. Nowadays, individual settings for daily concentrate supply and milking frequency are based on standards, ignoring individual variation in milk yield response on concentrate intake and milking frequency. This leads to the main hypothesis for this thesis research that profitability of dairy farming can be improved by utilizing information on individual variation in response. The first objective of this research was to quantify the individual variation in milk yield response to concentrate intake and milking interval length, in order to assess the economic prospects of applying individual optimal settings for concentrate supply and milking frequency. The second objective was the development and testing of adaptive models for on-line estimation of the actual individual response in milk yield to concentrate intake and milking interval length. The conclusion is that on-line estimation of the actual individual response in milk yield and milking duration is possible following a Bayesian approach for time series using an adaptive dynamic model. Besides estimation of the actual response the Bayesian approach adequately detects process deteriorations. Therefore, adaptive dynamic models provide a useful tool for control and monitoring of the dairy production process.

An adequate feed intake is an important prerequisite to realize high milk production in dairy cows, especially during grazing. The analysis of feed intake behaviour can assist in understanding variation in daily intake and in improving its prediction. Indeed, our results indicated that differences in feed intake behaviour were more pronounced when varying the type of roughage than when varying the type of concentrate. Dry matter intake (DMI) was reduced when a ration high in grass silage was fed, but milk production was only numericaly affected. Grazing management might result in increased herbage intake and higher intake of nutrients from herbage by improved nutritional composition of herbage. In the first grazing experiment, herbage DMI was indeed increased when allocating cows daily (1Da) to a new grazing plot compared to every four days (4D) allocation, but only when pasture mass on offer and sward surface height (SSH) were high. Grazing time increased numerically and ruminating time decreased between days in the 4D treatment, coinciding with differences in rumen fermentation characteristics and milk composition. Milk yield was greater in 1Da than in 4D, but milk fatty acid (FA) composition, potentially influencing human health, showed hardly any difference. In a subsequent experiment, herbage DMI was again greater when allocating twice daily (2D) compared to once daily (1Db), especially when SSH was high. Grazing behaviour was more equally distributed in 1Db than in 2D and milk yield was increased in 2D compared to 1Db at high SSH, but as before milk FA composition hardly differed between treatment. The last grazing experiment aimed to take advantage of the higher sugar contents of grass in the afternoon than in the morning. It showed that grazing behaviour and herbage intake were similar between morning (MA) and afternoon allocation (AA), but cows receiving a fresh plot in the afternoon had a longer evening meal than cows receiving a fresh plot in the morning. This, in combination with differences in diurnal chemical composition of the grass between treatments probably caused higher intake of sugars in AA, resulting in a higher milk fat content. However, milk production remained unaffected. In conclusion, the results of this thesis indicate that short-term feed intake behaviour is related to DMI and therefore may be a helpful tool in optimizing DMI and milk production in high-production dairy cows. Increased pasture allocation frequency improves intake and milk yield in grazing dairy cows, especially when offered SSH is high enough. In intensive stripgrazing systems, reallocation of dairy cows following afternoon milking instead of morning milking has no added value.

An adequate feed intake is an important prerequisite to realize high milk production in dairy cows, especially during grazing. The analysis of feed intake behaviour can assist in understanding variation in daily intake and in improving its prediction. Indeed, our results indicated that differences in feed intake behaviour were more pronounced when varying the type of roughage than when varying the type of concentrate. Dry matter intake (DMI) was reduced when a ration high in grass silage was fed, but milk production was only numericaly affected. Grazing management might result in increased herbage intake and higher intake of nutrients from herbage by improved nutritional composition of herbage. In the first grazing experiment, herbage DMI was indeed increased when allocating cows daily (1Da) to a new grazing plot compared to every four days (4D) allocation, but only when pasture mass on offer and sward surface height (SSH) were high. Grazing time increased numerically and ruminating time decreased between days in the 4D treatment, coinciding with differences in rumen fermentation characteristics and milk composition. Milk yield was greater in 1Da than in 4D, but milk fatty acid (FA) composition, potentially influencing human health, showed hardly any difference. In a subsequent experiment, herbage DMI was again greater when allocating twice daily (2D) compared to once daily (1Db), especially when SSH was high. Grazing behaviour was more equally distributed in 1Db than in 2D and milk yield was increased in 2D compared to 1Db at high SSH, but as before milk FA composition hardly differed between treatment. The last grazing experiment aimed to take advantage of the higher sugar contents of grass in the afternoon than in the morning. It showed that grazing behaviour and herbage intake were similar between morning (MA) and afternoon allocation (AA), but cows receiving a fresh plot in the afternoon had a longer evening meal than cows receiving a fresh plot in the morning. This, in combination with differences in diurnal chemical composition of the grass between treatments probably caused higher intake of sugars in AA, resulting in a higher milk fat content. However, milk production remained unaffected. In conclusion, the results of this thesis indicate that short-term feed intake behaviour is related to DMI and therefore may be a helpful tool in optimizing DMI and milk production in high-production dairy cows. Increased pasture allocation frequency improves intake and milk yield in grazing dairy cows, especially when offered SSH is high enough. In intensive stripgrazing systems, reallocation of dairy cows following afternoon milking instead of morning milking has no added value.

