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The objective of this study was to analyze the survival patterns of pregnancy outcomes in Egyptian buffaloes under subtropical environmental conditions. The overall reproductive and production indices were performed on a total of 1224 records. The means of days at first AI postpartum, days open and calving interval of Egyptian buffaloes are 62.29, 83.13 and 395.1 days, respectively. The survival analysis of pregnancy outcomes in the present study was restricted to the first AI (576 first AI records). Compared to the low temperature-humidity index (THI), the conception rate (P/AI at 30 days) was significantly decreased at high THI level (OR = 0.45; p = 0.029), however, no significant variations were recorded between the referent (low) THI level and the moderate one (OR = 0.86; p = 0.673). Additionally, the pregnancy loss rate was significantly increased at a high THI level (OR = 2.43; p = 0.008). In comparison with the referent (primiparous) group, the conception rates were significantly increased in the M1 (2–5 parities; OR = 2.84) and M2 (>5 parities; OR = 4.06) multiparous groups (p = 0.007 and 0.004, respectively). The Egyptian buffaloes produce a relatively higher daily milk yield (>9 kg) have significantly lower conception rate compared with the referent (

The calving interval (CI) can potentially impact the economic results of dairy farms. This study highlighted the most profitable CI and innovated by describing this optimum as a function of the feeding system of the farm. On-farm data were used to represent real farm conditions. A total of 1832 accounts of farms recorded from 2007 to 2014 provided economic, technical and feeding information per herd and per year. A multiple correspondence analysis created four feeding groups: extensive, low intensive, intensive and very intensive herds. The gross margin and some of its components were corrected to account for the effect of factors external to the farm, such as the market, biological status, etc. Then the corrected gross margin (cGMc) and its components were modelled by CI parameters in each feeding system by use of GLM. The relationship between cGMc and the proportion of cows with CI

Different breeding strategies targeting two indigenous cattle breeds of Ethiopia (Borana and Horro) were evaluated with the objective of developing appropriate breeding programs that would maximize production and productivity of the breeds maintained on pastures using a deterministic approach. Borana was evaluated for beef, milk and both for beef and milk (dual purpose) while Horro was evaluated for milk and dual purposes. Two units, breeding unit and production unit, consisting of six selection groups were defined for both breeds. Selection criteria used were yearling weight, milk yield, age at first calving, calving interval and calf survival to yearling for dual purpose program and milk yield, age at first calving, calving interval and calf survival to yearling for milk production program. In addition, yearling weight, age at first calving, calving interval and calf survival to yearling were used to improve beef production in Borana breed. Three different levels of breeding bull selection proportions (5%, 10%, and 15%) were used. For all goal traits investigated, more genetic gains were obtained from bull selection groups than the cow selection groups. The bull selection groups also had the shortest generation interval compared to the cow groups (4.07 vs. 6.42 years). From the estimated annual genetic gains for the individual goal traits, all traits had favorable genetic gains except age at first calving. Genetic gains per year were highest for milk yield followed by live weight. Genetic gains were near zero for the other traits. Nearly comparable annual genetic gains were estimated for both Borana and Horro cattle breeds assumed for milk improvement program under different selection proportions. Estimated genetic improvements of about 291.96, 268.63 and 252.73 l of milk were simulated for Borana in 5%, 10% and 15% breeding bull selection proportion. The corresponding improvements for Horro were 291.55, 268.31 and 252.43 l. However, gains were higher in Borana when the two cattle breeds are assumed for dual purpose program (85.92–98.64 for Borana Vs 78.14–90.26 for Horro). Estimated genetic improvements for live weight ranged from 38.96 to 45.11 kg for Borana and 34.17–39.46 kg for Horro when both cattle breeds investigated for dual purpose program. In the current study information is lacking on economic values for each goal trait. Thus, further works are warranted. Except for age at first calving, the genetic gain per year in yearling weight, milk yield, calving interval and survival to yearling obtained from the different options are satisfactory and can result in reasonable genetic improvements of these cattle breeds.

This study aimed to evaluate levels of beef cow fertility using calving interval (CI; measured in days) as a measure, and investigate the effects of breed, season, year and progeny gender on CI. The CI data included 273 764 records collected between 1997 and 2012 and included the seven most common breeds (and their crosses) in Northern Ireland (Charolais, Limousin, Belgian Blue, Simmental, Blonde d’Aquitaine, Aberdeen Angus and Hereford), accounting for 94.1% of beef dams recorded. Mean CI for all cows was 395 days, 30 days longer than the optimum 365 days. Charolais and Belgian Blue dams had the longest CI (P

Retrospective studies were conducted in Kafta-Humera and Wukro areas of Tigray region of Ethiopia. A retrospective study was carried out on 12 herds consisting 2144 Begait cattle from pastoral and agro-pastoral areas to assess herd composition and calf-crop. To evaluate the reproductive performance, 210 cows were selected randomly from pastoral, agro-pastoral, confinement and crop-livestock production systems. All necessary data of reproductive parameters were collected through questionnaire surveys, group discussions and follow-up observations. SPSS software was applied to analyze the data. The result of the present study showed that the average calf-crop of 53% and 42.1% and annual calf mortality rate of 20.8% and 9.4%, were observed for pastoral and agro-pastoral production systems, respectively. The mean age at first service (AFS), age at first calving (AFC) and calving interval (CI) in months were 34.9, 43.9 and 12.9 in pastoral, 35.9, 45.0 and 14.0 in agro-pastoral, 34.4, 44.9 and 15.0 in confinement and 40.5, 49.5 and 19.6 in crop-livestock production systems, respectively. AFC and CI were significantly (P

This study investigated differences between phenotypes of daughters of artificial insemination (AI)-bulls and daughters of natural service (NS)-bulls, respectively, on organic dairy farms in Switzerland. Organic rules recommend the use of natural mating. Therefore it is of interest whether those two groups of phenotypes show different characteristics on organic farms. Only farms using both AI and NS with sires of the same dairy breed as the inseminated cows were included in the study. First lactations of 594 cows from 29 farms were analysed for daily milk yield (DMY), somatic cell score (SCS), and calving interval (CI). Furthermore, veterinary treatments and fat/protein ratios >1.5 and

The aim of this study was to analyse cow reproductive performance on 37 Irish suckler beef farms and determine how reproductive efficiency influences farm profitability. The main reproductive factors associated with gross output value per livestock unit (GO/LU) were average age at first calving (r=−0.19, P

The aim of the present study was to investigate the impact of and variation in both maternal and production input traits on the production economy within extensive and intensive suckler cow production systems. By use of a bio-economic model, feed intake, number of weaned calves, kilogram carcass produced, gross margin and labour costs for an average cow (including offspring) through one production cycle from one calving to the next were simulated. Several scenarios were included, changing the input traits from the average within the third of herds with the lowest performance, to the average within the third of the herds with the highest performance in the Norwegian beef cattle recording system, and compared with baseline scenarios. The results revealed that the variation in production traits had the largest influence on the economic result, but the calf mortality and the calving interval also had considerable economic importance. Both the extensive and intensive production systems were profitable, with a similar gross margin/kilogram carcass.

