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Research conducted over recent decades to improve understanding of the functional responses among sward characteristics, intake rate and grazing behaviour has been reviewed. The opportunities to modify grazing pattern by changes in feeding management are discussed and the implications for dairy-farm feeding strategies are highlighted. Progress in the understanding of the functional responses between sward characteristics and intake rate and their main components (bite mass, bite area, bite depth and bite rates) has been substantial. However, progress in understanding the factors that mediate the initiation and the end of individual meals has been poorer and requires further study. Much of the research has been conducted using short-term experiments with a limited number of experimental animals and mostly conducted on mono-specific uniform swards. The physiological state of the animal as well as the maintenance energy associated with grazing strategies have received very little, if any, attention. More integrated (sward, animal, management) and long-term basic research is required to improve feeding practices at the farm level and the design of farms for the new generation of grassland-based dairy-production systems. The results of studies examining interactions between sward state, grazing behaviour and intake are reviewed, and their validity and application in commercial dairy herds to improve feeding management are discussed. The shortcomings of such research are examined with a view to identifying future research strategies required for future grassland-based dairy enterprises. [ABSTRACT FROM AUTHOR]

Abstract: Effects of daily herbage allowance (DHA) on milk production and composition, body condition score (BCS) and grazing behavior of primiparous Holstein cows during early lactation were investigated. Cows were blocked by body weight (BW), age and BCS, and randomly assigned within block to one of three grazing treatments (n =11 cows each) being: high (HA, 30kg DM/cow/d), medium (MA, 15kg DM/cow/d) and low (LA, 7.5kg DM/cow/d) DHA. Cows were grazed in 8 consecutive grazing paddocks (GP) of 7d of occupation each. The experiment was a completely randomized block design and data were analyzed as repeated measurement in time. Milk production was higher in HA and MA groups than in LA (24.3 and 22.7 vs. 19.2L, P<0.01 respectively). Milk response to extra DHA was 0.43L of milk/kg DHA between LA and MA treatments, which dropped to 0.19L of milk/kg between LA and HA treatments. Cows in the HA treatment had higher BCS than cows in MA and LA treatments (3.18 vs. 3.05 and 3.07; P<0.05). Cows on all treatments mobilized BCS during the first 3 weeks after calving but, while HA cows lost ∼0.5 points of BCS, LA cows lost 1 point. The probability of a cow grazing at any time increased (P<0.01) as the experiment progressed, being 54.5, 61.3, 66.8 and 68.7min/100min for GP 3, 5, 7 and 8, respectively. Probability of grazing increased linearly for cows receiving HA (0.39min/100min/d) and MA (0.44min/100min/d) treatments at higher rate than cows receiving LA (0.22min/100min/d) treatment. A linear effect of days in milk (DIM) on bite rate as well as an interaction of DIM by treatment occurred. At DIM=0, the mean value for bite rate was ∼15bites/min, and the slope relative to DIM was higher for HA and MA cows (0.54 and 0.69bites/min/d, respectively) than for LA cows (0.29bites/min/d). The result of the present experiment evidence the major role of DHA on milk production in primiparous dairy cows during early lactation, being more important at lower levels of DHA. The lack of response on milk production to higher levels of DHA might have been related to the low effective grazing time and bite rate exhibited by early lactation grazing primiparous cows. [Copyright &y& Elsevier]

Abstract: A simulation rumen model has been developed to function under non-steady state conditions in order to allow prediction of nutrient availability in dairy cows managed under discontinuous feeding systems. The model simulates availability of glycogenic, aminogenic and lipogenic nutrients to lactating dairy cows fed discontinuously. The model structure considers input of up to three different feeds fed independently at any time during the day. Feeds are described by their nitrogen (N), carbohydrate and fatty acid fractions. The N containing feed fractions include ruminally undegraded crude protein (CP), ruminally insoluble but potentially degradable CP, ruminally soluble CP and ammonia N. The feed carbohydrate fractions include ruminally undegradable neutral detergent fibre (NDF), ruminally degradable NDF, ruminally insoluble starch, ruminally soluble starch and sugars. The fatty acids in the feeds are divided between long chain fatty acids and volatile fatty acids (VFA). Additionally four pools were defined representing absorption of amino acids, glucose, long chain fatty acids and volatile fatty acids. The rumen microbial population is represented as a single pool. Besides a flexible structure, new features to the extant model include adoption of the concept of chewing efficiency (or chewing effectiveness) during eating, variable fractional ruminal absorption rates of VFA and variable fractional ruminal degradation rates of NDF as a function of rumen liquid pH, as well as a variable rumen volume which directly affects rumen concentrations of metabolites. The model continuously (i.e., by minute) predicts release of soluble components from the feeds in the rumen, concentration and absorption of fermentation end products in the rumen, rumen pools of nutrients and microbial biomass dynamics, as well as passage of microbial biomass and non-fermented nutrients from the rumen, in response to various feeding strategies. Model evaluation covered a wide range of feeding strategies that included pasture and housed feeding systems. Overall, the mean square prediction error (MSPE) as a percentage of the observed mean was relatively low (<10%) with a high amount of the total variation explained by random variation (>65%). Deviation from unity varied between 23% (rumen dry matter content) and 25% (NDF), indicating some consistent over and/or under prediction. A more detailed evaluation was done based on studies available that reported diurnal behaviour of key model outputs such as rumen pools, rumen pH, and rumen VFA. The predictions broadly simulated the observed values quantitatively, relative to general diurnal patterns, and relative to differences between treatments in the predicted diurnal patterns. Results show that the model provides a tool to assess potential outcomes of changing feeding strategies which may be particularly valuable in assessing selection of feeds, amounts and times of the day to offer the feeds. The continuous nature of the simulated output also allows determination of the time(s) of the day that ruminal (and/or post-ruminal) delivery of nutrients may limit ruminal output of nutrients (and/or availability of nutrients) to support milk nutrient synthesis. [Copyright &y& Elsevier]