Keywords: perennial ryegrass, dairy cows, intake, digestibility milk production, nitrogen utilisation.In the Netherlands, grass is one of the main roughages in the diet of high productive dairy cows. Grass is associated with two main problems: the limited dry matter intake (DMI) and the low N utilisation by dairy cows. Grassland is renovated every 3- 15 years and is usually resown with a mixture of mainly perennial ryegrass cultivars. The aim of the research described in this thesis was to evaluate the effects of perennial ryegrass cultivars on 1) degradation of herbage in the rumen of dairy cows, 2) the DMI, digestibility and milk production by dairy cows, and 3) the N utilisation by dairy cows. These effects were then related to sward characteristics and chemical composition of these cultivars, in order to identify new selection criteria that may be used in grass breeding programmes. Therefore, the effects of eight cultivars in a stall feeding experiment and four cultivars in a grazing experiment on intake, grazing behaviour, digestibility, milk production, milk composition and N utilisation were determined. The perennial ryegrass cultivars consistently differed in their water soluble carbohydrate (WSC) content. Among cultivars, the largest differences were found in WSC content, whereas the differences in crude protein and neutral detergent fibre content were small. An increased WSC content was expected to increase the palatability, and this may increase the intake. However, there was no effect of cultivar on intake in three of the four years of experiments. In one year, the lower intake of two cultivars was associated with a lower WSC content, but also with a severe crown rust infestation. However, the grazing behaviour did not differ among cultivars. The milk production and milk composition were almost not affected by cultivar, with the exception of the year with differences in intake. The cultivars differed only slightly in the degradation characteristics in the rumen. The high crude protein content and the relatively high fractional degradation rate, in comparison with organic matter and neutral detergent fibre, resulted in a high supply of N to rumen microbes. This was expected to be balanced by a higher supply of energy from an increased WSC content. However, the milk urea N content and the N utilisation by dairy cows did almost not differ among cultivars.

Costa Rica, milk production has increased gradually during the twentieth century, in which the activity developed from a non-technical to a technical activity. Together with the evolution of the dairy sector, the incidence of infectious and metabolic diseases increased, leading to increased economic losses. According to a VAMPP data base, the global percentage of abortion during the period between 1988 and 2003 varied between 7.5 and 12%; but at individual farms abortion rates close to 30% occurred in one or more years. Abortion is one of the most important economic disorders.Since the 90´sneosporosis( N.caninum ) has been associated with abortion andfoetallosses in cattle all over the world.In 1996, a study stated (for the first time) the presence ofneosporosisinCosta Ricaand N.caninum was diagnosed (Perez et al., 1998).The aim of this thesis is to describe the most important features ofneosporosisin Costa Rican dairy cattle in order to develop strategies for the prevention and control of the infection. The main results of this thesis are: 1)no significant effects ofNeosporaserostatuswere detected on (re)productive performance; 2) theassociation between management and environmental factors withserostatuswas found to be absent3) in the specific conditions of the dairy herds involved in this study, theserostatusof the cows should be not used as predictor of theserostatusof daughters due to the high probability of horizontal transmission, 4) the killed wholeNeosporacaninumtachyzoitepreparation reducedthe abortion rate in Costa Rican dairy cattle.

Zijn koeien met een hogere melkproductie gezonder of zijn ze juist gevoeliger voor ziekten dan koeien met een gemiddelde productie. Volgens onderzoeker Bonne Beerda van ASG Wageningen UR geeft een hoge melkproductie een negatieve energiebalans en mogelijk extra slijtage. Management is cruciaal voor de gezondheid, ongeacht de fokwaarde. Het fit houden van dieren met een hoge fokwaarde kost wel extra moeite

Zijn koeien met een hogere melkproductie gezonder of zijn ze juist gevoeliger voor ziekten dan koeien met een gemiddelde productie. Volgens onderzoeker Bonne Beerda van ASG Wageningen UR geeft een hoge melkproductie een negatieve energiebalans en mogelijk extra slijtage. Management is cruciaal voor de gezondheid, ongeacht de fokwaarde. Het fit houden van dieren met een hoge fokwaarde kost wel extra moeite

Keywords: perennial ryegrass, dairy cows, intake, digestibility milk production, nitrogen utilisation.In the Netherlands, grass is one of the main roughages in the diet of high productive dairy cows. Grass is associated with two main problems: the limited dry matter intake (DMI) and the low N utilisation by dairy cows. Grassland is renovated every 3- 15 years and is usually resown with a mixture of mainly perennial ryegrass cultivars. The aim of the research described in this thesis was to evaluate the effects of perennial ryegrass cultivars on 1) degradation of herbage in the rumen of dairy cows, 2) the DMI, digestibility and milk production by dairy cows, and 3) the N utilisation by dairy cows. These effects were then related to sward characteristics and chemical composition of these cultivars, in order to identify new selection criteria that may be used in grass breeding programmes. Therefore, the effects of eight cultivars in a stall feeding experiment and four cultivars in a grazing experiment on intake, grazing behaviour, digestibility, milk production, milk composition and N utilisation were determined. The perennial ryegrass cultivars consistently differed in their water soluble carbohydrate (WSC) content. Among cultivars, the largest differences were found in WSC content, whereas the differences in crude protein and neutral detergent fibre content were small. An increased WSC content was expected to increase the palatability, and this may increase the intake. However, there was no effect of cultivar on intake in three of the four years of experiments. In one year, the lower intake of two cultivars was associated with a lower WSC content, but also with a severe crown rust infestation. However, the grazing behaviour did not differ among cultivars. The milk production and milk composition were almost not affected by cultivar, with the exception of the year with differences in intake. The cultivars differed only slightly in the degradation characteristics in the rumen. The high crude protein content and the relatively high fractional degradation rate, in comparison with organic matter and neutral detergent fibre, resulted in a high supply of N to rumen microbes. This was expected to be balanced by a higher supply of energy from an increased WSC content. However, the milk urea N content and the N utilisation by dairy cows did almost not differ among cultivars.