The bovine abortion surveillance system in France aims to detect as early as possible any resurgence of bovine brucellosis, a disease of which the country has been declared free since 2005. It relies on the mandatory notification and testing of each aborting cow, but under-reporting is high. This research uses a new and simple approach which considers the calving interval (CI) as a “diagnostic test” to determine optimal cut-off point c and estimate diagnostic performance of the CI to identify aborting cows, and herds with multiple abortions (i.e. three or more aborting cows per calving season). The period between two artificial inseminations (AI) was considered as a “gold standard”. During the 2006–2010 calving seasons, the mean optimal CI cut-off point for identifying aborting cows was 691 days for dairy cows and 703 days for beef cows. Depending on the calving season, production type and scale at which c was computed (individual or herd), the average sensitivity of the CI varied from 42.6% to 64.4%; its average specificity from 96.7% to 99.7%; its average positive predictive value from 27.6% to 65.4%; and its average negative predictive value from 98.7% to 99.8%. When applied to the French bovine population as a whole, this indicator identified 2–3% of cows suspected to have aborted, and 10–15% of herds suspected of multiple abortions. The optimal cut-off point and CI performance were consistent over calving seasons. By applying an optimal CI cut-off point to the cattle demographics database, it becomes possible to identify herds with multiple abortions, carry out retrospective investigations to find the cause of these abortions and monitor a posteriori compliance of farmers with their obligation to report abortions for brucellosis surveillance needs. Therefore, the CI could be used as an indicator of abortions to help improve the current mandatory notification surveillance system.

Made available in DSpace on 2018-12-11T17:25:45Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-01-01 The objective of this study was to estimate genetic parameters for carcass traits measured by ultrasound at yearling (Y) and 18 months of age (post-yearling, PY) in order to identify the most appropriate age for the measurement of these traits used for the selection of Nellore beef cattle. In addition, genetic correlations were estimated between these carcass traits and between carcass and other economically important traits such as scrotal circumference, weight, hip height at 18 months of age, age at first calving, and first calving interval (FCI). The carcass traits were longissimus muscle area (LMA), backfat thickness (BF), and rump fat thickness (RF) recorded at two different ages (Y and PY). Gibbs sampling was applied to estimate the genetic parameters using multiple trait animal model. The estimates of posterior heritabilities and standard deviations (SD) for the carcass traits were 0.46, SD=0.06 (LMA_Y), 0.42, SD=0.07 (BF_Y), 0.60, SD=0.09 (RF_Y), 0.33, SD=0.06 (LMA_PY), 0.59, SD=0.08 (BF_PY), and 0.55, SD=0.09 (RF_PY). The genetic parameters obtained in this study suggest the existence of genetic variability in all carcass traits at both ages. Hip height was negatively correlated with BF_PY and RF_PY, indicating that selection of taller animals may lead to animals that will deposit less subcutaneous fat. Selection for growth and carcass traits will not affect FCI, except for an increase in BF_PY which will increase FCI in the long term, possibly due to a correlated response, once the genetic correlation is moderate (0.40, SD= 0.17), and the posterior heritability for FCI was relatively low (0.11, SD= 0.03). The traits LMA, BF and RF measured at Y and at PY are practically the same traits since the genetic correlation are 0.83 (SD= 0.06), 0.94 (SD= 0.02) and 0.72 (SD= 0.07), respectively. In conclusion, ultrasound carcass traits should respond rapidly to selection and can be recorded only in one age, at Y or at PY. Furthermore, there is no need to include the two subcutaneous fat thickness measures (BF and RF) in selection criteria since they are highly genetic correlated. Genetic progress for these carcass traits can be achieved without affecting the breeding value of animals for other economic traits, since the most of genetic correlation estimates are favorable and of low magnitude. Embrapa Southern Region Animal Husbandry, Center of Livestock Research of South Brazilian Fields (CPPSUL) Researcher affiliated with Associação Nacional de Criadores e Pesquisadores Embrapa Cerrados Department of Dairy Science, University of Wisconsin Dow AgroSciences Department of Animal Science, University of California Department of Animal Science, São Paulo State University (UNESP) Department of Animal Science, São Paulo State University (UNESP)

The association of six linear type traits with calving interval, abortions, incidence of stillbirths and pre-weaning losses in Nguni cows in semi-arid and sub-humid communal areas was investigated. It was hypothesised that the odds of a cow having caving interval greater than 1 year, aborting, experiencing stillbirths or losing a calf from calving to weaning decreased with increase in body depth, rump height, flank circumference, chest circumference, navel height and body length. Navel height was measured as the distance from the ground to the lowest point of the cow's belly bottom (navel). Data were collected from a total of 200 Nguni cows from two sites experiencing sub-humid and semi-arid environments (100 each) between May and June 2013. Cows in sub-humid regions were 2.57 times more likely to have a calving interval of 1 year than cows in semi-arid areas. As body depth increased, the number of calves lost by a cow before weaning decreased linearly (p < 0.05) in all parities except parity 4. Cows in semi-arid regions were 2.13 times more likely to lose a calf from calving to weaning. For each unit increase in body depth, the odds of a cow aborting decreased by 1.12 and the odds of a cow having stillbirth decreased by 1.15. Rump height, flank circumference, chest circumference, navel height and body length were not associated with calving interval, abortions, incidence of stillbirths and pre-weaning losses. It was, therefore, concluded that body depth influences calving interval, incidence of stillbirths and abortions in Nguni cows.

