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Grazing management significantly contributes to low beef production in cow-calf systems within the Rio de la Plata native grasslands. An herbage allowance (HA) of 4 kg DM/kg BW increased the productive response of primiparous cows grazing shallow soils compared to 2.5. However, the impact of HA on metabolic changes and its association with productive response were not studied. We studied two levels of native grassland HA from -150 days relative to calving (DC) to weaning (195 DC) in spring-calving primiparous beef cows undergoing temporary weaning (TW) and flushing at 86 ±â€¯12 DC on herbage intake (HI), body condition score (BCS), BW, milk yield, calf weight, concentrations of metabolic hormones, and the probability of ovulation and pregnancy. Thirty-one heifers were assigned to HA treatments that fluctuated throughout seasons: autumn (-150 to -90 DC) at 5 and 3 kg DM/kg BW, winter (-90 to 0 DC) at 3 and 3 kg DM/kg BW, and spring-summer (0 to 195 DC) at 4 and 2 kg DM/kg BW for High and Low HA, respectively. Data were analysed using linear models and generalised linear models for continuous and categorical variables, respectively. During the autumn period, HI, insulin, IGF-I, BCS, and BW were higher in High HA than Low, despite small differences in herbage mass between HA. Throughout the winter, spring, and summer, HI, insulin, leptin, and BCS changes did not differ between HA. However, IGF-I concentrations were greater at -65 and -40 DC (84 vs 55 ±â€¯8.6 ng/mL; P < 0.05) and tended to be greater after TW in High HA than Low. The probability of ovulation did not reach significance (0.94 vs 0.75 ±â€¯0.11 for High and Low HA, respectively; P = 0.125), while the probability of pregnancy was greater in High HA than in Low HA (0.9 vs 0.61 ±â€¯0.10; P = 0.07). Ovulation probability exhibited a positive association with IGF-I concentrations at -90 and -40 DC (P < 0.05), but not postpartum. Milk yield did not differ between treatments, while calf weight was heavier at weaning in High HA cows (194 vs 178 ±â€¯3.3 kg; P < 0.05). High HA enhances autumn HI and BCS and generates a carry-over effect on IGF-I concentrations throughout winter and after TW ("metabolic memory"), explaining the better reproductive response. Moderate changes in cows' nutrition during autumn contribute to changes in metabolic status and reproductive outcomes in primiparous cows grazing moderate herbage production native grasslands.

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Under climate change, animal breeding faces severe nutritional challenges, exhibiting their resilience and efficiency to survive and produce. The animals' robustness can be evaluated through the use and reconstitution of body reserves (BR). This study investigated the dynamics of ewes' BR, measured through body weight (BW) and the body condition score (BCS), and their effect on production performances of 480 ewes belonging to fat-tailed Barbarine (BB) and thin-tailed Queue Fine de l'Ouest (QFO) ewes over two consecutive years. The BW and BCS were recorded across physiological stages. Reproductive parameters and lambs' growth were calculated. For both years and breeds, the decrease in the BCS between mating and lambing showed BR mobilization to balance nutritional restrictions, which continues until suckling; after weaning, a BR accretion was noted. The lambs' birth weight was similar regardless of the dams' BCS at lambing, though it was lower in the second year (3.5 vs. 4 kg). Lambs' growth parameters depended on ewes' BCS at lambing and weaning. Fertility rates changed with BCS changes and the higher values (80%) were recorded for ewes with BCSs between 2 and 2.5. However, prolificacy was similar for both breeds and years (p > 0.05). In conclusion, ewes have developed adaptative capacities through BR mobilization to cope with environmental challenges and successfully rear their offspring. To maintain a high offspring growth rate, it is recommended to plan correct flock nutrition during suckling.