Costa Rica, milk production has increased gradually during the twentieth century, in which the activity developed from a non-technical to a technical activity. Together with the evolution of the dairy sector, the incidence of infectious and metabolic diseases increased, leading to increased economic losses. According to a VAMPP data base, the global percentage of abortion during the period between 1988 and 2003 varied between 7.5 and 12%; but at individual farms abortion rates close to 30% occurred in one or more years. Abortion is one of the most important economic disorders.Since the 90´sneosporosis( N.caninum ) has been associated with abortion andfoetallosses in cattle all over the world.In 1996, a study stated (for the first time) the presence ofneosporosisinCosta Ricaand N.caninum was diagnosed (Perez et al., 1998).The aim of this thesis is to describe the most important features ofneosporosisin Costa Rican dairy cattle in order to develop strategies for the prevention and control of the infection. The main results of this thesis are: 1)no significant effects ofNeosporaserostatuswere detected on (re)productive performance; 2) theassociation between management and environmental factors withserostatuswas found to be absent3) in the specific conditions of the dairy herds involved in this study, theserostatusof the cows should be not used as predictor of theserostatusof daughters due to the high probability of horizontal transmission, 4) the killed wholeNeosporacaninumtachyzoitepreparation reducedthe abortion rate in Costa Rican dairy cattle.

In dairy cattle, the increase in milk yield has been accompanied by a decrease in fertility and a more negative energy balance. As the hormone leptin is involved in regulation of nutritional status and reproductive function (Chapter 2) this is an interesting protein to investigate during the periparturient period in dairy cattle when many changes take place both in energy metabolism and reproductive physiology. The objectives of this study weretoget insight into the function of leptin during the periparturient period and to perform an association study between polymorphisms in the bovine leptin and leptin receptor gene and fertility and production traits.The leptin gene including its promoter region and parts of the leptin receptor gene were sequenced to find polymorphisms,and related to differences in fertility and production traits.Leptin levels were described during the periparturient period in dairy cows and also associations with the genotyped polymorphisms and fertility and production traits were calculated.In Chapter 2 a literature overview regarding leptin and its receptor and their role in metabolic processes and fertility was given. This Chapter also includes recent literature, which was published during the investigations that were described in other Chapters of this thesis.Physiology of LeptinIn Chapter 4 leptin levels during the periparturient period in dairy cows were described and these levels were related to differences in production and reproduction traits. Leptin concentrations in the periparturient cow undergo remarkable changes; leptinconcentrations were high during late pregnancy and declined to a nadir at parturition.The reason of elevated plasma leptin during pregnancy in ruminants seems to be the increase in adipose tissue leptin mRNA due to the lack of a negative feedback (leptin resistance state) and the increase in adiposity. We observed an association of live weight during lactation and prepartum leptin concentrations (Chapter 4) but did not investigate the association between prepartum live weight and leptin concentrations.The reason of the decline in leptin levels towards parturition and during lactation is the mobilization of adipose tissue. Leptin concentrations seem to reflect the state of energy balance during lactation; plasma leptin concentrations were lower in cows with a mean negative energy balance during lactation (Chapter 4).Further analysis indicated that a combination of three polymorphisms located at the leptin promoter region explained 14.3% of the variance in prepartum leptin concentrations. The two extreme combinations with the highest and lowest prepartum leptin concentrations could be used to investigate the function of leptin concentrations in pregnant cows.Genetics of LeptinLeptin influences feed intake, energy balance and fertility and therefore the leptin gene and the leptin receptor gene are possible candidate genes to investigate effects on energy balance and fertility in lactating cows. The leptin gene including its promoter region and parts of the leptin receptor gene were sequenced to find polymorphisms, but also to detect putative transcription factor binding sites on the leptin promoter region. An association study was performed with the found polymorphisms. Associations of allgenotyped polymorphisms with fertility and production traits measured in dairy cows during the periparturient period (Chapters 3 and 7) and alsodifferences in leptin levels between genotypes of all genotyped polymorphisms were analyzed (Chapters 5, 6, and 7).An intronic polymorphism (RFLP1) located on intron 2 of the leptin gene explained a significant part of the variation in milk yield, with differences of 0.5 genetic standard deviation between the two extreme genotypes (Chapter 3). However, because this polymorphism is located at an intronic region and because the polymorphisms found in the exons of the leptin gene were not associated with milk yield, we can not exclude that the causative gene is in linkage disequilibrium with this polymorphism. On the promoter region of the leptin gene SNP -1457 was associated with first postpartum luteal activity ( p =0.017) and with weight loss between week 1 and its minimum weight ( p =0.027), where more weight loss occurred together with a later first postpartum luteal activity.Fertility traits are considered to be important to select for and this SNP could be a potential candidate marker to be informative for fertility in dairy cows. SNP -963 was associated with energy balance ( p =0.015) and dry matterintake(p = 0.030), where a higher dry matter intake occurred together with a higher energy balance (Chapter 7).In order to find an optimal genotype combination with a high milk yield, a good energy balance and fertility some new analysis were performed in Chapter 8. Two genotype combinations of three SNPs were defined in this Chapter and a next experiment and calculations of economical values per trait have to validate if one of these genotype combinations would be a possible candidate to be used in selection.The R4C polymorphism, located at exon 2 of the leptin gene, received a lot of attention by several research groups because of its putative effect on the leptin structure, but several studies, including our study, did not provide convincing evidence that the R4C polymorphism influences the structure and function of leptin. Other studies showed an effect on milk yield in dairy cattle and carcass fat content in beef cattle. On the basis of these results a commercially available R4C-test was developed to improve breeding values in both dairy and beef cattle.Polymorphisms in the leptin and leptin receptor gene have shown to be associated with differences in leptin concentration during late pregnancy (Chapters 5 and 6) but, surprisingly, not during lactation. As the promoter of leptin regulates the expression of leptin, polymorphisms at this region could play an important role in the found differences in plasma leptin levels during late pregnancy. Therefore in Chapter 7 we sequenced the leptin promoter and analyzed the sequence for transcription factor binding sites and polymorphisms. All genotyped polymorphisms were associated with prepartum leptin concentrations but in Chapter 8 we showed that three polymorphisms located on a 135 bp promoter region (282 to 147 bp before the transcription start site) seemed to be important for differences in leptin concentrations during late pregnancy. Also significant differences during the lactation period were found between the two genotype combinations with the highest en lowest leptin concentrations. We proposed a putative pregnancy-dependent enhancer to be located at this site on the leptin promoter.In conclusion, polymorphisms in the leptin gene and its promoter region are associated with traits in dairy cattle like milk yield (RFLP1), energy balance (SNP -963) and fertility (SNP -1457). Further experiments and calculations are needed to investigate if a combination of these three polymorphisms would be useful in future selection. On the promoter region a pregnancy-dependent enhancer might be located. A combination of polymorphisms located at this region might be useful to investigate the function of high leptin levels during pregnancy.