Context: The increasing intensification of pasture-based systems has subjected the cows to different productive environments, which could affect physiological responses and, consequently, their productive performance. Aims: The aim was to determine the effect of contrasting housing facilities (outdoor soil-bedded vs compost-bedded pack barn) used in partial confinement in pasture-based systems, on the metabolic adaptation during early lactation and its impact on productive and reproductive performance of autumn- and spring-calving dairy cows, having as a positive control a zero-grazing confined system in compost barn. Methods: Multiparous Holstein dairy cows that calved in autumn (n = 36) and spring (n = 48) were distributed in the following three treatments from calving to 90 days in milk (DIM): outdoor soil-bedded–grazing (OD-GRZ), compost barn–grazing (CB-GRZ), compost barn–total mixed ration (CB-TMR). Milk production, total milksolids (TMS), body condition score, non-esterified fatty acids (NEFA), beta-hydroxybutyrate (BHB), cholesterol, insulin, insulin-like growth factor-1 (IGF-1), and the proportion of cows with corpus luteum were determined in repeated measurements. Key results: In both calving seasons, milk production and TMS yields did not differ between OD-GRZ and CB-GRZ, but were greater in CB-TMR (P < 0.0001). In autumn, NEFA and BHB were not affected by treatments, but cholesterol increased faster in CB-TMR (P = 0.0500). In spring, NEFA and cholesterol concentrations were not affected by treatment, but BHB remained greater in OD-GRZ until 90 DIM than in the other treatments. IGF-1 and insulin did not differ between treatments in autumn, but in spring, IGF-1 was greater in CB-TMR (P < 0.0001). The proportion of cows with corpus luteum was not different between pasture-based treatments, but both were greater than CB-TMR up to 40 DIM in autumn (P = 0.0489) and during the entire study in spring CB-TMR (P = 0.0285). Conclusions: Although no differences were found among housing facilities in partial confinement, except that in spring OD-GRZ cows had greater BHB concentrations, confined cows prioritised milk production instead of reproductive function, despite presenting better energy indicators than did pasture-based cows. Implications: Outdoor housing combined with grazing can increase the risk of greater BHB concentrations, indicative of subclinical ketosis, under heat-stress conditions, when compared with indoor housing. Confined cows increased milk production but had a delay in the resumption of ovarian cyclicity, even having a better energy status than pasture-based cows. The intensification of pasture-based dairy systems subjects the cows to different productive environments. This work evaluated whether metabolic, productive, and reproductive variables were affected by two contrasting facilities used in partial confinement (outdoor soil-bedded vs compost barn) plus grazing and a total confinement system in autumn- and spring-calving cows. Spring outdoor soil-bedded cows presented subclinical ketosis even after 30 days postpartum, possibly being associated with heat stress. Confined cows presented greater milk production but a delayed resumption of ovarian cyclicity. [ABSTRACT FROM AUTHOR]

Abstract The effect of length of the allowed grazing time (Experiment 1), length of starvation time and placement in the rumen of inert bulk material before grazing (Experiment 2) on liquid and particulate rumen pool sizes, composition and fermentability was investigated. In Experiment 1, four lengths of allowed grazing time (1.00, 1.75, 2.50 and 3.25 h) after overnight starvation were compared. The allowed grazing time had no significant effect on total and liquid rumen pool sizes after grazing but did affect (P < 0.05) dry-matter (DM) and organic matter (OM) rumen pool sizes. The non-significant diferences between the volatile fatty acid (VFA) rumen pool sizes before and after 1 h of grazing may indicate a delay in the availability of the more rapidly fermentable substrate for the microorganisms. The total VFA remen pool sizes increased significantly (P < 0.01) with the allowed grazing time, which suggests that these fermentation products may be involved in the control of the grazing time in later stages during the day. Experiment 2 consisted of a factorial combination of two lengths of starvation before grazing (16.5 and 2.5 h) and the presence or absence in the rummen of 12.5 kg of a synthetic indigestible material. The duration of starvation before grazing did not affect significantly the particulate, ammonia and VFA rumen pool sizes after grazing except for propionic acid, which was reduced (P < 0.09) by the longer starvation time. The inclusion of inert bulk material in the rumen before grazing significantly reduced (P < 0.05) the total, Liquid DM, OM, and ammonia rumen pool sizes but not the VFA rumen pool sizes after grazing. High levels of ammonia as well as total rumen contents may be involved in the control of the grazing time in this experiment. [ABSTRACT FROM AUTHOR]