The aim of this study was to evaluate the effects of the non-lactating period (NLP) length on the subsequent calving ease and reproductive performance of the purebred Holstein (HO), Brown Swiss (BS) and F 1 crosses (BF) of these breeds. The NLP length was classified into four categories: D 1 : 2 : 45–60d; D 3 : 60–75d; and D 4 : >75d. The lesser incidence of calving difficulty in the purebred HO and BF crossbred cows was recorded at D 3 , with no significant differences with D 2 [11.6% and 9.5%; Crude Odds Ratio (COR)=1.10 and 0.84, respectively]. However, the minimum incidence of calving difficulty in the purebred BS cows was at the same NLP length with significant differences with D 2 (3.8%; COR=0.31). All reproductive indices of the purebred HO cows were less as the NLP length increased. However, lesser estimates of calving interval and days non-pregnant in purebred BS and BF crossbred cows were recorded at longer (D 3 ) NLP (350 and 328d; 112 and 133d, respectively). Purebred HO cows had decreased milk production at extremely short (D 1 ) and long (D 4 ) NLP. Purebred BS cows, however, were more persistent in milk production and had more consistent body condition scores (BCS). In conclusion, shortening the NLP of the purebred HO cows in addition to making minimum changes in diet composition could be an appropriate solution for improving reproduction. Purebred BS and BF crossbred cows were more persistent in milk production and tolerated the diet changes during the NLP.

A 5-year retrospective (from 2008 to 2012) survey was carried out by analyzing data of high producing dairy cows reared in farms located in an area of southern Apennines. The indicators of fertility obtained were related to either season variations or temperature–humidity index (THI). Conceptions were evaluated per month on an annual basis (NCY), i.e., a parameter obtained by subtracting gestation length to the calving date. A significant reduction of NCY was found during the summer months; furthermore, this parameter decreased along with THI increase. The number of heats detected varied similarly to NCY and represented the main cause of lower fertility consequent to heat stress (HS). The age at first calving was not significantly affected by either the season or the THI. The mean number of AI/pregnancy in relation to the calving date was significantly affected by the season but it was not related to THI. The number of days open was significantly larger in the animals calved from January to July than from August to December (163±33 vs 123±36 days; P

There are significant costs associated with reproductive inefficiency in pasture-based dairy herds. This study has quantified the economic effect of a number of key variables associated with reproductive inefficiency in a dairy herd and related them to 6-week calving rate for both cows and heifers. These variables include: increased culling costs, the effects of sub optimum calving dates, increased labour costs and increased artificial insemination (AI) and intervention costs. The Moorepark Dairy Systems Model which is a stochastic budgetary simulation model was used to simulate the overall economic effect at farm level. The effect of change in each of the components was simulated in the model and the costs associated with each component was quantified. An analysis of national data across a 4-year period using the Irish Cattle Breeding Federation database was used to quantify the relationship between the 6-week calving rate of a herd with survivability (%), calving interval (days) and the level of AI usage. The costs associated with increased culling (%), calving date slippage (day), increased AI and intervention costs (0.1 additional inseminations), as well as, increased labour costs (10%) were quantified as €13.68, €3.86, €4.56 and €29.6/cow per year. There was a statistically significant association between the 6-week calving rate and survivability, calving interval and AI usage at farm level. A 1% change in 6-week calving rate was associated with €9.26/cow per annum for cows and €3.51/heifer per annum for heifers. This study does not include the indirect costs such as reduced potential for expansion, increased costs associated with failing to maintain a closed herd as well as the unrealised potential within the herd.

Corrigendum to “Subcutaneous body lipids affect cyclicity and estrus behavior in primiparous Charolais cows”: 10.1016/j.anireprosci.2014.02.014; International audience; Conception rate and the calving interval of beef cows are known to be influenced by body reserves at calving and subsequent postpartum changes. However, few studies have focused on the effect of body reserve dynamics on both postpartum cyclicity and estrus expression. Two successive similar experiments (Year 1: n = 14; Year 2: n = 16) were carried out on primiparous Charolais cows reared indoors during winter to quantify the effects of adipose cell diameter at calving (ACDca) and their postpartum changes (ACDch) on cyclicity and estrus behavior. Cows were managed to calve with a body condition score (BCS, scale 0-5) of 2.5 (Year I) and 1.5 (Year 2). After calving cows were assigned to a Low vs. a High energy level diet until turn out to pasture in May. Within years ACDca was similar between Low and High groups whereas calving to turnout changes of body weight (BW), BCS and adipose cell diameter differed (P < 0.0001). The interval between calving and resumption of luteal activity was negatively correlated with ACDca (P = 0.001). Estrus duration (interval between first and last standing to be mounted (STBM)) was longer in Low than in High groups (P = 0.02). Number of STMB was higher in Low than in High cows. Adipose cell diameter at calving and postpartum changes had distinct effects on the components of reproductive performance; emphasizing the need to consider both amounts and changes of body lipids to predict relationships between nutrition and reproduction in cows.

The effects of first calving (FC) in Holstein heifers on their first lactation, second lactation and lifetime milk production were examined from an initial database of 459 743 animals that first calved between 1 January 1990 and 31 July 2010 in Wallonia, Belgium. The FC age class (18 to 22, 22 to 26, 26 to 30, 30 to 34, 34 to 38 and 38 to 42 months), the FC season and FC year class (1990 to 1994, 1995 to 1999, 2000 to 2004 and 2005 to 2010) were considered when analysing the first and second lactation data. Lifetime data were similarly analysed, but did not include animals that calved after 2005 because many of them were still lactating. Only 24% of animals had their FC before 26 months of age. Animals that first calved between 22 and 26 months of age had more lactations and productive days during their life. They also had higher first and second lactation milk production and lifetime milk production. Summer or autumn FC improved first lactation, second lactation and lifetime milk production, as well as production per day of lactation, compared with winter or spring FC. Compared with animals that calved for the first time in 1990 to 1994, animals with a FC in 2000 to 2004 had a longer calving interval (0.5 months), fewer lactations per animal (-0.6) and fewer days in their lifetime lactation (a reduction of 144 days). As a result, the animals' lifetime production did not increase between 1990 to 1994 and 2000 to 2004, although milk production per day of lactation (22.85 v. 20.49 l/day) and per day of life (11.49 v. 10.78 l/day) improved. Milk fat content was lower in 2000 to 2004 than in 1990 to 1994, but protein content remained relatively constant, probably because of the cows' higher production level and increased dietary concentrate supplementation.