Keywords: Dairy cows, Perennial ryegrass, Rumen fill, Clearance, Degradation, Grazing behaviour.In temperate environments, perennial ryegrass is the most widely used species for feeding dairy cows. That is because of its high productivity, palatability, digestibility and nutritive value. However, perennial ryegrass suffers from two main disadvantages: firstly, its unbalanced nutrient content in terms of crude protein (CP) and energy availability at rumen level and secondly, its low dry matter intake (DMI) by high producing dairy cows. In ruminant animals, DMI is a function of the balance between eating motivation, which is strongly related to palatability, on one hand and rumen capacity on the other. This thesis was divided into three parts: the first part aimed to investigate the possibility of improving pasture DMI by increasing rumen capacity. Rumen capacity is related to the rate of clearance (Kcl) of material from the rumen, which is the summation of both rates of degradation (kd) and passage (kp). Six varieties of perennial ryegrass were screened for their clearance and degradation rates using in vitro , in vivo and in situ techniques. The results suggested that there is a narrow range for selection with respect to clearance and degradation rate. The second part of this thesis aimed at investigating the possibility of improving pasture DMI by improving its palatability. Palatability is mainly a function of flavour and taste, which arise from certain compounds in the grass, especially water-soluble carbohydrates (WSC). High sugar grass varieties were fed to dairy cows in mid lactation. The results showed that feeding high sugar grass did not lead to an improved DMI and milk yield under both stall-feeding and grazing conditions. Moreover, milk composition in terms of fat, protein and lactose, rumen pH, fibre clearance and degradation rates were not influenced. However, rumen ammonia and milk urea concentrations were significantly reduced when feeding high sugar grass. The third part of this thesis aimed to investigate the role rumen fill and fermentation end products may play in signalling the termination of a grazing bout, especially the dusk grazing bout of dairy cows under continuous stocking. It was found that dairy cows interrupted the first two main grazing bouts at the morning and afternoon long before their maximal rumen capacity was reached. Moreover, rumen fill was always maximal at the time when the dusk grazing bout ceased indicating that rumen fill is more likely to play a major role in signalling the termination of the dusk grazing bout.