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Droughts, which can affect feed production, are projected to become more common under future climate conditions. In light of this, breeding cattle resilient to changes in feeding regimens is increasingly becoming an important topic. Body reserves can play a crucial role when feed resources are limited. We simulated populations of dairy cows selected with 2 different breeding goals: one reflecting the current breeding goal and the other placing weight on minimum level of body reserves in early lactation and change in body reserves during lactation. We considered this latter as a breeding goal for resilience. We used the 2 dynamic simulation programs ADAM and AQAL to predict performance of the cows after selection. In AQAL, we modeled moderate and severe drought by decreasing feed quality and quantity offered to cows during one year. We compared cows selected with the 2 breeding goals under 3 environments: without disturbances related to climate and with moderate and severe drought. In the environments without disturbances and the moderate drought, the cows selected with the current breeding goal had higher lifetime lactation efficiency (energy invested in milk/energy acquired from feed) and lower carbon footprint per kilogram of protein in milk and meat than cows selected for resilience. However, with severe drought, cows selected for resilience had higher lifetime lactation efficiency and lower carbon footprint per kilogram of protein in milk and meat than those selected with the current breeding goal. This suggests that cows selected for high productive performance do not perform well under very limiting conditions, leading to increased climate impact. The importance of inclusion of body reserves as a resilience trait in dairy cattle breeding depends on the future environment in which the cows will be used.

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In situations of negative energy balance (NEB) due to feed scarcity or high physiological demands, body energy reserves (BRs), mainly stored in adipose tissues, become the main sources of energy for ruminants. The capacity to mobilise and restore such BRs in response to different challenges is of major concern in the current context of breeding for resilience. Body condition score (BCS) is a common, practical indicator of BR variations throughout successive productive cycles, and quantitative tools for characterising such dynamics at the individual level are still lacking. The main objective of this work was to characterise body condition dynamics in terms of BR mobilisation and accretion capacities of meat sheep during their productive lifespan through a modelling approach, using BCS measurements. The animal model used in this work was the reproductive meat ewe (n = 1 478) reared in extensive rangeland. Regular measurements of BCS for each productive cycle were used as the indicator of BR variations. A hybrid mathematical model and a web interface, called PhenoBR, were developed to characterise ewes' BCS variations through four synthetic and biologically meaningful parameters for each productive cycle i: BR accretion rate (kbi), BR mobilisation rate (kpi), plus the time of onset and the duration of the BR mobilisation, tbi and ΔTi, respectively. The model PhenoBR converged for all the ewes included in the analysis. Estimation of the parameters indicated the inter-individual variability for BR accretion and mobilisation rates, and the length of the mobilisation period. The present study is a proof of concept that the combination of data-driven and concept-driven models is required for the estimation of biologically meaningful parameters that describe body reserve dynamics through consecutive productive cycles. Individual characterisation of animals by these parameters makes it possible to rank them for their efficiency in the use of body reserves when facing NEB challenges. Such parameters could contribute to better management and decision-making by farmers and advisors, e.g. by adapting feeding systems to the individual characteristics of BR dynamics, or by geneticists as criteria to develop future animal breeding programmes including BR dynamics for more robust and resilient animals.

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A wide range of nutritional and non-nutritional factors influence milk fat synthesis and explain the large variation observed in dairy herds. The capacity of the animal to synthesize milk fat will largely depend on the availability of substrates for lipid synthesis, some of which originate directly from the diet, ruminal fermentation or from adipose tissue stores. The mobilization of non-esterified fatty acids from adipose tissues is important to support the energy demands of milk synthesis and will therefore have an impact on the composition of milk lipids, especially during the early lactation period. Such mobilization is tightly controlled by insulin and catecholamines, and in turn, can be affected indirectly by factors that influence these signals, namely diet composition, lactation stage, genetics, endotoxemia, and inflammation. Environmental factors, such as heat stress, also impact adipose tissue mobilization and milk fat synthesis, mainly through endotoxemia and an immune response-related increase in concentrations of plasma insulin. Indeed, as proposed in the present review, the central role of insulin in the control of lipolysis is key to improving our understanding of how nutritional and non-nutritional factors impact milk fat synthesis. This is particularly the case during early lactation, as well as in situations where mammary lipid synthesis is more dependent on adipose-derived fatty acids.