The objectives of the present study were to determine if variance components of calving intervals varied with age at calving and if considering calving intervals as a longitudinal trait would be a useful approach for fertility analysis of Zebu dairy herds. With these purposes, calving records from females born from 1940 to 2006 in a Guzerat dairy subpopulation in Brazil were analyzed. The fixed effects of contemporary groups, formed by year and farm at birth or at calving, and the regressions of age at calving, equivalent inbreeding coefficient and day of the year on the studied traits were considered in the statistical models. In one approach, calving intervals (CI) were analyzed as a single trait, by fitting a statistical model on which both animal and permanent environment effects were adjusted for the effect of age at calving by random regression. In a second approach, a four-trait analysis was conducted, including age at first calving (AFC) and three different female categories for the calving intervals: first calving females; young females (less than 80 months old, but not first calving); or mature females (80 months old or more). Finally, a two-trait analysis was performed, also including AFC and CI, but calving intervals were regarded as a single trait in a repeatability model. Additionally, the ranking of sires was compared among approaches. Calving intervals decreased with age until females were about 80 months old, remaining nearly constant after that age. A quasi-linear increase of 11.5 days on the calving intervals was observed for each 10% increase in the female's equivalent inbreeding coefficient. The heritability of AFC was 0.37. For CI, the genetic-phenotypic variance ratios ranged from 0.064 to 0.141, depending on the approach and on ages at calving. Differences among genetic variance components for calving intervals were observed along the animal's lifetime. Those differences confirmed the longitudinal aspect of that trait, indicating the importance of such consideration when accessing fertility of Zebu dairy females, especially in situations where the available information relies on their calving intervals. Spearman rank correlations among approaches ranged from 0.90 to 0.95, and changes observed in the ranking of sires suggested that the genetic progress of the population could be affected by the approach chosen for the analysis of calving intervals.

The importance of veterinary herd health management (VHHM) is increasing in both dairy farming and veterinary practice. Little is known, however, about how VHHM is perceived by farmers in terms of structure, content and satisfaction. In 2007 a questionnaire, containing questions about these three items was therefore sent to 800 Dutch dairy farmers. Farmers received two questionnaires, one for participants in VHHM and one for non-participants, allowing them to choose the appropriate one. Results were summarized and statistically analyzed. Farmers who were participating in VHHM had better farm performance. They were satisfied with the way VHHM was executed on their farm. However, there were some pressure points. Goal setting and evaluation was still not a regular part of VHHM, even though it is said to be effective in literature. Time spent on VHHM not visible to the farmer was often not charged or not clearly specified on the bill. The differences in opinions between participants and non-participants of VHHM indicated a lack of communication and/or product differentiation. Satisfaction with the way VHHM was executed on the farm had no significant influence on 305-day production. There was, however, some influence on calving interval and bulk milk somatic cell count (BMSCC).

A stochastic simulation model was used to assess the effects of diverse management strategies on beef herds under mountain conditions in the Spanish Pyrenees. Animals grazed on different seasonal resources (valley meadows, forest pastures and mountain pastures) and were fed with forages and concentrates during winter. The simulated management strategies were winter calving (WC, weaning at 180 days), autumn calving (AC, weaning at 160 days), 8-month calving (8MC, weaning at 180 days), and two calvings in 3 years, with weaning taking place at either 170 days of age (2C3Y) or at 9 months (2C3Y9 M). Each strategy was tested for two types of production systems: (i) cow–calf farms that market calves just after weaning; and (ii) cow–calf/finishing farms that fatten the animals by means of an intensive feeding system until achieving a suitable weight for slaughter. A herd of 100 cows was simulated over 15 years, but only data obtained after reaching the steady state (year 6) was used in the analysis. The strategies were evaluated by considering reproductive, productive and economic performance. The percentages of pregnant cows at the end of the mating season were highest for 8MC, 2C3Y and 2C3Y9M (between 92% and 94%). The percentage was intermediate for AC (88%) and lowest for WC (78%), which also showed greater variability between years. The two strategies that extensified management (2C3Y, 2C3Y9M) produced, as expected, a lower number of calves weaned per year (59 and 60), whereas this figure was the highest for 8MC (90). Although AC and 8MC resulted in higher productive performances, the increased labour requirements and winter feeding costs resulted in low economic margins for these strategies, which also meant poorer utilization of natural resources. In economic terms, WC was the best strategy for cow–calf/finishing farms, whereas 2C3Y was the worst of the two types of production systems, although it resulted in the most intense utilization of grazing resources. The long lactating period of 2C3Y9M did not affect the reproductive performance of cows, so this strategy yielded the highest economic margin at weaning. The extensification strategies (2C3Y and 2C3Y9M) were less sensitive to changes in the price of feedstuffs. The information obtained from the simulation of the different strategies is useful for evaluating the possible trade-offs between production, economics, use of natural resources and labour requirements.

The United Kingdom, as in most countries using intensive dairy management programmes, is facing serious challenges in terms of dairy cow fertility, as highlighted by a rapidly increasing calving interval (CI). A mechanistic, mathematical model is described that predicts the size of the future national dairy herd required to supply domestic requirements and its inherent sustainability in terms of production of replacement female numbers. The results from the model suggest that continuing use of current management strategies may result in the national dairy herd being unsustainable due to increasing CI and reduced fertility in as few as 10 years. Adoption of nutritional, endocrine and genetic techniques that increase fertility can effectively and rapidly reverse this trend and reduce the required size of the national herd, thereby reducing methane emissions from dairy production.

Temporal weaning is a common practice to reduce the calving interval. Behavioral responses of calves to short-term separation and subsequent reunion with their mothers were measured. Twenty-seven zebu-type cow-calf pairs were assigned to 1 of 3 groups. Calves in the first group were separated from their dams for 72 hours (FC) using a fence. Calves in this group had some contact with their mothers through the fence. In the second group, calves were removed for 72 hours with no sensorial contact with their mothers (NC). The third group (CO) was used as a control group, in which calves were not separated from their mothers. After the 72-hour period, calves were reunited with their dams. Results show that FC and NC induced significant ( P P P

The objective of this study was to investigate the effect of parity, age at calving, percentage North American Holstein-Friesian and calving date on subsequent calving interval and survival to facilitate the estimation of transition probabilities for month of calving. The economic value of traits that influence calving date, age distribution and survival can be assessed in models using a transition probability matrix. Such a matrix contains the probabilities that a cow of a particular age or breed calving in a particular month will calve in the same, an earlier or later month next year, or be culled. Following editing 1,046,855 calving records in spring-calving herds between the years 1990 and 2004 were analysed. Shorter calving intervals were associated with cows calving later in the calendar year. Age at first calving of

Reproductive efficiency is the primary factor affecting productivity in female buffalo, but is greatly hampered by late attainment of puberty, seasonality of calving, long postpartum anoestrus and subsequent calving interval. Moreover, artificial insemination (AI) is seldom performed because of the weakness of oestrus symptoms and the variability of oestrus length, which makes oestrus detection very difficult. Researchers have tried to cope with each of the critical physiological aspects of buffalo reproductive performance mentioned above. In the present review, the main factors affecting the low reproductive efficiency in buffalo are examined and proposals made for its improvement, taking into account both our research work and literature results. Previous research on the changes in hormone profile during the oestrus cycle and in follicle development were used to develop models for improving reproductive efficiency. Hormonal treatments can be used: (1) to anticipate puberty in order to reduce the age at first calving; (2) to improve fertility in the low breeding season; and (3) to increase the effectiveness of AI programmes by overcoming the difficulty in oestrus detection.