In dairy cattle, the increase in milk yield has been accompanied by a decrease in fertility and a more negative energy balance. As the hormone leptin is involved in regulation of nutritional status and reproductive function (Chapter 2) this is an interesting protein to investigate during the periparturient period in dairy cattle when many changes take place both in energy metabolism and reproductive physiology. The objectives of this study weretoget insight into the function of leptin during the periparturient period and to perform an association study between polymorphisms in the bovine leptin and leptin receptor gene and fertility and production traits.The leptin gene including its promoter region and parts of the leptin receptor gene were sequenced to find polymorphisms,and related to differences in fertility and production traits.Leptin levels were described during the periparturient period in dairy cows and also associations with the genotyped polymorphisms and fertility and production traits were calculated.In Chapter 2 a literature overview regarding leptin and its receptor and their role in metabolic processes and fertility was given. This Chapter also includes recent literature, which was published during the investigations that were described in other Chapters of this thesis.Physiology of LeptinIn Chapter 4 leptin levels during the periparturient period in dairy cows were described and these levels were related to differences in production and reproduction traits. Leptin concentrations in the periparturient cow undergo remarkable changes; leptinconcentrations were high during late pregnancy and declined to a nadir at parturition.The reason of elevated plasma leptin during pregnancy in ruminants seems to be the increase in adipose tissue leptin mRNA due to the lack of a negative feedback (leptin resistance state) and the increase in adiposity. We observed an association of live weight during lactation and prepartum leptin concentrations (Chapter 4) but did not investigate the association between prepartum live weight and leptin concentrations.The reason of the decline in leptin levels towards parturition and during lactation is the mobilization of adipose tissue. Leptin concentrations seem to reflect the state of energy balance during lactation; plasma leptin concentrations were lower in cows with a mean negative energy balance during lactation (Chapter 4).Further analysis indicated that a combination of three polymorphisms located at the leptin promoter region explained 14.3% of the variance in prepartum leptin concentrations. The two extreme combinations with the highest and lowest prepartum leptin concentrations could be used to investigate the function of leptin concentrations in pregnant cows.Genetics of LeptinLeptin influences feed intake, energy balance and fertility and therefore the leptin gene and the leptin receptor gene are possible candidate genes to investigate effects on energy balance and fertility in lactating cows. The leptin gene including its promoter region and parts of the leptin receptor gene were sequenced to find polymorphisms, but also to detect putative transcription factor binding sites on the leptin promoter region. An association study was performed with the found polymorphisms. Associations of allgenotyped polymorphisms with fertility and production traits measured in dairy cows during the periparturient period (Chapters 3 and 7) and alsodifferences in leptin levels between genotypes of all genotyped polymorphisms were analyzed (Chapters 5, 6, and 7).An intronic polymorphism (RFLP1) located on intron 2 of the leptin gene explained a significant part of the variation in milk yield, with differences of 0.5 genetic standard deviation between the two extreme genotypes (Chapter 3). However, because this polymorphism is located at an intronic region and because the polymorphisms found in the exons of the leptin gene were not associated with milk yield, we can not exclude that the causative gene is in linkage disequilibrium with this polymorphism. On the promoter region of the leptin gene SNP -1457 was associated with first postpartum luteal activity ( p =0.017) and with weight loss between week 1 and its minimum weight ( p =0.027), where more weight loss occurred together with a later first postpartum luteal activity.Fertility traits are considered to be important to select for and this SNP could be a potential candidate marker to be informative for fertility in dairy cows. SNP -963 was associated with energy balance ( p =0.015) and dry matterintake(p = 0.030), where a higher dry matter intake occurred together with a higher energy balance (Chapter 7).In order to find an optimal genotype combination with a high milk yield, a good energy balance and fertility some new analysis were performed in Chapter 8. Two genotype combinations of three SNPs were defined in this Chapter and a next experiment and calculations of economical values per trait have to validate if one of these genotype combinations would be a possible candidate to be used in selection.The R4C polymorphism, located at exon 2 of the leptin gene, received a lot of attention by several research groups because of its putative effect on the leptin structure, but several studies, including our study, did not provide convincing evidence that the R4C polymorphism influences the structure and function of leptin. Other studies showed an effect on milk yield in dairy cattle and carcass fat content in beef cattle. On the basis of these results a commercially available R4C-test was developed to improve breeding values in both dairy and beef cattle.Polymorphisms in the leptin and leptin receptor gene have shown to be associated with differences in leptin concentration during late pregnancy (Chapters 5 and 6) but, surprisingly, not during lactation. As the promoter of leptin regulates the expression of leptin, polymorphisms at this region could play an important role in the found differences in plasma leptin levels during late pregnancy. Therefore in Chapter 7 we sequenced the leptin promoter and analyzed the sequence for transcription factor binding sites and polymorphisms. All genotyped polymorphisms were associated with prepartum leptin concentrations but in Chapter 8 we showed that three polymorphisms located on a 135 bp promoter region (282 to 147 bp before the transcription start site) seemed to be important for differences in leptin concentrations during late pregnancy. Also significant differences during the lactation period were found between the two genotype combinations with the highest en lowest leptin concentrations. We proposed a putative pregnancy-dependent enhancer to be located at this site on the leptin promoter.In conclusion, polymorphisms in the leptin gene and its promoter region are associated with traits in dairy cattle like milk yield (RFLP1), energy balance (SNP -963) and fertility (SNP -1457). Further experiments and calculations are needed to investigate if a combination of these three polymorphisms would be useful in future selection. On the promoter region a pregnancy-dependent enhancer might be located. A combination of polymorphisms located at this region might be useful to investigate the function of high leptin levels during pregnancy.

Keywords: Dairy cows, Perennial ryegrass, Rumen fill, Clearance, Degradation, Grazing behaviour.In temperate environments, perennial ryegrass is the most widely used species for feeding dairy cows. That is because of its high productivity, palatability, digestibility and nutritive value. However, perennial ryegrass suffers from two main disadvantages: firstly, its unbalanced nutrient content in terms of crude protein (CP) and energy availability at rumen level and secondly, its low dry matter intake (DMI) by high producing dairy cows. In ruminant animals, DMI is a function of the balance between eating motivation, which is strongly related to palatability, on one hand and rumen capacity on the other. This thesis was divided into three parts: the first part aimed to investigate the possibility of improving pasture DMI by increasing rumen capacity. Rumen capacity is related to the rate of clearance (Kcl) of material from the rumen, which is the summation of both rates of degradation (kd) and passage (kp). Six varieties of perennial ryegrass were screened for their clearance and degradation rates using in vitro , in vivo and in situ techniques. The results suggested that there is a narrow range for selection with respect to clearance and degradation rate. The second part of this thesis aimed at investigating the possibility of improving pasture DMI by improving its palatability. Palatability is mainly a function of flavour and taste, which arise from certain compounds in the grass, especially water-soluble carbohydrates (WSC). High sugar grass varieties were fed to dairy cows in mid lactation. The results showed that feeding high sugar grass did not lead to an improved DMI and milk yield under both stall-feeding and grazing conditions. Moreover, milk composition in terms of fat, protein and lactose, rumen pH, fibre clearance and degradation rates were not influenced. However, rumen ammonia and milk urea concentrations were significantly reduced when feeding high sugar grass. The third part of this thesis aimed to investigate the role rumen fill and fermentation end products may play in signalling the termination of a grazing bout, especially the dusk grazing bout of dairy cows under continuous stocking. It was found that dairy cows interrupted the first two main grazing bouts at the morning and afternoon long before their maximal rumen capacity was reached. Moreover, rumen fill was always maximal at the time when the dusk grazing bout ceased indicating that rumen fill is more likely to play a major role in signalling the termination of the dusk grazing bout.