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This study aimed to evaluate the impact of body condition score (BCS) at calving, parity, and the calving season on the performance of dairy cows and their offspring. Data from 521 Holstein cows that calved a female calf and had their BCS evaluated at calving from a single commercial farm located in Southern Brazil were used. Cows were categorized into five BCS classes: class 1: <3.0 (n = 19), class 2: 3.0-3.25 (n = 134), class 3: 3.5-3.75 (n = 160), class 4: 4.0-4.25 (n = 142), and class 5: >4.25 (n = 66). Data were also categorized by calving order (primiparous and multiparous dams) and by calving season. The study was designed as a prospective cohort study. Variables with normal distribution were analyzed by the MIXED procedure of SAS, while binary outcomes were analyzed by the GLIMMIX procedure of SAS. Daughters from primiparous dams were born lighter (39.1 ± 0.42 vs. 41.4 ± 0.29 kg, p < 0.01), but they had the same weights as the daughters from multiparous cows at weaning (121.5 ± 1.67 vs. 120.4 ± 1.58 kg, p = 0.20). As expected, primiparous cows showed lower (p < 0.01) 305-day milk yields than multiparous ones: 8633 ± 363 vs. 10,761 ± 249 kg, respectively. Regarding the calving season, cows that calved in the winter were the most productive ones, and those that calved in the fall had lower milk yields (p = 0.01). Calves born in the winter were heavier at birth (p < 0.01), calved younger (p = 0.04), and produced more milk at first lactation (p = 0.03). The BCS class had an impact (p < 0.01) on calf birth weights; daughters from Class 1 cows (BCS < 3.0) were lighter (38.0 ± 1.0 kg) than the calves from Class 5 cows with a BCS > 4.25 (41.9 ± 0.57 kg). Calves from dams with a BCS < 3 (Class 1) had a 31.8% culling rate until weaning, while calves from cows with a BCS of 3.0-3.25 (Class 2) had a 9.6% culling rate (p = 0.12). These results suggest that maternal and environmental factors, such as calving season and parity, in addition to the dams' body condition score at calving, are associated with different offspring performances.

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The microbiota influences hosts' health and fitness. However, the extent to which the microbiota affects host' foraging decisions and related life history traits remains to be fully understood. Our study explored the effects of microbiota manipulation on foraging preference and phenotypic traits of larval and adult stages of the polyphagous fruit fly Bactrocera tryoni, one of the main horticultural pests in Australia. We generated three treatments: control (non-treated microbiota), axenic (removed microbiota), and reinoculation (individuals which had their microbiota removed then re-introduced). Our results confirmed that axenic larvae and immature (i.e., newly emerged 0 day-old, sexually-immature) adults were lighter than control and reinoculated individuals. Interestingly, we found a sex-specific effect of the microbiota manipulation on carbohydrate intake and body composition of 10 day-old mature adults. Axenic males ate less carbohydrate, and had lower body weight and total body fat relative to control and reinoculated males. Conversely, axenic females ate more carbohydrate than control and reinoculated ones, although body weight and lipid reserves were similar across treatments. Axenic females produced fewer eggs than control and reinoculated females. Our findings corroborate the far-reaching effects of microbiota in insects found in previous studies and show, for the first time, a sex-specific effect of microbiota on feeding behaviour in flies. Our results underscore the dynamic relationship between the microbiota and the host with the reinoculation of microbes restoring some traits that were affected in axenic individuals.