Volatility of markets and climate are driving exporting dairy industries to increase milk production from pasture. However, some regions are not able to grow due to economic, social and environmental constraints. The objective of this study was to analyse at the farm system level the opportunities and challenges for the growth of pasture-based dairy production in Uruguay. A national database of 256 dairy farms was used to compare four groups of Uruguayan farms selected according to the total milk production growth rate from 2013 to 2017. Their productivity (milk production per hectare) and profit was compared by fitting mixed models. Complementarily, the International Farm Comparison Network database was used to compare biophysical and economic indicators of typical farm systems of Argentina, Australia, Ireland, Holland, New Zealand, United States and Uruguay from 2013 to 2017. The growing groups of farms (medium and high growth; >5% per year) showed more productivity due to their higher stocking rate and achieved a higher margin over feed cost and a lower feeding cost per L of milk than the shrinking groups (medium and high decrease; <0% per year). The growing systems showed a higher consumption per hectare of home-grown forage (pasture and conserved forage) and supplements. Margin over feed cost decreased alongside milk price over the time frame analysed, with no significant interaction between group and year. Productivity in New Zealand, Australia, United States and Holland was above 10,000 L/ha whereas in Ireland, Argentina and Uruguay it was below 7000 L/ha. Consumption of home-grown forage per hectare in the former countries more than doubled the latter, which consumed approximately half the potential forage production locally reported. Home-grown forage consumption per hectare was a more likely driver of productivity than bought-in feed or feed conversion efficiency. Uruguay achieved the lowest cost of production however current low stocking rates (0.7 cows/ha for the typical farm system) limit home-grown forage consumption and productivity growth. Inter-annual variation in economic performance was larger than the variation in biophysical performance for all countries. This study showed that pasture-based farming systems in Uruguay could make a leap in milk production without losing competitiveness by doubling their home-grown forage consumption through increased stocking rates. For such growth, some future challenges will remain around managing P accumulation and runoff in intensifying farms as well as improving farm design and infrastructure to attract labour, improve its productivity and assure animal welfare. • Growing farms consumed more home-grown forage and produced more milk per hectare. • Growing farms achieved higher feed margin and lower feeding cost per litre of milk. • Uruguay achieved the lowest cost of production of the exporting countries compared. • Holland, US, NZ and Australia double Uruguay in home-grown forage consumption. • Low stocking rates in Uruguay, Argentina and Ireland limit productivity and growth. [ABSTRACT FROM AUTHOR]

Pasture persistence is a key determinant of the economic and environmental performance of pastoral animal production systems. Large and deep root systems that help resist summer water stress have been proposed as a relevant trait for vegetative persistence of perennial temperate forage species growing in subtropical climates or under future climatically challenging scenarios. In a previous study [Jauregui et al., 2017. Persistence of tall fescue in a subtropical environment: Tiller survival over summer in response to flowering control and nitrogen supply. Grass and Forage Science72, 454–466] we have shown that nitrogen fertilization and grazing management aimed at 'control flowering' increased the survival of tall fescue tillers during harsh summers in Uruguay (lat. 32°S). Here we assessed: (i) to what extent tiller survival is mediated by root system size in spring and (ii) what consequences tiller survival entails for root mass, depth and morphology the following autumn. In two field experiments, significant increases in tiller survival in response to nitrogen fertilization and grazing management (+60% and +80% in 2011/12 and 2012/13, respectively) were not related to concomitant effects on the size or depth of the root system in spring (p >.10). Even when six‐fold within‐treatment variation in root mass was observed, within‐treatment variation in summer tiller survival was little affected (<15%, p =.08). In turn, differences in tiller survival over summer affected little root system characteristics the following autumn. Therefore, we found scant support for the hypothesis that large and deep root systems contribute to survival of tall fescue tillers in this subtropical humid climate. Except for soils with less than 30 mm of plant available water holding capacity, summer water deficits did not induce severe tiller mortality in tall fescue in this climate. [ABSTRACT FROM AUTHOR]

The integration of feeding behaviour with hepatic and endocrine–metabolic signals provides insights for a better understanding of short-term intake in dairy pasture-based systems. Therefore, the objective was to quantify hepatic and endocrine–metabolic signals before and after the first daily feeding event relating to feeding behaviour in a total mixed ration (TMR) versus a grazing pasture-based diet. During 15 days of adaptation and 5 days of measurements, 14 multiparous Holstein cows (days in milk = 148 ± 12.7; liveweight = 535 ± 10.9 kg; body condition score = 2.8 ± 0.08 (1–5 scale); milk yield = 28.9 ± 3.32 kg) were assigned to two treatments in a randomised block design: PAS = pasture (herbage allowance = 45 kgDM/cow.day; dry matter (DM) = 21%, net energy requirements for maintenance and lactation = 6.7 MJ/kgDM) + concentrate (0.9% of liveweight) or TMR (55 : 45 forage : concentrate ratio, as-dry basis; DM = 40%, net energy requirements for maintenance and lactation = 7.2 MJ/kgDM) ad libitum in a free stall facility. The DM intake of the first feeding event, feeding behaviour, and total DM intake and milk production, were measured. Blood and liver samples were taken before and after the first feeding event for hormones and metabolites determination. Comparing TMR versus PAS cows, total DM and net energy requirements for maintenance and lactation intake, milk production, and energy balance were greater (P < 0.05), eating and rumination activities were lower (9.2%, P < 0.01; 2.4%, P = 0.06 respectively) and resting activity was greater (11.6%, P < 0.01), whereas duration and DM intake of the first feeding event did not differ. The insulin : glucagon ratio and liver adenosine triphosphate : adenosine diphosphate ratio increased (P < 0.05), and plasma glucose decreased (P < 0.05) after the first feeding event only in TMR cows, probably due to greater flux of propionate to the liver. A negative correlation between post-feeding liver adenosine triphosphate : adenosine diphosphate ratio and post-feeding liver acetyl coenzyme A (r = –0.82, P = 0.045) was also observed only in TMR cows. It is concluded that hepatic and metabolic signals known to support the hepatic oxidation theory in TMR-fed cows appear not to affect the cessation of the first feeding event in mid-lactation cows grazing a pasture-based diet. Further research is required to relate intake rate, flux of nutrients to liver and its response in hepatic metabolism in grazing dairy cows. In pasture-based dairy systems, dry matter herbage intake is the major limitation of milk production, so it is very important to know the signals that regulate herbage intake. An unknown question is the role of liver signals in short-term feed intake regulation, particularly in grazing dairy cows. We have discovered that hepatic oxidation does not have a primary role in the cessation of one of the most important feeding events at grazing – the first feeding event. [ABSTRACT FROM AUTHOR]