Smallholder dairy farmers in the Kenya highlands generally intensify their farming systems by integrating dairy with crop production and shifting from free-grazing to semi-zero- or zero-grazing. They consequently change the breed composition, size and structure of their herds with resultant change in herd demographic rates. The intensification of smallholder dairying has underpinned changes in the farming systems to sustain more intensive land use and support more people per unit area of land in smallholder households. However, the concern is whether smallholders will continue to benefit from dairying through continued intensification when facing the pressures of continuously shrinking landholdings, worsening soil fertility and reduced access to formerly public delivered livestock input and output services, while imported nutrients remain relatively low and non-agricultural job opportunities remain lacking. The objective of this study was therefore to quantify the consequences of the intensification of farming systems in the Kenya highlands on the dynamics of smallholder dairy herds in order to better understand the constraints to, and opportunities for, the continued intensification of smallholder dairying. Data collection was through a random stratified cross-sectional survey of smallholder households. Data from the cross-sectional survey sample were complemented with additional information from longitudinal and targeted semi-structured interviews, which involved a randomly selected sub-sample of the previous cross-sectional survey. The drivers of intensification of smallholder dairying were identified and the relative changes were quantified at the level of the farms and farming systems. Intensification requires increased use of external resources including sources of replacement animals, feed resources, animal health and breeding services and credit to sustain the herd population and production. Prospects for maintaining and expanding smallholder dairying in the Kenya highlands depend upon the proportion of free-grazing farms maintained within the farming systems, because these supply semi-zero- and zero-grazing farms with dairy replacements. The rationale underlying smallholders' breeding decisions is based on multiple objectives of more milk, adaptability to local feed conditions and diseases and the provision of non-marketed production such as manure, insurance and financing roles of cattle. Feeding interventions to support continued intensification of smallholder dairying must be within the context of the household's economy, which is characterised by limited cash flow and low risk bearing capacity. Smallholders need affordable working capital to sustain intensification with use of external resources. Solutions to constraints of intensification must concurrently involve both technical and institutional innovations that may encourage greater complementarities and stratification in the dairy sub-sector.

Uit onderzoek wordt geconcludeerd dat niet helemaal uitmelken van bepaalde kwartieren geen negatieve gevolgen heeft voor de melkproductie. Door lang melken ontstaat er eelt op de speenpunten, door het melkstel eerder af te nemen blijft de schade beperkt

The objective of this thesis was to evaluate genetic aspects of somatic cell count (SCC) in Italian Holstein Friesian population in order to define how to include this trait in selection criteria. Several values of heritabilities were estimated (.06 to -.21) for three parities using different data sets and model of analysis. A model for breeding value estimations of first parity cows was defined and further improvements of the model were discussed. Genetic correlations with production were highly variable in value and sign depending on parity and model of analysis (-.14 to .24). Variation existed between and within lactation and it was concluded that it is important to account for this variation in selection. When a unique value is necessary, a correlations value around zero, indicating a null genetic relationship between production and SCC, should be used. Using an hazard model, it was estimated that an increase in phenotypic level of SCC in Italian Holstein population resulted in higher rate of culling. The approximate genetic correlation between SCC and functional longevity was .31 associating unfavourable values of SCC to poorer longevity. Favourable genetic correlations resulted between udder conformation traits and SCC. A higher udder, strongly attached to the fore abdominal wall, and with short teats was genetically related to smaller values of SCC. Finally an udder health index, including SCC, udder depth, and fore udder attachment was proposed and the inclusion of SCC in the overall selection index was discussed.

Uit onderzoek wordt geconcludeerd dat niet helemaal uitmelken van bepaalde kwartieren geen negatieve gevolgen heeft voor de melkproductie. Door lang melken ontstaat er eelt op de speenpunten, door het melkstel eerder af te nemen blijft de schade beperkt

Smallholder dairy farmers in the Kenya highlands generally intensify their farming systems by integrating dairy with crop production and shifting from free-grazing to semi-zero- or zero-grazing. They consequently change the breed composition, size and structure of their herds with resultant change in herd demographic rates. The intensification of smallholder dairying has underpinned changes in the farming systems to sustain more intensive land use and support more people per unit area of land in smallholder households. However, the concern is whether smallholders will continue to benefit from dairying through continued intensification when facing the pressures of continuously shrinking landholdings, worsening soil fertility and reduced access to formerly public delivered livestock input and output services, while imported nutrients remain relatively low and non-agricultural job opportunities remain lacking. The objective of this study was therefore to quantify the consequences of the intensification of farming systems in the Kenya highlands on the dynamics of smallholder dairy herds in order to better understand the constraints to, and opportunities for, the continued intensification of smallholder dairying. Data collection was through a random stratified cross-sectional survey of smallholder households. Data from the cross-sectional survey sample were complemented with additional information from longitudinal and targeted semi-structured interviews, which involved a randomly selected sub-sample of the previous cross-sectional survey. The drivers of intensification of smallholder dairying were identified and the relative changes were quantified at the level of the farms and farming systems. Intensification requires increased use of external resources including sources of replacement animals, feed resources, animal health and breeding services and credit to sustain the herd population and production. Prospects for maintaining and expanding smallholder dairying in the Kenya highlands depend upon the proportion of free-grazing farms maintained within the farming systems, because these supply semi-zero- and zero-grazing farms with dairy replacements. The rationale underlying smallholders' breeding decisions is based on multiple objectives of more milk, adaptability to local feed conditions and diseases and the provision of non-marketed production such as manure, insurance and financing roles of cattle. Feeding interventions to support continued intensification of smallholder dairying must be within the context of the household's economy, which is characterised by limited cash flow and low risk bearing capacity. Smallholders need affordable working capital to sustain intensification with use of external resources. Solutions to constraints of intensification must concurrently involve both technical and institutional innovations that may encourage greater complementarities and stratification in the dairy sub-sector.