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Evolution of milk production, body reserves and blood metabolites and their relationships with dietary carbohydrates were compared in 30 Sarda dairy ewes and 26 Saanen dairy goats in mid-lactation. From 92 to 152 ± 11 days in milk (DIM), each species was allocated to two dietary treatments: high-starch (HS: 20.0% starch, on DM basis) and low-starch (LS: 7.8% starch, on DM basis) diets. In mid-lactating goats, the HS diet increased fat-corrected milk yield (FCM (3.5%); 2.65 vs. 2.53 kg/d; p = 0.019) and daily milk net energy (NEL; p = 0.025), compared to the LS diet. The body condition score (BCS) was not affected. In mid-lactating ewes, the LS diet increased FCM (6.5%) (1.47 vs. 1.36 kg/d; p = 0.008), and NEL (p = 0.008), compared to the HS diet. In addition, BCS was greater in HS than in LS ewes (3.53 vs. 3.38; p = 0.008). Goats had a higher growth hormone (GH) and lower insulin concentration than ewes (GH: 2.62 vs. 1.37 ng/mL; p = 0.04; insulin: 0.14 vs. 0.38 µg/L; p < 0.001 in goats and ewes, respectively). In conclusion, in mid-lactation, the two species responded differently to dietary carbohydrates, probably due to differences in the concentration of GH and insulin. The HS diet favored milk yield in goats and body reserve accumulation in ewes. In ewes, the partial replacement of starch with highly digestible fiber increased energy partitioning in favor of milk production.

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Feed efficiency (FE) is a complex phenotype made up of multiple traits for which there is potential for substantial genotype by environment interaction (G × E). The objective of this study is to evaluate the extent of G × E for FE traits with a simulation approach. We used a mechanistic model of the dairy cow that simulates trajectories of phenotypes throughout lifetime, depending on trajectories of resource acquisition and allocation, driven by 4 genetic scaling parameters, and depending on the nutritional environment (quantity and quality of feed resources). The cow model, calibrated for a grass-based farming system and seasonal calving, was combined with a genetic module. This simulated genetic variation in the 4 genetic scaling parameters related to resource acquisition and allocation, based on a simple balanced pedigree structure (200 paternal half-sib groups each of 100 daughters). The population of 20,000 cows generated was simulated in 4 nutritional environment scenarios, representing a gradient of feeding constraints. In each scenario, 6 traits derived from the model outputs were analyzed to obtain population genetic parameters. Genetic correlations between second-lactation production and FE were positive and high in all scenarios and increased as the nutritional environment became more constraining. A measure of lifetime FE was positively correlated with second-lactation production under a less constrained environment, but these correlations decreased as the environment became more constraining. The genetic correlation between body reserves at second calving, and lifetime FE was positive and low in the least constraining scenario and increased as the environment became more constraining. In addition to genetic parameters, we looked at the distributions of acquisition and allocation parameters among the best performing cows for lactation and life FE, in the 2 most contrasted scenarios. The 4 subpopulations of best cows had acquisition and allocation strategies different from the whole population. In conclusion, this simulation study identifies the potential underlying biological basis for important G × E in FE traits. This highlights the importance of having a balanced breeding goal when undertaking selection that should also be based on phenotypes relevant to the target performance environment.

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Breeding for resilience requires a better understanding of intra-flock variability and the related mechanisms responsible for robustness traits. Among such traits, the animals' ability to cope with feed fluctuations by mobilizing or restoring body reserves (BR) is a key mechanism in ruminants. The objective of this work was to characterize individual variability in BR dynamics in productive Romane ewes reared in extensive conditions. The BR dynamics profiles were characterized by combining individual longitudinal measurements of BW and body condition scores (BCS) over several production cycles. Historical data, including up to 2628 records per trait distributed in 1146 ewes, underwent cluster analysis. Two to four trajectories were observed for BW depending on the cycle, while three trajectories were found for BCS, whatever the cycle. Most trajectories suggested that BR dynamics were similar but the level of BR may differ between ewes. Nevertheless, some trajectories suggested that both BR dynamics and levels were different for a proportion of ewes. Clustering on BW and BCS profiles adjusted for individual level trends, resulted in differences only in the level of BW or BCS, rather than differences in trajectories. Thus, the overall shape of trajectories was not changed considering or not the individual level trend across cycles. In addition to individual variability, the ewe's age at first lambing and litter size contributed to the distribution of the ewes between the trajectories. Regarding the entire productive life, three trajectories were observed for BW and BCS changes over three productive cycles. Increase in BW at each cycle suggested that ewes kept growing up until 3 to 4 years old in our conditions. Similar alternation of BCS gains and losses across cycles suggested BR dynamics might be repeatable. Many individual trajectories remained the same throughout a ewe's life, whatever the age at first lambing, parity or litter size. Our results demonstrate the relevance of using BW and BCS changes for characterizing the diversity of BR mobilization-accretion profiles in sheep in a long timespan perspective.