This study was conducted to examine the effect of an extended, 18 months, calving interval (CI) in comparison with a traditional 12 months CI, on milk production and milk composition. In addition, the cows had different milking frequencies (MF), either two or three times per day. This resulted in four treatment groups; referred to as 12-2, 12-3, 18-2 and 18-3. Cows of Swedish Red and White breed were used in the experiment, and the analyses extended over a period of 3 years. Thus, three complete lactations were monitored for cows with 12 months CI and two lactations for cows with 18 months CI, unless the cows were culled during the experiment. The first experimental year, there were 13 cows in each group, and during the second year another five cows were included in each treatment, giving a total of 72 cows for the entire experiment. The achieved calving intervals for the 12 and 18 months CI were 12.2 and 17.5 months, respectively. Cows with 18 months CI had, of course, higher lactation yield, but when the longer lactations were considered there were no differences in milk yield per day of CI. The cows in group 18-3 had higher milk production than 18-2 measured in ECM/day (energy corrected milk) of CI (P

In this paper the genetic relationships between major reproductive traits in beef cattle (Calving Date, Calving Interval and Age at First Calving) and type traits have been estimated to evaluate the usefulness of type classification in predicting reproductive performance in beef cattle. We estimated favourable genetic correlations between Calving Interval and type traits ranging from −0.027 to −0.297. However, type traits and Calving Date appear to be genetically independent and the genetic relationships between Age at First Calving and type traits are, in general, non-favourable. Genetic correlations between type traits and Calving Date ranged from 0.0 to –0.125. Genetic correlations between Age at First Calving and Final Score, Body Depth and Tight Development were, respectively, 0.399, 0.445 and 0.447. Our results suggest that the possibility of using type classification to construct an index to improve reproductive performance is little. The more reliable possibility to build a possible selection index comprising type classification and reproductive performance would be based on Age at First Calving. Type classification at first calving could help to increase the information to select dams to stay on the farm in subsequent calvings on the basis of their expected performance.

Data on 132 lactation records pertaining to 51 Anatolian buffaloes maintained at Kocatepe Agricultural Research Institute, Afyon, Turkey were analyzed to study the effects of different non-genetic factors on day at peak yield, peak yield (maximum daily yield), 305-day yield, persistency and calving interval. The persistency of lactation was estimated by three methods: P 1 , the ratio of 305-day yield to maximum daily yield; P 2 , the coefficient of variation (%) among daily yields in successive days, and P 3 , the average of proportions of each month’s milk yield to preceding month’s milk yield after the peak is attained. The overall means of day at peak yield, peak yield, 305-day yield, P 1 , P 2 , P 3 persistency measures, and calving interval were 55.12±3.22 days, 7.30±0.15 kg, 894.17±19.55 kg, 120.56±1.72, 34.99±1.07%, 85.22±0.92% and 441.97±7.93 days, respectively. The 305-day yield was significantly ( P P P 1 and P 3 . The regression on lactation length was found significant ( P P 1 , P 2 , P 3 and calving interval were 0.037±0.091, 0.279±0.104, 0.437±0.099, 0.027±0.09, 0.008±0.088, 0.154±0.100 and 0.134±0.10, respectively.

Dairy farms in southern Norway were surveyed to obtain information regarding reproduction management in tied herds. A total of 1613 farms were included in the analyses. Reproductive performance during the main breeding period of the year (November 1 to February 28) was measured using the following dependent variables: calving to first service and last service interval, number of artificial inseminations per cow, non-return rate at 60 days, and calving interval. Culling for failure to conceive was found to be associated with longer calving to first service interval, more inseminations per cow and lower non-return rate. More inseminations per cow and lower non-return rate were also recorded in herds where breeding was close to calving. Oestrous checks late in the evening and frequent observations were associated with shorter calving to last service interval and shorter calving interval. Calving to last service interval was prolonged if the farmers were occupied with routine work while conducting oestrous checks. Manual rectal pregnancy testing was of little importance for reproductive efficiency in dairy herds with good breeding performance. More inseminations per cow occurred in herds where oestrous checks were conducted systematically 3 and 6 weeks after service. Calving to last service interval and calving interval were shorter when only one person was responsible for the herd breeding management.

A field study was carried out on 38 dairy farms in the Netherlands to determine the relationship between mastitis and fertility management with 305-day milk production and gross margin. Questionnaires were used to get insight into the farmers' management. Out of 150 variables related to mastitis and fertility management, and technical and economic results, 44 variables were selected based on correlation of ≥0.25 or ≤−0.25 with milk production and/or gross margin. These variables were used in two separate partial least-squares (PLS) analyses. PLS has the advantage that it can handle a large number of variables in relation to the number of cases. The PLS-model of 305-day milk production had R2 = 0.54 and showed a positive relation between 305-day milk production and awareness of the farmer regarding bulk somatic-cell count (BSCC), the goal level of the farmer for BSCC, and hygiene of the milking parlour. Fertility was negatively related to 305-day milk production, in spite of a relatively good fertility management on high-producing farms. R2 = 0.46 for gross margin. The aspiration level of fertility did not seem to affect gross margin, but awareness of BSCC and calving interval (CI) had positive effects. Such awareness seemed a general parameter for good economic results, because it was correlated with different aspects of gross margin.

Calving interval is currently used as the measure of reproductive performance in South Africa and many other countries, but some authors have claimed that calving interval is not a suitable measure of reproductive performance, when cows are mated during a restricted breeding season. Numerous authors have suggested that calving date is a suitable alternative measure of reproductive performance. This study was undertaken to investigate the factors influencing calving interval and calving date, in order to determine their suitability as measures of reproductive performance under conditions of restricted breeding. Two models were developed, each having the following independent effects: Year of birth, age of dam, previous sex of calf, previous calf birth weight, previous calf weaning weight and previous calving date. A number of interactions were included. In Model 2, gestation length was included as an additional independent effect. The dependent variables were: calving interval and calving date. Year of birth and previous calving date had a highly significant influence on calving interval and calving date whilst age of dam had a highly significant influence on calving interval and a significant influence on calving date. A 1 day delay in previous calving date, resulted in a 0.72 day decrease in calving interval, and a 0.27 day increase in calving date (Model 1). In Model 1, previous calving date was the variable having the greatest influence on calving interval and calving date with previous calving date having a much greater influence on calving interval than on calving date, as determined by the significantly larger mean square associated with calving interval than calving date. When calving interval was corrected for the large negative effect of previous calving date, calving interval and calving date became similar measures. It was concluded that calving interval was a more biased method of evaluating reproductive performance than calving date, when cows are mated during a restricted breeding season, due to the negative relationship between previous calving date and calving interval and that calving date could be a suitable alternative measure of reproductive performance.