High production pasture-based dairy systems have difficulty meeting cows' nutritional and environmental needs, especially during extreme environmental conditions during summer in temperate zones. The mixed systems combine pasture access with supplementation periods to achieve the maximum use of pastoral conditions and help better meet nutritional requirements. The aim of this study was to determine if the different conditions during confinement (compost barn, CB vs. outdoor soil-bedded, OD) affect behavioral, biochemical and physiological indicators of welfare in dairy cows. Multiparous Holstein cows were randomly assigned to one of two groups for confinement periods: a compost barn (CB, n = 15): consisting of compost bedding, a roofed area, ventilation and sprinklers, and an outdoor soil-bedded area during (OD, n = 15), which had a soil floor and shaded area. The frequency of eating, ruminating, drinking, lying, standing, and walking behavior in confinement was evaluated for three months during summer. Rumination minutes was recorded with collars automatically throughout the day. Blood samples were taken to determine total proteins, albumin, globulins and creatine kinase. The subcutaneous temperature was recorded during December and January (n = 7 per group). During the confinement, the CB cows spent more time lying down (P = 0.001) and ruminating (P = 0.04) than the OD cows. During pasture access, the CB cows spent more time grazing (P = 0.003) and less time ruminating (P < 0.0001) than the OD cows. Furthermore, the CB cows had lower subcutaneous temperature than the OD cows during the day (P < 0.0001). Serum creatine kinase concentrations tended to be higher (approximately 360 % more) in the OD cows than in the CB cows (P = 0.07). Differences in the type of confinement determined behavioral changes during both the confinement and pasture access, demonstrating the adaptability of cows to a varied environment. In conclusion, the different conditions during confinement affected the welfare indicators of the dairy cows in the mixed system during summer, with OD cows experiencing poorer welfare than CB cows, based on behavioral, biochemical and physiological indicators of welfare. • Different confinement conditions affected the welfare indicators of cows in mixed feeding systems. • Welfare status of compost barn cows was better than outdoor soil-bedded cows. • Compost barn cows were lying more during confinement than outdoor soil-bedded cows • In pasture, outdoor soil-bedded cows were lying more than compost barn cows, compensating for the confinement behavior. • Outdoor soil-bedded cows had higher subcutaneous temperature than compost barn [ABSTRACT FROM AUTHOR]

Summary: Milk fatty acid (FA) profiles were determined in Holstein cows (n = 27) fed total mixed rations (TMR) ad libitum (G0) or diet composed by TMR (50% dry matter [DM] offered) plus grazing of pasture with 6 hr of access time to paddock in one session (G1) or 9 hr in two sessions (G2) at 45 days in milk (DIM). Moreover, milk FA was determined at 65 DIM when G0 cows turned out to G1 diet without adaptation period (Post‐G0), G1 remained as controls. Milk FA was quantified using gas chromatography and mass spectrometry. Preformed FA at 45 DIM was greater (+27%) for G2 than G0 cows (p < .05). Stearic acid (C18:0) was 30% greater for G2 cows (p < .05). De novo FA was lowest for G2 cows (p < .05). Conjugated linoleic acid (CLA) did not differ (p < .12), while vaccenic acid (C18:1trans) was twofold greater for grazing treatments (p < .01). Linolenic acid [C18:3(n‐3)] was greatest for G2 and lowest for G0 cows (p < .01). Omega 6 FA was greater for G0 than grazing cows, mainly due to linoleic acid [18:2cis(n‐6); p < .05]. These results determined that n‐6/n‐3 ratio was almost threefold greater for G0 than grazing cows (p < .001). When diet of G0 cows changed to include pasture (Post‐G0), preformed FA increased (p < .05), explained mainly by the increase (p < .05) of stearic (C18:0) and C18:1trans, while de novo FA tended to decrease (p < .1). Moreover, the amount of CLA and C18:3(n‐3) tended to increase (p < .1) in Post‐G0 cows. Offering 50% of dietary DM from pasture modified milk FA profile in early lactation potentially beneficial for human health. When TMR‐fed cows were turned out to 50% pasture, milk FA profile reflected dietary change without need of an adaptation period. [ABSTRACT FROM AUTHOR]