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A divergent selection experiment on litter size variability (high and low lines) was performed in rabbits over seven generations. The aim of this study was to evaluate the correlated responses to selection in body condition and fat reserves mobilisation. Litter size variability was estimated as phenotypic variance of litter size within female after correcting for the year-season and the parity-lactation status effects. A total of 226 females were used in this study, of which 158 females were used to measure body condition and energy mobilisation. Body condition was measured as BW and perirenal fat thickness. Females were stimulated with the adrenergic isoproterenol. Mobilisation capacity of fat reserves was measured by the lipolytic potential, defined as the increment in non-esterified fatty acids (NEFA) levels from basal concentration until adrenergic stimulation at mating, delivery and 10 days after delivery of the second reproductive cycle. Females were classified as survivor or non-survivor when they were culled for sanitary reasons or died before the third kindling. Data were analysed using Bayesian methodology. Survivor females presented higher BW than the non-survivor females at delivery (238 g, P=1.00) and 10 days after delivery (276 g, P=1.00). They also showed higher perirenal fat thickness at 10 days after delivery (0.62 mm, P=1.00). At delivery, basal NEFA levels was lower in survivor than non-survivor females (-0.18 mmol/l, P=1.00), but their lipolytic potential (∆NEFA) was higher (0.08 mmol/l, P=0.94). Body weight was similar between lines in survivor females. Perirenal fat thickness was lower in the high line than in the low line at delivery (-0.23 mm, P=0.90) and 10 days after delivery (-0.28 mm, P=0.92). The high line exhibited higher NEFA (0.10 mmol/l, P=0.93) and lower ∆NEFA (-0.08 mmol/l, P=0.92) than the low line at delivery. The low line showed a favourable correlated response to selection on body condition and fat reserves mobilisation. In conclusion, the low line selected for litter size variability seems to adapt better to adverse conditions, as it has a greater capacity to mobilise energy reserves at delivery than the high line. Females that adequately manage their body reserves and perform energy mobilisation correctly have a lower risk of dying or being culled.

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Feeding dairy cows indoors or on pasture affects not only labour, machinery and housing costs, but also animals' performance and metabolism. This study investigates the effects of indoor feeding (IF) with a partial-mixed ration (PMR) versus pasture-based feeding (PF) on milk production, fertility, backfat thickness (BFT), body weight (BW) loss and energy metabolism of Brown Swiss (BS) dairy cows with similar genetic production potential. The IF herd consisted of 13 cows fed a PMR composed of maize and grass silage plus protein concentrate according to each cow's requirements. The PF herd consisted of 14 cows offered barn-ventilated hay ad libitum after calving from January until March and grazed on semi-continuous pastures during the vegetation period. The IF cows produced more energy-corrected milk (ECM) per standard lactation (9,407 vs. 5,960 kg; p < .01), more milk fat (378 vs. 227 kg; p < .01) and milk protein (326 vs. 215 kg; p < .01). The calving interval (377 vs. 405 days; p < .01) and time empty (86 vs. 118 days; p < .01) were shorter in the PF compared to IF, possibly also due to different selection criteria for maintaining the respective seasonal calving rhythm. The empty body fat loss calculated according to BCS until its nadir was higher in IF cows (IF: 10.4 vs. PF: 4.8 MJ/day; p < .01), but no differences were noted in total body fat loss estimated via BFT (p = .24). However, PF had lower blood glucose concentration at all investigated time points, but no differences occurred in serum non-esterified fatty acid and ß-hydroxybutyrate concentrations post-partum. In conclusion, BS cows were equally well suited for the IF with PMR and the PF system investigated here without developing a prominent metabolic load despite differences in nutrient supply. As such, investigated BS dairy cows in our trial seem to have a high capacity for metabolic adaptation to different production systems.