Genetic parameters for age at first calving (AFC) and calving interval (CI) for zebu cows grazed on semi-arid pasture in Ceara State, Brazil, were estimated by Restricted Maximum Likelihood (REML). The animal model utilized included the fixed effects: year of birth of cow, herd, month and year of calving with respect to AFC, and additionally, month and year of calving preceding CI. Means were 59.0 months and 577.4 days for AFC and CI, respectively. Heritability estimates for AFC and CI were 0.29±0.09 and 0.14±0.01, respectively. Repeatability estimate for CI was 0.15±0.01. Genetic and phenotypic correlations between traits were 0.10 and 0.43, respectively.

Because a well-controlled calving interval in dairy cattle improves the profits of the farmer, it is significant to develop an efficient oestrus detection system. Therefore, a fuzzy inference system has been developed as a management tool. It uses signals, correlated with physiological and behavioural effects like changes in activity, milk yield and milk temperature. A Controlled Random optimisation method is used to tune the membership function shapes. Using routinely collected data, the system proves to detect cows in heat with acceptable results.

A total of 57 buffalo cows were divided into two groups and subjected to different intensities of oestrous detection. In the first group (G1), oestrus was checked at 6-h intervals, four times daily starting at 0600 h as compared to twice daily in the second group (G2) at 0800 h and 1500 h. The year was also divided into two seasons: cool from November to April; and hot from May to October. Ovulatory activity was monitored by measuring progesterone concentrations in blood serum. Samples were obtained every 3 or 4 days post-partum until conception was confirmed. More frequent detection practices produced shorter intervals for all of the reproductive parameters. Calving interval was less for cows in G1 in the cool season (363.5 +/- 16.0 vs. 400.3 +/- 14.3 days) than in the host season (387.0 +/- 15.3 vs. 441.5 +/- 14.3 days). Oestrous detection efficiency was higher (P0.01) in G1 in both seasons. Season of calving produced a significant effect (P0.05) on the number of services per conception. The cool season calvers had better reproductive performance than cows calved during the hot season.

The objective of this study was to investigate a reproductive management strategy that optimized profitability per cow per day of productive life when bovine somatotropin (bST) was used. Nine herds were involved with a portion of animals randomly assigned to one of four treatments: breeding at first oestrus after 60 days in milk (DIM, 13.2-month calving interval (CI)); breeding at first oestrus after 150 days in milk (16.5-month calving interval); first lactation animals never re-bred; and second lactation animals never re-bred. All herdmates not assigned to the study served as controls. All treatment animals received bST commencing at 63 days after parturition. Effects of bST supplementation with delayed pregnancy and without pregnancy were determined using the Test Day Model© (TDM). Results indicated that with bST use a 16.5-month calving interval increased (P

Few investigations have been performed where effects of a planned increase of the calving interval have been elucidated. In order to study these matters, a research project has started at the Swedish University of Agricultural Sciences (SLU). The study involves researchers both at the Agricultural and Veterinary Faculties at SLU as well as from the dairy industry in Sweden. Experiments are being performed within two experimental herds (approximately 150 cows) belonging to SLU. We are now in the middle of a three-year study comparing 12- and 15-month calving intervals (herd 1) or 12- and 18-month calving intervals (herd 2). In herd 2, two milking frequencies (2 vs. 3 per day) are combined with the two calving intervals. Long-term effects on health, reproduction, milk production (including milk quality) and production efficiency are studied in detail. The plan is to study individual cows in three consecutive years. Interactions with management system and breed will also be investigated. Results from the first lactation show no significant differences in fertility between treatments. So far, milking three times per day has not given a more persistent lactation compared with milking two times a day. Some cases of salty taste of milk have been noticed.

Of 314 calvings, there were 67 (21.4%) abnormally terminated pregnancies (ATP), 37 of which were abortions, 19 stillbirths and 11 premature calvings. Forty-nine cows with ATP were matched to normally calving herd mates and their milk production data and fertility indices were compared. The ATP were associated with complete failure of lactation in 21 (42%) cases and with short lactation lengths of less than 200 days in nine (18.3%) cases. Lactation in the remaining 19 (38.7%) cows was characterized by a low lactation yield of 2318 ± 211 kg and lactation length 296 ± 13 days. Corresponding parameters for the control herd mates were 3250 ± 190 kg and 314 ± 12 days, respectively. The number of days to first service services per conception and calving interval cows with ATP were 139 ± 17 days, 2.29 ± 0.15 and 465 ± 23,days, respectively. Corresponding fertility indices in the control group were 107 ± 9 days, 1.83 |+- 4.18 and 407 ± 12 days, respectively. Also 11 of 49 (22.3%) cows, with ATP were culled because of infertility witcompared with only five (10.2%) in the controls. Twenty-six other cows with ATP were randomly difided into two groups. In Group 1, 14 cows were treated with 100 ml of 6% colloidal iodine (Merckojod®, Bayer, Leverkusen, Germany), 40–50 days after calving followed by a prostaglandin F2α analogue (Estrumate®, ICI, Cheshire, UK) 20 days later. In Group 2, 12 cows were left untreated and served as a control. Treatment reduced the interval to First service by 63 days and the calving interval by 79 days and it increased services per conception by 0.38. No culling was recorded from this group. ATP not only denied a calf to the farm but also reduced milk production. Intrauterine administration of colloidal iodine coupled with PGF2α could bring ATP animals to near normal fertility.

F1 Sahiwal × Friesian crossbreds imported from Australia (SF × AU) and New Zealand (SF × NZ) were compared with locally bred F1 Friesian × Local Indian Dairy (FL), F1 Friesian × improved Local Indian Dairy (FS). 39.1, 39.6, 8.5 and 14.2% of the SF × AU, SF × NZ, FL and FS heifers respectively produced more than 2000 kg of milk in the first lactation. Proportions of animals that lactated for more than 250 days were 60.3, 73.2, 37.7 and 43.0 per cent respectively. Least-squares means for total first lactation yield were 1428.6, 1425, 1033.9 and 1225.0 kg respectively; for index traits yield per day calving interval and yield per day from birth to second calving were 3.16, 3.13, 2.77 and 3.10 kg and 0.898, 0.933, 0.753 and 0.885 kg respectively. There were no significant differences between SF × AU and SF × NZ in milk yield and reproduction. They were superior to the locally bred crosses in total milk yield. However differences between all the crossbreds were not significant for the index traits. FL and FS crosses produced their calf more than two months before the imported crossbreds. Reproductive traits based on only successful calvings can however be biased.

