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.

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.

Existing methods for estimating individual dairy cow energy balance typically either need information on feed intake, that is, the traditional input–output method, or frequent measurements of BW and body condition score (BCS), that is, the body reserve changes method (EBbody). The EBbody method holds the advantage of not requiring measurements of feed intake, which are difficult to obtain in practice. The present study aimed first to investigate whether the EBbody method can be simplified by basing EBbody on BW measurements alone, that is, removing the need for BCS measurements, and second to adapt the EBbody method for real-time use, thus turning it into a true on-farm tool. Data came from 77 cows (primiparous or multiparous, Danish Holstein, Red or Jersey) that took part in an experiment subjecting them to a planned change in concentrate intake during milking. BW was measured automatically during each milking and real-time smoothed using asymmetric double-exponential weighting and corrected for the weight of milk produced, gutfill and the growing conceptus. BCS assessed visually with 2-week intervals was also smoothed. EBbody was calculated from BW changes only, and in conjunction with BCS changes. A comparison of the increase in empty body weight (EBW) estimated from EBbody with EBW measured over the first 240 days in milk (DIM) for the mature cows showed that EBbody was robust to changes in the BCS coefficients, allowing functions for standard body protein change relative to DIM to be developed for breeds and parities. These standard body protein change functions allow EBbody to be estimated from frequent BW measurements alone, that is, in the absence of BCS measurements. Differences in EBbody levels before and after changes in concentrate intake were calculated to test the real-time functionality of the EBbody method. Results showed that significant EBbody increases could be detected 10 days after a 0.2 kg/day increase in concentrate intake. In conclusion, a real-time method for deriving EBbody from frequent BW measures either alone or in conjunction with BCS measures has been developed. This extends the applicability of the EBbody method, because real-time measures can be used for decision support and early intervention.

This is the second of two papers describing a teleonomic model of individual performance during growth and over repeated reproductive cycles throughout the lifespan of dairy cattle. The model described in the first paper is based on the coupling of a regulating sub-model of the dynamic partitioning of a female mammal’s priority over a lifetime with an operating sub-model of whole-animal performance. The model provides a reference pattern of performance under normal husbandry and feed regimen, which is expressed in this paper in a reference dynamic pattern of energy partitioning adapted to changes in nutrient supply. This paper deals with the representation of deviations from the reference pattern of performance. First, a model of intake regulation, accounting for feed allowance, physical limitation of the digestive tract and energy demand, is used to determine the actual intake, which may generate a deviation from the energy input under the reference pattern of partitioning. Second, a theoretical model is proposed to apportion the energy deviation between flows involved in performance and thus simulate lifetime performance when actual intake is above or below requirements. The model explicitly involves a homeorhetic drive by way of the tendency to home on to the teleonomic trajectory and a homeostatic control by way of the tendency to maintain an energy equilibrium in response to nutritional constraints. The model was evaluated through simulations reproducing typical feeding trials in dairy cows. Model simulations shown in graphs concern the effect of dietary energy content on intake, body weight and condition score, and milk yield. Results highlight the ability of the model to simulate the combination of physical and energetic regulation of intake, the accelerated, retarded and compensatory patterns of growth and the short- and long-term residual effects of pre-partum feeding on lactation.

The prediction of the control of nutrient partitioning, particularly energy, is a major issue in modelling dairy cattle performance. The proportions of energy channelled to physiological functions (growth, maintenance, gestation and lactation) change as the animal ages and reproduces, and according to its genotype and nutritional environment. This is the first of two papers describing a teleonomic model of individual performance during growth and over repeated reproductive cycles throughout the lifespan of dairy cattle. The conceptual framework is based on the coupling of a regulating sub-model providing teleonomic drives to govern the work of an operating sub-model scaled with genetic parameters. The regulating sub-model describes the dynamic partitioning of a mammal female’s priority between life functions targeted to growth (G), ageing (A), balance of body reserves (R) and nutrient supply of the unborn (U), newborn (N) and suckling (S) calf. The so-called GARUNS dynamic pattern defines a trajectory of relative priorities, goal directed towards the survival of the individual for the continuation of the specie. The operating sub-model describes changes in body weight (BW) and composition, foetal growth, milk yield and composition and food intake in dairy cows throughout their lifespan, that is, during growth, over successive reproductive cycles and through ageing. This dynamic pattern of performance defines a reference trajectory of a cow under normal husbandry conditions and feed regimen. Genetic parameters are incorporated in the model to scale individual performance and simulate differences within and between breeds. The model was calibrated for dairy cows with literature data. The model was evaluated by comparison with simulations of previously published empirical equations of BW, body condition score, milk yield and composition and feed intake. This evaluation showed that the model adequately simulates these production variables throughout the lifespan, and across a range of dairy cattle genotypes.

We hypothesized that expression of immunity to gastrointestinal nematodes and its relationship with dietary metabolizable protein (MP) supply in ewes depended on body protein- but not on body fat reserves. Twin-bearing ewes were trickle infected with Teladorsagia circumcincta. Three mid-pregnancy feeding treatments were used, calculated to maintain body reserves (HH), maintain body protein- and lose body fat reserves (HL), or lose body reserves (LL), and followed by 2 iso-energetic, periparturient feeding treatments, calculated to provide either scarce (LP) or adequate (HP) amounts of MP. At the end of the mid-pregnancy feeding treatment, HL- and LL-ewes had a smaller backfat depth (∼body fat reserves) than HH-ewes, and LL-ewes had a smaller muscle depth (∼ body protein reserves) and higher faecal egg counts (FEC) than HH- and HL-ewes. Overall, LL-ewes had higher periparturient FEC than HH- and HL-ewes, and LP-ewes had higher periparturient FEC than HP-ewes. However, LL-ewes offered the LP feed had higher periparturient FEC than ewes on any of the other combinations of feeding treatments. Feeding treatments affected plasma pepsinogen but not plasma IgA. The results support the view that body protein- but not body fat reserves may overcome consequences of dietary MP scarcity on periparturient breakdown of immunity to gastrointestinal nematodes.