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Factors such as temperature, habitat, larval density, food availability and food quality substantially affect organismal development. In addition, risk of predation has a complex impact on the behavioural and morphological life history responses of prey. Responses to predation risk seem to be mediated by physiological stress, which is an adaptation for maintaining homeostasis and improving survivorship during life-threatening situations. We tested whether predator exposure during the larval phase of development has any influence on body elemental composition, energy reserves, body size, climbing speed and survival ability of adult Drosophila melanogaster. Fruit fly larvae were exposed to predation by jumping spiders (Phidippus apacheanus), and the percentage of carbon (C) and nitrogen (N) content, extracted lipids, escape response and survival were measured from predator-exposed and control adult flies. The results revealed predation as an important determinant of adult phenotype formation and survival ability. D. melanogaster reared together with spiders had a higher concentration of body N (but equal body C), a lower body mass and lipid reserves, a higher climbing speed and improved adult survival ability. The results suggest that the potential of predators to affect the development and the adult phenotype of D. melanogaster is high enough to use predators as a more natural stimulus in laboratory experiments when testing, for example, fruit fly memory and learning ability, or when comparing natural populations living under different predation pressures.

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Phenotypic plasticity and phenotypic stability are major components of the adaptive evolution of organisms to environmental variation. The invariant two-egg clutch size of Eudyptes penguins has recently been proposed to be a unique example of a maladaptive phenotypic stability, while their egg mass is a plastic trait. We tested whether this phenotypic plasticity during reproduction might result from constraints imposed by migration (migratory carry-over effect) and breeding (due to the depletion of female body reserves). For the first time, we examined whether these constraints differ between eggs within clutches and between egg components (yolk and albumen). The interval between colony return and clutch initiation positively influenced the yolk mass, the albumen mass, and the subsequent total egg mass of first-laid eggs. This time interval had only a slight negative influence on the yolk mass of second-laid eggs and no influence on their albumen and subsequent total masses. For both eggs, female body mass at laying positively influenced albumen and total egg masses. Female investment into the entire clutch was not related to the time in the colony before laying but increased with female body mass. These novel results suggest that the unique intraclutch egg size dimorphism exhibited in Eudyptes penguins, with first-laid eggs being consistently smaller than second-laid eggs, might be due to a combination of constraints: a migratory carry-over effect on the first-laid egg and a body reserve depletion effect on the second-laid egg. Both these constraints might explain why the timing of reproduction, especially egg formation, is narrow in migratory capital breeders.

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During pregnancy, the maternal body undergoes significant physiological changes. The present study assessed the changes on calcium (Ca), phosphorus (P), magnesium (Mg), sodium (Na) and potassium (K) metabolism in singleton and twin-pregnant dairy goats. The 42 goats used (49.5 kg±7.6 body weight [BW]) were assigned at random to treatments that were factorially arranged to account for 2 breeds (Oberhasli and Saanen), 2 pregnancy types (singleton and twin) and 3 gestation periods (80, 110, and 140 days). Digestibility trials were performed at 80, 110, and 140 days of gestation. Mineral retention during pregnancy was determined in the maternal body, femur, uterus, mammary gland, fetus and fetal fluid. Blood samples were taken during pregnancy before and after a meal, and Ca, P, Mg, Na, K ions and alkaline phosphatase activity determined in serum. Bone mineral density was determined in the right femur. Statistical analyses were performed using the SAS MIXED procedure. Dry matter intake decreased linearly up to 140 days of gestation. Maternal BW gain, and Ca, P, and Mg retention (g/kg) decreased linearly with the advance of gestation days. Macromineral retention in maternal body (g/kg) was greater in Oberhasli than Saanen goats, and their fetuses had higher Ca, P, and Mg deposition (mg/g). Mineral retention (mg/g) increased in fetuses according to pregnancy development, with no differences between singleton and twin pregnancy. In the mammary gland, the retention of all minerals (g) increased with the days of pregnancy. In conclusion, related to Ca, P, and Mg metabolism can be divided into two stages. Up to 80 days of gestation, was characterized by the preparation of the maternal body reserves for future mineral demands. From 80 days of gestation onward, was characterized by the transfer of maternal body reserves for fetal development and colostrum production. Na and K supply was provided by adjustments in endogenous excretion and an increase in intestinal absorption. Finally, mineral metabolism was specific to each genotype and, except for Na, was not affected by the number of fetuses.