Abstract. The hypothesis that maternal condition can affect the sex ratio of offspring was investigated by examining the sex of calves born to mature female humpback whales, Megaptera novoeangliae, in the southern Gulf of Maine. Maternal condition was inferred from calving interval: females calving at intervals of 3 or more years were judged to be in 'superior' condition, while those calving at the modal 2-year interval were considered to be in 'average' condition, and those at an interval of 1 year in 'poor' condition. The sex ratio of calves horn to females in superior condition deviated significantly from the expected 1:1 (χ2 = 8·05, N = 21, df = 1, P 0·7). Interpretation of these results according to the Trivers & Willard (1973, Science, 179, 90-92) hypothesis would suggest that mature female humpbacks in superior body condition bias their reproduction towards the sex (males) with the greater variance in reproductive success, although rejection of the central assumption of this study (that a longer calving interval results in superior maternal condition) would render such an interpretation invalid.

Compared with the intensive research into the effects of short term variation of feeding the dairy cow, that into multi-lactation feeding is very modest. The evidence is conflicting regarding cumulative beneficial effects on milk production from a single increment in plane of nutrition repeated lactation by lactation: some experiments do, others do not, show a positive build-up of milk production over at least a double lactation. The general concensus of evidence is that liveweight stabilizes at a level commensurate with plane of nutrition but interpretations differ regarding the course of liveweight change over successive lactations of underfeeding. Evidence is uniform on residual effects on resumption of normal intakes after a lactation of underfeeding: milk yield is reduced for a lactation and body reserves are re-established. This effect constitutes a change in partition of nutrients between milk and body, a change that is in fact initiated in the later phases of the lactation of underfeeding itself. Neither diet composition in ad lib. feeding regimes nor system of allocation of compound feeds with ad lib. forage allowance had specific multi-lactation effects. Variation in rations applied over multiple lactations did not produce definitive effects on milk composition beyond those observed in the short term, and did not affect calving interval; but some health disorders were associated with protracted intensive feeding.

In Trial I, Brahman cows (n=132) and first-calf heifers (n=63) were randomly allotted to one of the following groups: controls (n=65); to receive 2 minutes of gentle uterine manipulation per rectum one time between 29 and 35 days after calving (n=67); or to receive uterine manipulation at weekly intervals from 9 through 51 days after calving (n=63). In Trial II, eight mature cows out of each treatment were bled at 30 minute intervals from −60 to 180 minutes relative to the time of uterine manipulation. Uterine manipulation was performed after Time 0. Treatment did not affect (P>0.1) pregnancy rate in first-calf heifers. However, treatment did affect pregnancy rate in mature cows (P< 0.01) with weekly uterine manipulation being lower (60.5%) than that of the control (83.7%) and the one uterine manipulation groups (89.1%). Conception rate at first estrus after calving was also affected by treatment (P< 0.01) in mature cows, with the weekly uterine manipulation group being lower (3.3%) than the control (30.3%) and the one uterine manipulation groups (36.4%). The proportion of cows conceiving early (by 85 days after calving) was higher (P< 0.01) in the one uterine manipulation group (87.8%) than the control (58.3) or the weekly uterine manipulation groups (57.7%). Mean plasma PGFM (pg/ml) was higher (P< 0.01) on Day 9 (450.5 ± 15.8) than on Day 16 (244 ± 15.8), Day 23 (185.1 ± 15.8), Day 30 (203.1 ± 15.8), Day 37 (198.7 ± 17.3), Day 44 (191.6 ± 18.9) and Day 51 (132.4 ± 24). Mean plasma PGFM (pg/ml) was lower (P< 0.09) in the weekly uterine manipulation group (103.3 ± 29.2) than the one uterine manipulation (216 ± 29.2) and control groups (276.6 ± 31.6). Proportions of the prepalpation PGFM mean were not affected by treatment on Day 9, 16 37, 44 or 52 but were higher (P< 0.06) for the weekly uterine manipulation (Day 23) and one uterine manipulation group (Day 30) groups when compared with the control group. One uterine manipulation was effective in increasing fertility in mature cows. Uterine manipulation at weekly intervals decreased fertility in mature cows. One uterine manipulation increased the proportion of mature cows with a 365 day calving interval by 29.5% over the controls. Per rectum palpation of the postpartum cow can cause release of PGF2α.

The reproductive problems of crossbred cattle in four dairy farms were studied in 1988 and 1989. The mean calving intervals were 445.4 ± 4.6, 544.9 ± 7.7, 435.2 ± 4.2 and 495.5 ± 10.0 days in the four farms. There were significant (P < 0.05) differences between calving intervals of different farms. Parity at two farms, and season and year of calving at one increased significantly (P < 0.05) the calving interval. The mean number of services per conception ranged from 1.60 ± 0.85 to 2.33 ± 1.04 at the four farms with significant (P < 0.05) differences between farms. Season of conception increased significantly (P < 0.05) services per conception at two farms. Observed cases of abortion ranged from 1.7 to 20.2%. There were significant effects of parity (P < 0.01) and season (P < 0.05) on abortion at two farms.

A total of 694 calving records of 582 N'Dama cows (aged 4–15 years) was classified into three groups for comparison of ability to calve again within 21 months postpartum, and calving interval. The classification was based on body weight changes between 1 and 4 months postpartum, as follows: Group 1 (n = 208), cows that lost more than 5% of their initial postpartum weight during this period; Group 2 (n = 352), cows that maintained body weight during this period; Group 3 (n = 134), cows that gained more than 5% of their initial postpartum weight during this period. Both criteria of reproductive performance differed significantly (P Analysis of body weights from 4 months before conception to the month of conception showed that 71 % of cows were gaining weight at a mean rate of 1.74 kg per month before conception. The magnitude of rate of gain depended on the calendar month (i.e. season) in which the 3 month preonception period began. The target body weight for conception in these N'Dama cows is about 220 kg. These results indicate that strategic supplementation of cows during the first 3 months after parturition either to maintain or to gain weight could lead to improved reproductive performance in village-managed animals.