Contents The study postulated that differential nutritional management during the early lactation period would be reflected in endometrial expression of genes related to embryo growth at the end of the voluntary waiting period. Thus, the effect of the combined use of total mixed ration ( TMR) and grazing under different herbage allowances during the first 75 days post-partum ( DPP) on endometrial gene expression was evaluated in primiparous dairy cows. Cows were blocked by body weight, age and body condition score and randomly assigned to three grazing treatments: high ( HA, 30 kg DM per cow per day), medium ( MA, 15 kg DM per cow per day) and low ( LA, 7.5 kg DM per cow per day) herbage allowance (mixed pasture, 2,600 kg DM per ha) plus 8 kg DM of supplement or TMR (55% forage, 45% concentrate) fed ad libitum ( TMR) from calving to 75 DPP. At 57 DPP, cows were synchronized for oestrus (day 0, 68 DPP) and at day 7, endometrial biopsies were obtained. The nutritional treatment did not affect insulin, IGF-1 and leptin concentrations on days 0, 4 or 7. Expression of IGF1, IGFBP3, IGFBP4, ADIPOR1 and ADIPOR2 mRNA was significantly affected by the nutritional treatment. Endometrial IGF1 and IGFBP4 mRNA were twofold greater in TMR and HA than MA and LA cows. Expression of IGFBP3 and ADIPOR1 mRNAs was greater in TMR and HA than MA cows, but did not differ from LA cows. All groups had greater expression of ADIPOR2 mRNA than MA cows. This study provided solid evidence of the importance of nutritional management during early lactation on uterine environment at the end of the voluntary waiting period. The greater expression of genes related to embryo growth and uterine function ( IGF system, progesterone and adiponectin receptors) in cows fed diets maximizing energy intake suggests a favourable environment for embryonic growth, which may explain the improved reproductive performance of cows in good energy balance. [ABSTRACT FROM AUTHOR]

Enhancing pasture persistence is crucial to achieve more sustainable grass-based animal production systems. Although it is known that persistence of perennial ryegrass is based on a high turnover of tillers during late spring and summer, little is known about other forage species, particularly in subtropical climates. To address this question, this study evaluated survival of grazed tall fescue tillers growing in a subtropical climate. We hypothesized that hard tactical grazing during winter to remove reproductive stems (designated as 'flowering control'), and nitrogen fertilization in spring, would both improve tiller survival over summer, and thus enhance tiller density. This was assessed in two experiments. In both experiments, few tillers appeared during late spring and summer and so tiller density depended on the dynamics of vegetative tillers present in the sward in spring. In Experiment 2, flowering control and nitrogen fertilization both enhanced the survival of that critical tiller cohort, but the effects were not additive. Responses were similar but not statistically significant in Experiment 1, which had a warmer, drier summer and lower overall survival rates. Unlike grasses in temperate environments, persistence of tall fescue in this subtropical site appeared to follow a 'vegetative pathway'; i.e., new tillers were produced largely in autumn, from vegetative tillers that survived the summer. [ABSTRACT FROM AUTHOR]

The intensification of milk production has required the development of new feeding strategies such as the use of mixed rations either with or without access to grazing. The aim of this study was, to determine milk production and composition, body condition score (BCS), live weight (LW) and grazing behaviour of Holstein dairy cows subject to diets combining mixed rations and herbage during their first 10-wk of lactation (period 1). In addition, both the behavioural adaptation and productive response of cows fed 100% mixed ration when returning to grazing for a 20 days period were examined (period 2). An incomplete randomized block design was used, with 41 early lactation multiparous cows, assigned to treatments: G0 (confined cows fed 100% mixed ration), G1 (6 h access to paddocks+50% mixed ration) and G2 (9 h access to paddock+50% mixed ration). In a second period (11 to 13- wk of lactation), G0 (Post-TMR) cows were managed as G1, with G1 as the control treatment. During the first period, G0 cows produced more milk (37.2 vs 33.7 and 33.9±0.92 L/d; P <0.0001) and more protein (1.25 vs 1.12 and 1.13±0.038 kg/d; P =0.006) than G1 and G2. Nevertheless, no significant differences in fat and lactose production, and output of milk energy were found between G0 and G2 cows. With more access time to the paddock G2 cows could express a higher herbage dry matter intake (DMI) than G1 cows through a higher total grazing time. However, no differences were found on milk production and composition between G1 and G2 cows, probably due to a higher maintenance energy requirement for G2 cows. In period 2 no significant differences were detected in milk production, milk fat and protein production, BCS or LW between Post-TMR and G1 cows. Also, grazing behaviour was not different between G1 and Post-TMR cows, suggesting a prompt adaptation of G0 cows to grazing. It can be concluded that 100% mixed ration systems had higher milk production than grazing plus TMR systems in early lactation. An increase in access time to pastureland allowed higher herbage intake, although with no significant differences in milk energy output. The use of fresh pasture to replace mixed rations after the first 65 DIM allowed maintaining high milk and solids production. [ABSTRACT FROM AUTHOR]