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Although most of the genetic progress in production efficiency is achieved through selection at a global scale, locally, farm managers can also influence the selection process to better match genotypes and their varying herd environment. This study focused on the influence of a particular management decision--the use of extended lactation (EL) in dairy goat production systems--as it affects the survival and reproduction rates at the herd level, which may then shape different long-term selection responses. The objective was to understand and quantify the influences of EL and variability in achieved intake level on the responses to selection for production, reproduction, and longevity. An animal model of resource allocation between life functions was applied to the dairy goat. It predicts the trajectory of change in the herd genetic composition as affected by the feeding level and the selection pressure applied by the manager. During 40 yr, goats were selected for milk yield, reproduction, and, with a different selection weight for age (WAGE), for longevity. Under varying achieved intake levels, increasing WAGE improved the survival rate but a nonlinear effect was observed for the average milk yield and BCS. When moderately increasing WAGE from 0, resources were reallocated from lactation towards body reserves and survival, which led to a trade-off at the herd level between improving survival and BCS and increasing milk yield. When further increasing WAGE, old females became systematically preferred regardless of their reproductive status and the proportion of EL in the herd increased. Females undergoing EL had reduced energetic costs of reproduction, which improved their probability of survival. Across generations, an increased herd incidence of EL led to a relaxation of the selection pressure on the resource allocation to body reserves, which is normally imposed by the manager's priority to achieve successful reproduction at each mating. As selection for longevity progressed, the incidence of high-producing females increased within the herd, driving a long-term trend in increased milk production. Thus, the use of EL as a management tool led to an alleviation of the trade-off between milk yield progress and survival improvement. Although the model simplifies the underlying physiology of nutrient allocation, it provides insights into how farm manager strategies can influence the development of genotype × environment interactions and promote herd robustness.

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Throughout an entire year, 41 Romane ewes reared in an extensive rangeland were used to investigate temporal changes in body reserves (BRs) and profiles of related metabolites and metabolic hormones. Ewes were allocated to homogeneous groups according to BW and BCS and were distributed by parity (primiparous [PRIM], n = 21; multiparous [MULT], n = 20) and litter size (LSi; lambing singletons [SING], n = 21 or TWINS, n = 20). The feeding system was based on rotational grazing of rangeland paddocks and progressive supplementation with hay, silage, and barley at late pregnancy during the winter. Individual BW, BCS, plasma NEFA, ß-hydroxybutyrate (ß-OHB), glucose, insulin, leptin, and triiodothyronine (T3) were monitored at -56, -12, 8, 49, 76, 107, 156, 195, 216, 246, and 301 d relative to lambing. The BR mobilization was observed from late pregnancy to the end of suckling and varied as a function of the ewe energy balance but also because of transitions from fertilized to native rangeland paddocks and by supplementation. Contrarily, BR accretion occurred from weaning, during the dry-off, and until the start of the next pregnancy. Lipolysis was well reflected by NEFA, ß-OHB, and T3 kinetics. Mean BW (but not mean BCS) was affected by parity (MULT > PRIM), whereas both BW and BCS were influenced by LSi (SING > TWINS) but only for MULT. The most drastic BW loss was observed during the mid-suckling period (49 d in milk [DIM]) in all ewes. The lack of effects of LSi in PRIM but not in MULT was also evident in the majority of blood plasma kinetics, which were affected (P < 0.0001) by physiological stage in all ewes. A tendency to ketosis (ß-OHB) was found in ewes nursing TWINS around lambing, irrespective of parity. Glucose concentrations were greater during suckling and dry-off, and a peak (0.96 ± 0.05 g/L) was attained at 156 DIM in MULT nursing TWINS. The highest plasma leptin concentration was observed during the start and the middle of the next pregnancy in MULT (107-216 DIM; 9.6 ± 0.44 ng/mL). In all ewes the physiological stage affected T3, which was affected by LSi just in MULT (from late pregnancy, MULT by SING > MULT by TWINS; 99.91 vs 85.52 ng/dL) and during suckling (111.7 ± 4.18 ng/dL). Lamb BW was affected at birth and weaning by parity (MULT > PRIM) and LSi (SING > TWINS). Overall, temporal changes in BR were directly affected by the transition of physiological states and feeding levels, whereas individual responses were predetermined by parity. In MULT, the reactivity and magnitude of response was influenced by LSi. The whole set of parameters allowed us to detect sensitive and critical periods throughout the entire annual cycle. We thus identified opportunities for improved nutritional management, for example, during physiological states usually underestimated such as early and mid-pregnancy. This work indicates the applicability of long-term studies about BR dynamics in ruminants as a potential component contributing to farm economic resilience.