Return to postpartum ovarian activity was monitored in two groups of Ethiopian Bos indicus (Zebu) cows whose calves were either weaned at 4.5 months (Group 1, n = 19) or 7.5 months (Group 2, n = 27). Mean (±SE) postpartum anoestrous interval (PPAI) was 188.4 ±9.6 days and differed significantly between groups (124.4 ±7.3 vs. 241.2 ± 9.3 days, respectively; P P

Data on 4123 inseminations from 1237 Ethiopian Arsi (Bos indicus) cows were analysed. Data were obtained from the Gobe ranch of the Ethiopian Ministry of Agriculture where cows were kept under similar management. Calving and postpartum anoestrous intervals averaged 620.9 ± 3.8 (SEM) and 304.1 ± 3.5 days respectively and were affected by year of calving and parity (P < 0.001). Mean service period was 58.6 ± 2.7 days and influenced by season of first oestrus (P < 0.05). Calving interval was significantly (P < 0.001) correlated with the duration of postpartum anoestrus (r = 0.93) and length of service period (r = 0.12) but there was no significant relationship between postpartum anoestrous interval and service period duration. Only 1.6% of cows calved annually, 31.6% calved after 13–18 months, 45.6% between 19 and 24 months, and 21.2% calved over 24 months. About 47.5% of cows conceived on first service, 29.3, 21.0, 1.7 and 0.4% conceived after two to five services, respectively. Mean interval between services was 53.0 ± 39.7 days and number of services per conception averaged 1.8 ± 0.8. Gestation length was 280.5 ± 3.3 days. It was concluded that long postpartum anoestrus, poor oestrus detection and low conception rates contributed to extending calving intervals.

A 3-yr study was conducted to evaluate different methods of inducing beef cows to cycle and successfully breed earlier in the breeding season. Three hundred beef cows nursing their calves were allocated to groups to be treated with Estrumate or Syncro-Mate-B or to serve as untreated controls. Half of the calves in each group were weaned for 48 h prior to the start of the breeding season. The 48-h weaning group had a significantly higher proportion of animals with calving intervals of less than 365 d (P

Data collected at Chobela Research Station, Mozambique, were used to compare Nguni and Africander cattle for beef production. The traits studied were weight of calf at weaning (210 days) and at 18 months (540 days), weight of cow at calving and at weaning, and calving interval. Productivity was expressed as weight of calf per year per unit metabolic weight of cow. Africander calves were heavier than Nguni calves both at weaning (12%) and at 18 months of age (8%). Growth rates from weaning to 18 months were similar in the two breeds. Africander cows were heavier than Nguni cows both at calving (20%) and at weaning (16%). Calving intervals were shorter in Nguni than in Africander (418 and 460 days, respectively). Nguni had higher overall productivity than Africander (11–15%). This superiority was mainly due to their shorter calving interval (i.e. higher calving rate).

0.23 (0.14) 0.24 (0.14) 0.13 (0.16) Fat yield 0.32 (0.14) 0.39 (0.13)* 0.23 (0.15) Protein yield 0.16 (0.15) 0.32 (0.14) 0.06 (0.16) Somatic cell score -0.34 (0.14)* -0.11 (0.15) -0.14 (0.17) Calving interval -0.07 (0.18) 0.00 (0.22) -0.18 (0.30) Survival -0.08 (0.22) -0.17 (0.23) -0.62 (0.22)* Body condition score 0.36 (0.14)* *Genetic correlations significantly different from zero. Conclusions This is the first study to estimate genetic correlations between susceptibility to M. bovis infection and performance. The results from this study suggest that selection for increased survival may indirectly reduce, while selection for reduced SCS and increased fat production and BCS may increase susceptibility to M. bovis infection within the national Holstein Friesian dairy herd. However, future work on independent data that corroborates these finding is required before definitive conclusions can be drawn.

Data pertaining to records of 1,274 calving intervals for 400 breeding buffaloes maintained at the Livestock Experiment Station, Qadirabad, District Sahiwal (Pakistan), were analyzed to investigate the magnitude of influence of month and season of calving on the length of subsequent calving interval. The longest average calving interval of 609.9 days was recorded for buffaloes calving in January, while the shortest average calving interval of 502.8 days was observed for those calving in June, the difference being highly significant (P < 0.01). When the data were split in accordance with season of calving, the calving intervals for buffaloes calving in winter, spring, summer and autumn averaged 569.1, 570.6, 506.6 and 515.7 days, respectively. The differences between intervals for winter and spring calvings and between intervals for summer and autumn calvings were non-significant. All other differences were highly significant (P < 0.01). Thus, in most of the buffaloes calving in winter or spring, the first post-partum oestrus and conception are delayed till the following autumn or winter, resulting in significantly longer calving intervals. In contrast, animals calving in summer or autumn exhibit post-partum heat and conception during autumn or winter, resulting in shorter calving intervals.

In view of the expense in time and money of collecting complete lactation records of energy yield and food intake and hence efficiency (yield/intake), the accuracy of using part-lactation measures of energy yield, food intake and efficiency were examined. Data were from 150 British Friesians and 71 British Jerseys, which had milk-energy yields recorded once weekly, and cumulate individual ad libitum intake of a complete pelleted diet recorded every 14 days, throughout the calving interval. A number of part-lactation measures of efficiency were examined which allow the relative accuracy of different combinations of partial measures to be approximately determined. Measurements taken near mid-lactation gave the best predictions of total lactation milk-energy yield, food intake and efficiency. The more information collected, the greater the accuracy of prediction, but at diminishing returns on effort. The use of the ratio of a single observation of energy yield (1 day's yield) and food intake (14 day's intake) predicted lactation efficiency more accurately than recording energy yield throughout the whole lactation. For a given time spent recording intake, splitting the period of recording into 2 periods, separated by 8 weeks, proved more accurate than a single period. Short periods of recording could provide useful predictions of yield, intake and efficiency, giving potential benefits in reduced costs and earlier availability of information.

The present contribution is a review of earlier studies on genetic aspects of bull fertility as measured by non-return rate when used for AI. The conclusions may be summarised as follows. 1. (1) Conception rate and calving interval are determined by the fertility of the bull and the fertility of the cow jointly. One unit of genetic improvement in male fertility is therefore of equal importance to one unit of improvement in female fertility. 2. (2) The heritability of bull fertility, as measured by the non-return rates from a few hundred inseminations, is large enough to provide a basis for efficient selection. The genetic standard deviation is, however, considerably less for male than for female fertility. 3. (3) The genetic correlation between male and female fertility is slight, and the same holds true for the genetic correlation between male fertility and milk production. 4. (4) In the final selection of progeny-tested bulls, due attention should be given to the estimated breeding value of the bull with respect to male fertility as well as to female fertility.