Restricting time for grazing and concentrate supplementation affects feeding motivation, altering grazing behaviour, and performance of grazing ruminants. This study evaluated the combination of three lengths of restricting time at pasture and two levels of concentrate supplementation on behaviour, intake, and productive performance of dairy cows. Times out of pasture were 0, 4 (0800–1200 h) and 8.5 (0800–1630 h) hours. Levels of concentrate supplementation were 3 and 6 kg DM/cow/day. Measurements were: herbage dry matter intake and digestibility, grazing, ruminating and idling time, bite rate, milk yield and composition, as well as changes in live weight and body condition score. Restricting time at pasture increased ( P <0.01) grazing time and length of the initial grazing bout ( P <0.01) and reduced ( P <0.01) rumination and idling times. Restricting time at pasture did not affect herbage intake or milk yield; however, it reduced milk fat concentration ( P <0.01). Supplementation level reduced ( P <0.05) grazing time, but did not affect rumination and idling times. Bite rate was the greatest in cows that were not restricted and had the lowest level in R 8,5 S 6 groups ( P <0.01). Supplementation reduced herbage dry matter intake, and herbage and total organic matter digestibility ( P <0.01). Supplementation increased milk yield ( P <0.05) without effects on milk composition. Modulation of grazing behaviour in response to restricting time at pasture maintained herbage dry matter intake. Changes in grazing behaviour in response to restricting time at pasture plus concentrate supplementation counteract restrictions of restricted time at pasture and thereby help to maintain herbage and energy intake without negative effects on milk production. [ABSTRACT FROM AUTHOR]

In this study we quantify and compare the phenotypic variation in residual feed intake (RFI) in 2 groups of Angus female calves: one carrying simultaneously putative favorable allelic variants (SNP) of neuropeptide Y, leptin, and IGF-1 genes (VAL group) and another devoid of such alleles (CON group). We performed 2 sequential trials: under confinement feeding a high-concentrate diet and under grazing condition. In confinement, 38 purebred Angus female calves [mean age and BW of 247 d (SD = 15) and 186 kg (SD = 33.2), respectively] were offered a total mixed ration diet (60:40 concentrate: alfalfa hay, as fed) ad libitum during 57 d. Dry matter intake was estimated from the difference between offered and refused feed; BW was recorded every 2 wk. Under grazing, 12 heifers from each group were ranked by BW and RFI and randomly assigned to 4 pasture paddocks. Heifers were continuously stocked at high-quality, high-herbage-mass mixed pasture. Herbage DMI was determined using the n-alkane technique. Different models were used to determine RFI: models that use phenotypic data [RFI as described by Koch et al. (1963; RFIK) and RFI as described by ME (RFIME)] and models that use standards feeding data [RFI estimated by Fan et al. (1995; RFIF) and RFI in which the expected DMI was derived from equations in Standing Committee on Agriculture (1990; RFISCA)]. Least squares mean values (SE) of DMI (kg/d), metabolizable energy intake (MEI; Mcal/d), ADG (kg), RFIK (kg DM/d), and feed conversion ratio (FCR; kg DMI/kg ADG) for VAL and CON genotype groups were 6.65 and 6.89 (0.49), 16.7 and 17.4 (1.44), 1.24 and 1.24 (0.03), -0.11 and 0.11 (0.09), and 5.8 and 5.8 (0.14), respectively, in the confinement trial. In the grazing trial least squares mean values (SE) of herbage DMI (kg/d), ADG (kg), MEI (Mcal/d), RFIK, and FCR of VAL and CON groups were 8.76 and 10.93 (0.71), 1.4 and 1.37 (0.05), 25.5 and 31.7 (2.09), -1.02 and 1.02 (0.42), and 6.41 and 6.96 (0.46), respectively. Genotyped groups tended to differ in DMI (P = 0.10), in MEI (P = 0.06), and in RFIK (P = 0.10), differed in RFIF (P = 0.010), and did not differ in ADG or FCR during confinement. During grazing, genotyped groups differed in DMI (P = 0.005), in MEI (P = 0.006), and in RFIK (P = 0.002) but did not differ in ADG and FCR. Our results demonstrate a strong association between these 3 SNP and RFI when animals were grazing on a high-quality, high-availability pasture, whereas a weak effect was observed under confinement. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this study was to assess the effects of restricting access time to pasture and time of grazing allocation on grazing behaviour, daily dry matter intake (DMI), rumen fermentation, milk production and composition in dairy cows. Twenty-one autumn-calving Holstein cows were assigned to one of the following 3 treatments: providing access to a daily strip of pasture for either 8h between 07:00 and 15:00h (T7–15), 4h between 07:00 and 11:00h (T7–11), or 4h between 11:00 and 15:00h (T11–15). The experimental period consisted of 3 weeks of adaptation and 6 weeks of measurements. Cows were offered a daily herbage allowance of 18kg DM/cow to ground level, 6.1kg DM/day of a ground sorghum grain-based supplement and 5.2kg DM/day of maize silage. Milk yield was greater for cows with 8h access time to the pasture (25.4 vs. 24.1 for 8 and 4h access time, respectively). Milk yield was not different between cows that access early (T7–11) or late (T11–15) to the grazing session. Milk protein yield was greater for cows with 8h access time (0.75kg/d) vs. 4h access time treatments (0.72kg/d). Cows with late access time to grazing in the morning produce more protein (0.74kg/d) than cows with early access to the pasture (0.70kg/d). Duration of access had a significant effect on herbage DMI (8.3 vs. 6.6kg/d, for 8 and 4h access, respectively), but there was no significant effect of time of grazing allocation. Intakes of concentrate and maize silage DM did not differ between treatments. Pasture depletion rate was significantly slower when cows had access to the pasture for 8h compared with 4h (0.04 vs. 0.09cm/h), but was not affected by allocation time in the 4-h treatments. Cows grazed for significantly longer in treatment T7–11 than T11–15, achieved significantly more biting and non-biting grazing jaw movements. However, because herbage DMI did not differ between treatments T7–11 and T11–15, it appears that cows grazed more efficiency on treatment T11–15. The present study showed that reducing the period of access to pasture from 8 to 4h decreases DMI and milk production. Cows that started their 4-h grazing session later in the morning (T11–15) produced more protein than cows that started earlier (T7–11), probably as a consequence of a larger bite mass and a tendency for higher intake rate. Rumen pH of cows grazing on treatment T11–15 declined faster than in cows on T7–11, which is in accordance with the higher VFA and ammonia rumen concentrations observed after the grazing session started. [Copyright &y& Elsevier]