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The objective was to evaluate the effect of body condition score (BCS) at 30 days before calving (-30 days) induced by a differential nutritional management, parity and week of lactation (WOL) on milk yield and composition, and milk casein and fatty acid composition. Primiparous and multiparous Holstein cows with high BCS (PH, n = 13; MH, n = 9) and low BCS (PL, n = 9; ML = 8) under grazing conditions were sampled at WOL 2 and 8 (before and after peak of lactation). Milk yield was greater in multiparous than in primiparous cows and tended to decrease from WOL 2 to 8 only in ML cows. Milk protein, fat and casein yields were greater in multiparous than in primiparous cows and decreased from WOL 2 to 8. Milk casein concentration in milk protein was greater in MH cows than in ML, PH and PL cows at WOL 2. Milk κ-casein was greater, and ß-casein was less in multiparous than in primiparous cows. As lactation progressed, proportion of casein fractions were not altered. Only κ-casein fraction was affected by BCS at -30 days as PL showed a higher concentration than PH. The de novo (4:0-15:1) and mixed-origin fatty acids (16:0-16:1) in milk fat increased, whereas preformed fatty acids (≥17:0) decreased from WOL 2 to 8. Saturated (SAT) fatty acids tended to be greater and monounsaturated fatty acids (MUFA) were less in multiparous than in primiparous cows. High-BCS cows had greater concentrations of polyunsaturated (PUFA), conjugated linoleic acid (CLA) as well as n-6 and n-3 fatty acids in milk fat than low-BCS cows. The results indicate that casein and fatty acid fractions in milk were affected by parity and may be modified by a differential nutritional management during the pre-calving period (BCS at -30 days) in cows under grazing conditions.

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Several aspects of the life history of reindeer (Rangifer tarandus) are related to the nutritional condition of the animals. Moreover, compensatory growth and fattening in summer decreases with age. The interaction of tooth wear and the standing crop of lichens on age-related variation in body size and tissue reserves was examined to evaluate the proximate causes of density-dependent food limitation on life history parameters in female reindeer. Studies in nine semi-domesticated free-ranging reindeer herds showed that molar height depended on the mean standing crop of terrestrial lichens in winter habitats. The extent of tooth wear had the strongest effect on body reserves among the oldest females (11-14 years). This indicates that severe tooth wear limits the animals´ ability to process food efficiently and, hence, to maintain their body reserves. Both tooth wear and the biomass of lichens influenced body mass in old females, probably because on heavily exploited winter ranges reindeer had to use higher proportions of lower-ranking coarser foods, especially dwarf shrubs.