Keywords: heat treatment, maize, barley, starch, protein, in sacco, in vivo, dairy, perennial ryegrass, grazing, supplementation, ruminal fermentation, VFA, rumen, degradability, synchrony.In this thesis the effect of different ways of thermal processing (pelleting, expanding, toasting) of barley and maize on the degradative behaviour of their starch and protein in the rumen of lactating dairy cows are described. In situ studies showed that all thermal processing methods increased the ruminal starch and protein availability of maize, while all thermal processing methods decreased ruminal starch availability but only pelleting increased ruminal protein availability of barley. Based on in vivo experiments compared to untreated grains, expander treatment increased the apparent rumen and total tract digestibility of maize starch but did not affect the digestibility of barley starch. Supplementing grazing dairy cows with pelleted and pressure toasted maize and barley slightly (not significantly) decreased the dry matter intake of grass in the first grazing event in the morning after milking, and it decreased ruminal clearence of nitrogen. Supplementing pasture grass with pelleted and pressure toasted cereal grains decreased the pH, the NH 3 -N level in the rumen, the ammonia to total VFA (TVFA) ratio, the isobutyrate proportion, the acetate to propionate ratio and the non-glucogenic to glucogenic ratio in the rumen. Simultaneously it increased TVFA concentrations, propionate, butyrate and valerate proportions as a percentage of the TVFA. All processed grains did affect production responses in dairy cows, by elevating milk protein and decreasing milk fat production, and milk urea nitrogen but no significant differences between these two heat treatments were found. It is concluded that the need of synchrony is specially important with diets based on fresh grass, in which markedly asynchronous rates of release of energy and nitrogen occur in the rumen. It appears that to generate a better ruminal N and organic matter synchrony to improve microbial N yield and N utilization feeding different types of cereal grain that differ by nature in rate and extent of ruminal degradation has more effect than using one of this processing methods on the same type of grain. Responses obtained from cereal grain supplementation are very dependent on the quality and degradation characteristics of the pasture consumed, which changes through the grazing season.

In de Nederlandse melkveehouderij bestaat grote onduidelijkheid over welk lichtregime geschikt is voor productief en gezond melkvee. Daarbij wordt de behoefte aan duidelijkheid omtrent dit onderwerp steeds groter, mede door een betere benutting van de capaciteit van de melkrobot in de nachtelijke uren. Met dit rapport worden aanbevelingen gedaan t.a.v. het gewenste lichtregime voor melkvee

The objective of this thesis was to evaluate genetic aspects of somatic cell count (SCC) in Italian Holstein Friesian population in order to define how to include this trait in selection criteria. Several values of heritabilities were estimated (.06 to -.21) for three parities using different data sets and model of analysis. A model for breeding value estimations of first parity cows was defined and further improvements of the model were discussed. Genetic correlations with production were highly variable in value and sign depending on parity and model of analysis (-.14 to .24). Variation existed between and within lactation and it was concluded that it is important to account for this variation in selection. When a unique value is necessary, a correlations value around zero, indicating a null genetic relationship between production and SCC, should be used. Using an hazard model, it was estimated that an increase in phenotypic level of SCC in Italian Holstein population resulted in higher rate of culling. The approximate genetic correlation between SCC and functional longevity was .31 associating unfavourable values of SCC to poorer longevity. Favourable genetic correlations resulted between udder conformation traits and SCC. A higher udder, strongly attached to the fore abdominal wall, and with short teats was genetically related to smaller values of SCC. Finally an udder health index, including SCC, udder depth, and fore udder attachment was proposed and the inclusion of SCC in the overall selection index was discussed.

In de Nederlandse melkveehouderij bestaat grote onduidelijkheid over welk lichtregime geschikt is voor productief en gezond melkvee. Daarbij wordt de behoefte aan duidelijkheid omtrent dit onderwerp steeds groter, mede door een betere benutting van de capaciteit van de melkrobot in de nachtelijke uren. Met dit rapport worden aanbevelingen gedaan t.a.v. het gewenste lichtregime voor melkvee

Goed voorbehandelen, een ruimere zuigrustverhouding en vlotter afnemen levert al snel 5 tot 25% kortere machinemelktijden op met een betere speenconditie.

De hoofddoelstelling van het lagekostenbedrijf op de Waiboerhoeve is een kostprijs halen van 34 eurocent per kg melk.

De hoofddoelstelling van het lagekostenbedrijf op de Waiboerhoeve is een kostprijs halen van 34 eurocent per kg melk.

De doelstelling van 34 eurocent is dus niet gehaald.

Goed voorbehandelen, een ruimere zuigrustverhouding en vlotter afnemen levert al snel 5 tot 25% kortere machinemelktijden op met een betere speenconditie.

Uitleg over de opzet van een onderzoek op Nij Bosma Zathe naar de relaties tussen melkproductie, diergezondheid en diermanagement van melkkoeien. Vragen waarop een antwoord gezocht wordt: zijn hoogproductieve melkkoeien meer of minder gevoelig voor gezondheidsproblemen?; vragen koeien die de aanleg hebben om veel melk te geven een aangepast management?; zijn voor een sobere bedrijfsvoering koeien met een lage productieaanleg meer geschikt? In het onderzoek worden vaarzen met een hoge en een lage genetische aanleg voor melkproductie onder vier in de praktijk voorkomende regimes (met verschillende melkfrequentie en verschillende energie-inhoud van het voer) met elkaar vergeleken

In dit artikel wordt een impressie van de resultaten tot nu toe, het streven de komende jaren en de mening van verschillende deskundigen gegeven.