Abstract: Neuropeptide Y (NPY), leptin (LEP) and insulin-like growth factor 1 (IGF-1) have been proposed as valuable predictors of relative differences among individuals in the regulation of whole-body energy metabolism. The main objective of this study was to assess the allelic frequency of relevant single nucleotide polymorphisms (SNPs) in NPY, LEP and IGF-1 genes using high resolution melting (HRM) analysis. One hundred thirty six female calves from five Aberdeen Angus stud farms were genotyped. An A/G SNP located in intron 2 of the NPY gene (SNPNPY), a C/T SNP located in exon 2 of the LEP gene (SNPLEP), and a T/C SNP located in the promoter region of IGF-1 gene (SNPIGF-1), were the markers genotyped. The favorable allele frequencies in the whole population were 0.23, 0.48 and 0.39 for SNPNPY, SNPLEP and SNPIGF-1, respectively. The average value of F ST for the three SNPs in the whole population was 0.015. The analysis of these SNPs indicated a low frequency of favorable alleles and a high homogeneity of the Angus population evaluated. The HRM genotyping described in this report provides a convenient alternative approach to identify SNPs in bovine genes. [Copyright &y& Elsevier]

A prolonged postpartum anoestrus (PPA) is related to a low reproductive efficiency in dairy farms, independently of the calving pattern or feeding system. Postpartum luteal activity resumption is coincident with the onset of lactation when the cow is in negative energy balance, which depending on its magnitude could alter the hypothalamus - pituitary - ovary axis of the animal and prolong the PAA. In this article, some results from experiments that manipulated nutrition as a strategy to shorten the PPA, with emphasis in grazing systems, are briefly reviewed. Available information suggests that manipulation of the level and source of dietary energy are promising tools to reduce the length of the PPA in grazing dairy cows and increase the reproductive efficiency in dairy farms. [ABSTRACT FROM AUTHOR]

Abstract: Grass-based diets are of increasing social-economic importance in dairy cattle farming, but their low supply of glucogenic nutrients may limit the production of milk. Current evaluation systems that assess the energy supply and requirements are based on metabolisable energy (ME) or net energy (NE). These systems do not consider the characteristics of the energy delivering nutrients. In contrast, mechanistic models take into account the site of digestion, the type of nutrient absorbed and the type of nutrient required for production of milk constituents, and may therefore give a better prediction of supply and requirement of nutrients. The objective of the present study is to compare the ability of three energy evaluation systems, viz. the Dutch NE system, the agricultural and food research council (AFRC) ME system, and the feed into milk (FIM) ME system, and of a mechanistic model based on Dijkstra et al. [Simulation of digestion in cattle fed sugar cane: prediction of nutrient supply for milk production with locally available supplements. J. Agric. Sci., Cambridge 127, 247–60] and Mills et al. [A mechanistic model of whole-tract digestion and methanogenesis in the lactating dairy cow: model development, evaluation and application. J. Anim. Sci. 79, 1584–97] to predict the feed value of grass-based diets for milk production. The dataset for evaluation consists of 41 treatments of grass-based diets (at least 0.75g ryegrass/g diet on DM basis). For each model, the predicted energy or nutrient supply, based on observed intake, was compared with predicted requirement based on observed performance. Assessment of the error of energy or nutrient supply relative to requirement is made by calculation of mean square prediction error (MSPE) and by concordance correlation coefficient (CCC). All energy evaluation systems predicted energy requirement to be lower (6–11%) than energy supply. The root MSPE (expressed as a proportion of the supply) was lowest for the mechanistic model (0.061), followed by the Dutch NE system (0.082), FIM ME system (0.097) and AFRC ME system (0.118). For the energy evaluation systems, the error due to overall bias of prediction dominated the MSPE, whereas for the mechanistic model, proportionally 0.76 of MSPE was due to random variation. CCC analysis confirmed the higher accuracy and precision of the mechanistic model compared with energy evaluation systems. The error of prediction was positively related to grass protein content for the Dutch NE system, and was also positively related to grass DMI level for all models. In conclusion, current energy evaluation systems overestimate energy supply relative to energy requirement on grass-based diets for dairy cattle. The mechanistic model predicted glucogenic nutrients to limit performance of dairy cattle on grass-based diets, and proved to be more accurate and precise than the energy systems. The mechanistic model could be improved by allowing glucose maintenance and utilization requirements parameters to be variable. [Copyright &y& Elsevier]

This study describes the effect of parity (multiparous versus primiparous) and body condition score (BCS) at calving (<3 or≥3; scale 1–5) on variations of BCS, body weight (BW) and metabolic profiles in Holstein cows grazing on improved pastures. Forty-two cows were studied (21 multiparous and 21 primiparous) from 2 months before to 3 months after calving. BCS, BW and milk production were measured every 2 weeks. Blood samples were taken every 2 weeks to determine total protein, albumin, urea, non-esterified fatty acids (NEFA),β-hydroxybutyrate (BHB), cholesterol, aspartate aminotransferase (AST), calcium, phosphorus and magnesium. Primiparous cows had lower BCS during the early postpartum (PP) period and produced less milk than multiparous. In primiparous cows NEFA concentrations were higher during the early postpartum period; BHB levels were similar in both categories during this period. Primiparous cows showed a more unbalanced metabolic profile than multiparous cows, reflecting that they are recovering from the loss of BCS after calving with less success. [ABSTRACT FROM AUTHOR]

Eighteen Holstein cows (6 ruminally cannulated) were used in the first 60 days of lactation to evaluate the effect of the replacement of corn grain (CG) by crude glycerol (CGly) on organic matter intake (OMI), pasture degradability and milk yield (MY). Cows were blocked [by parity (3.17±1.42), body condition score (3.0±0.3), expected caving date], and assigned randomly to two treatments (T). T1= partially mixed diet (PMR) containing sorghum silage (SS) plus concentrate (CG, wheat grain, soybean expeller, minerals and vitamins) and T2= PMR containing SS plus concentrate where CGly -76.5% glycerol, ALUR Uruguay-replacing the CG. Both groups received PMR in individual feeders and grazed during afternoon in a temperate pasture with herbage allowance-above the ground level-60 kg DM.cow-1.day-1. Chemical composition of PMR (OM, CP, NDF, and EE in g/kgDM) respectively was for T1 [934, 117, 317, and 5] and [927, 106, 297 and 46] for T2. OMI and the ruminal degradation kinetics of DM of pasture were measured in situ in two periods. PMR intake (OMI-PMR) was measured individually as the difference between the amounts offered and refused. OMI-forage was determined with chromium oxide (Cr2O3) and indigestible acid detergent fiber as external and internal marker respectively. In situ data was fitted to nonlinear model D(t)=a+b(1-e-ct), where D= disappearance of DM, (a) soluble fraction, (b) degradable fraction, and (c) degradation rate. MY was Individual measured daily. Intake, degradability parameters, and MY were analyzed with a mixed model whit repeated measures. The model included fixed effects: T, period/week, interaction T*period and cow as a random effect. The statistical analyzes were performed with SAS (2010), data are expressed as lsmeans (s.e) and were considered to differ when P < 0.05. Treatment or interaction did not affect Total organic matter intake, OMI-PMR or OMI-f and was [23.6(1.4), 12.7(0.5) and 10.9 (1.0)] kgOM.d-1 for T1 and [20.8(1.3), 10.9(0.5) and 9.8 (0.9)] kg OM.d-1 for T2 respectively. The parameters "a", "b" "c" of pasture were not affected by T, period or interactions and averaged 20(3.1) g/kgDM 602 (3.6) g/kgDM, 0.04(0.007) h-1. Milk yields was not affected by treatment (30.6(1.0) kg.día-1) or interaction T*week of lactation (WOL) but as expected it was affected for WOL. The absence of negative effects related to the use of CGly in substitution of CG in these conditions allows its use up to 10% DMI for dairy cows without altering the efficiency of the milk production process. [ABSTRACT FROM AUTHOR]

Differences in the grazing harvest process between multiparous (MUL) and primiparous (PRIM) dairy cows could be explained by short-term grazing behavior (i.e., instantaneous herbage intake rate, bite mass, length of the grazing bouts). Therefore, this study was conducted in a randomized block design (3 blocks; n = 9 cows per parity) to assess the effect of parity on herbage intake (HI), HI rate, length of grazing bout, bite rate, and bite mass during the first grazing bout in the am grazing session. Cows (days in milk = 73 ± 7 d; BW = 521 ± 32 kg; BCS = 2.75 ± 0.25; milk yield = 26 ± 3 kg) grazed a vegetative oat pasture (8 h of access to pasture from 8:30 to 16:30 h; pasture allowance = 30 kg DM/d; DM = 14%, CP = 23%, NDF = 46%, DM basis) and were individually fed 6 kg DM/d of a mixture (70:30 forage to concentrate ratio, as-fed basis) after pm milking. Herbage intake was estimated by weighing animals before and after grazing with correction for insensible weight loss (2 consecutive d). The HI rate (kg DM/min) was estimated by dividing HI by the length of the grazing bout, bite rate (bite/min) by counting prehension bites during 1 min every 2 min, and the bite mass (g DM/bite) by dividing HI by the number of bites. Data were analyzed using a mixed model with parity as a fixed effect and block as a random effect. Cow HI (5.6 vs. 4.5 ± 0.35 kg DM/d; P = 0.043 and 0.096 vs. 0.087 ± 0.005 kg DM/kg BW; P = 0.088), HI rate (0.051 vs. 0.043 ± 0.003 kg DM/min; P = 0.008), and bite mass (0.98 vs. 0.79 ± 0.07 g DM; P = 0. 013) were greater for MUL than PRIM while bite rate and the length of the grazing bout did not differ (P > 0.10) between parities. Results indicate that bite mass plays a central role in the short-term intake behavior when MUL and PRIM dairy cows were compared. Differences in bite mass could be explained by grazing adaptability, hierarchical relationships, or physical factors (i.e., mouth dimension). [ABSTRACT FROM AUTHOR]