Bovine respiratory disease (BRD) is an important health problem in dairy heifers. BRD causes considerable losses, particularly on farms that experience high levels of the disease. However, an exact quantification of the economic losses due to BRD was not available yet. Despite this lack of economic insight, dairy farmers have to make decisions with regard to prevention of the disease. To make these decisions as economically sound as possible, more accurate insight is necessary into the economic consequences of BRD on the individual dairy farm.The main objective of the research project described in this thesis was to obtain insight into the on-farm economic consequences of BRD in dairy heifers by means of a PC-based simulation model. The second objective was to collect information on the epidemiological consequences of the disease indispensable for model input.The research started with a literature review aimed at obtaining the necessary qualitative and quantitative information on both the effects of BRD on the productivity of dairy heifers and risk factors of the disease. Because relevant literature turned out to be scarce, a formal expert judgement study was held to obtain additional data on the(se) variables of interest.As a next step, a simulation model was developed that calculates the economic losses due to BRD in dairy heifers for individual dairy farm conditions in the Netherlands. Following the results of the expert judgement study, the model distinguishes between two BRD types, being calf pneumonia and a seasonal BRD outbreak.Model calculations showed that for most dairy farms in the Netherlands the economic losses due to BRD will be relatively small: around 1 % of the farm's net return to labour and management for average situations, increasing up to 3-4 % at worst. For individual farms that experience high levels of BRD, the associated losses can be as high as 10-15 % of the farm's net return to labour and management, up to 25 % for large farms. Besides for calculation of the economic losses due to BRD, the model showed also to be useful for evaluation of the on-farm cost-effectiveness of prevention of the disease. Moreover, the model is flexible and user-friendly, hence, can be used as a tool to support decision-making in dairy practice.

In dit artikel wordt een impressie van de resultaten tot nu toe, het streven de komende jaren en de mening van verschillende deskundigen gegeven.

Bovine respiratory disease (BRD) is an important health problem in dairy heifers. BRD causes considerable losses, particularly on farms that experience high levels of the disease. However, an exact quantification of the economic losses due to BRD was not available yet. Despite this lack of economic insight, dairy farmers have to make decisions with regard to prevention of the disease. To make these decisions as economically sound as possible, more accurate insight is necessary into the economic consequences of BRD on the individual dairy farm.The main objective of the research project described in this thesis was to obtain insight into the on-farm economic consequences of BRD in dairy heifers by means of a PC-based simulation model. The second objective was to collect information on the epidemiological consequences of the disease indispensable for model input.The research started with a literature review aimed at obtaining the necessary qualitative and quantitative information on both the effects of BRD on the productivity of dairy heifers and risk factors of the disease. Because relevant literature turned out to be scarce, a formal expert judgement study was held to obtain additional data on the(se) variables of interest.As a next step, a simulation model was developed that calculates the economic losses due to BRD in dairy heifers for individual dairy farm conditions in the Netherlands. Following the results of the expert judgement study, the model distinguishes between two BRD types, being calf pneumonia and a seasonal BRD outbreak.Model calculations showed that for most dairy farms in the Netherlands the economic losses due to BRD will be relatively small: around 1 % of the farm's net return to labour and management for average situations, increasing up to 3-4 % at worst. For individual farms that experience high levels of BRD, the associated losses can be as high as 10-15 % of the farm's net return to labour and management, up to 25 % for large farms. Besides for calculation of the economic losses due to BRD, the model showed also to be useful for evaluation of the on-farm cost-effectiveness of prevention of the disease. Moreover, the model is flexible and user-friendly, hence, can be used as a tool to support decision-making in dairy practice.

Zijn koeien met een hogere melkproductie gezonder of zijn ze juist gevoeliger voor ziekten dan koeien met een gemiddelde productie. Volgens onderzoeker Bonne Beerda van ASG Wageningen UR geeft een hoge melkproductie een negatieve energiebalans en mogelijk extra slijtage. Management is cruciaal voor de gezondheid, ongeacht de fokwaarde. Het fit houden van dieren met een hoge fokwaarde kost wel extra moeite

Uit onderzoek wordt geconcludeerd dat niet helemaal uitmelken van bepaalde kwartieren geen negatieve gevolgen heeft voor de melkproductie. Door lang melken ontstaat er eelt op de speenpunten, door het melkstel eerder af te nemen blijft de schade beperkt

De hoofddoelstelling van het lagekostenbedrijf op de Waiboerhoeve is een kostprijs halen van 34 eurocent per kg melk.

De doelstelling van 34 eurocent is dus niet gehaald.

Uitleg over de opzet van een onderzoek op Nij Bosma Zathe naar de relaties tussen melkproductie, diergezondheid en diermanagement van melkkoeien. Vragen waarop een antwoord gezocht wordt: zijn hoogproductieve melkkoeien meer of minder gevoelig voor gezondheidsproblemen?; vragen koeien die de aanleg hebben om veel melk te geven een aangepast management?; zijn voor een sobere bedrijfsvoering koeien met een lage productieaanleg meer geschikt? In het onderzoek worden vaarzen met een hoge en een lage genetische aanleg voor melkproductie onder vier in de praktijk voorkomende regimes (met verschillende melkfrequentie en verschillende energie-inhoud van het voer) met elkaar vergeleken