Search

As a sustainable food production may increasingly build on resilient, low-input farming systems, enhancing livestock reliance on natural processes is of growing interest. In this respect, small ruminants present various assets sincethey cover a broad diversity of breeds adapted to contrasting environments, including harsh and variable rangeland conditions where they evolved strong adaptive capacities. Yet, from an agroecological perspective, adaptive capacitiesremain poorly accounted for into current management and breeding strategies. Several traits reflecting aspects of resilience to undernutrition or to infections are amenable to selection and can thereby contribute to reduce the inputsneeded for production or to an integrated health management. However, the consideration of adaptive capacities in breeding schemes generally targets conventional production systems and has only little scope for their re-design.Then, a more rigorous assessment of adaptive capacities would require to examine trade-offs among resilience traits, between resilience traits and production traits, during lifetime and across environments – which is virtually outof reach using classic experimental means. Finally, few studies have started to explore how improving individual adaptive capacities or managing their diversity within the herd can affect farm resilience, even though this aspect iskey in agroecology. Given previous limitations, the use of systemic approaches integrating the mechanistic basis of adaptive capacities as well as their consequences on herd performances holds promise. Specifically, we illustrate atthe animal level how resource allocation models could contribute to an integrative assessment of adaptive capacities, including their genetic trade-offs with production traits. In turn, the use of such individual models in herd simulationshould allow identifying synergies between breeding and management strategies to promote herd resilience. Beyond, expanding this modelling at the farming system level may support the design of new agroecosystems, particularlythose enhancing crop-livestock integration.

International audience; Trade-offs between life history traits are expected to occur due to the limited amount of resources that organisms can obtain and share among biological functions, but are of least concern for selection responses in nutrient-rich or benign environments. In domestic animals, selection limits have not yet been reached despite strong selection for higher meat, milk or egg yields. Yet, negative genetic correlations between productivity traits and health or fertility traits have often been reported, supporting the view that trade-offs do occur in the context of nonlimiting resources. The importance of allocation mechanisms in limiting genetic changes can thus be questioned when animals are mostly constrained by their time to acquire and process energy rather than by feed availability. Selection for high productivity traits early in life should promote a fast metabolism with less energy allocated to self-maintenance (contributing to soma preservation and repair). Consequently, the capacity to breed shortly after an intensive period of production or to remain healthy should be compromised. We assessed those predictions in mammalian and avian livestock and related laboratory model species. First, we surveyed studies that compared energy allocation to maintenance between breeds or lines of contrasting productivity but found little support for the occurrence of an energy allocation trade-off. Second, selection experiments for lower feed intake per unit of product (i.e. higher feed efficiency) generally resulted in reduced allocation to maintenance, but this did not entail fitness costs in terms of survival or future reproduction. These findings indicate that the consequences of a particular selection in domestic animals are much more difficult to predict than one could anticipate from the energy allocation framework alone. Future developments to predict the contribution of time constraints and trade-offs to selection limits will be insightful to breed livestock in increasingly challenging environments.

Les filières et systèmes d’élevage ont considérablement évolué au cours du XXe siècle. La recherche en génétique animale et la mise en place des programmes d’amélioration génétique ont joué un rôle important dans cette évolution. Aujourd’hui, le modèle dominant, caractérisé par une utilisation intensive d’intrants, une très grande spécialisation des systèmes et la recherche de coûts de production toujours plus bas, est remis en cause. Un objectif désormais largement partagé est de contribuer à l’émergence de systèmes alimentaires durables, équitables, sains et respectueux de l’environnement. L’agroécologie est un moyen pour atteindre cet objectif et guider la nécessaire transition des systèmes d’élevage, à laquelle la génétique animale doit contribuer. Des exemples de contributions passées, actuelles et potentielles sont présentés et positionnés selon cinq principes d’agroécologie proposés pour guider l’évolution des systèmes d’élevage. La plupart, telles que la sélection d’animaux résistants à différentes maladies infectieuses ou valorisant de façon plus efficace leur alimentation, correspondent à des niveaux de transition agroécologique faible, dans la mesure où elles ne remettent pas en cause les fondements, les composantes ou la conception générale des systèmes. De nouvelles contributions, visant une transition forte, fondée sur une reconception en profondeur des systèmes d’élevage, sont à développer à l’avenir.

Individual body mass often positively correlates with survival and reproductive success, whereas fitness costs of growing large are rarely detected in vertebrates in the wild. Evidence that adult body mass progressively declines with increasing age is accumulating across mammalian populations. Growing fast to a large body can increase the cellular damage accumulated throughout life, leading body growth in early life to be negatively associated with the rate of body mass senescence. Moreover, the onset of mass senescence may strongly depend on both sex-specific reproductive tactics and environmental conditions. Assessing the timing and the rate of body mass decline with increasing age thus offers an opportunity to look for costs of having grown fast, especially after a poor start during early life, in both sexes and in different environments. Using a unique dataset including 30 years of longitudinal data on age-specific body mass collected in two roe deer Capreolus capreolus populations subjected to contrasted environmental conditions, we looked for potential costs of high post-weaning growth rate in terms of steeper rate of body mass senescence. Our analyses of body mass senescence accounted for the potential variation in the onset of senescence and allowed explicit comparisons of this variable between sexes and populations. Higher growth rates late in the growing period (after weaning) were associated with a steeper rate of body mass senescence, regardless of early mass (gained before weaning), but at different extents depending on sex and environmental conditions. Body mass senescence occurred earlier in males than in females, especially in the population facing limiting resources. In the wild, although heavy individuals generally survive better than small ones, the costs of growing large late in the growing period only became apparent late in life through mass senescence. This article is protected by copyright. All rights reserved.

The main effect of climate change on livestock production systems in the Mediterranean area is to induce changes in feed resource availability. In face of constraining and changing environmental conditions, the challenge is to find practical solutions for herd management to minimize farmer's risk. These solutions should be good enough in terms of efficiency (E), to ensure sufficient income, and good enough in terms of resilience (R), to ensure farm sustainability. The objective of the ADAPT-HERD project is to develop simulation tools capable of evaluating the consequences of management strategies at the herd level, under contrasting and varying environments (Egypt, France, Spain and Tunisia). Our approach considers that biological adaptive capacities of small ruminants can be fully integrated within management strategies to improve R and E by: i) using reproduction practices that provide the best match between herd demand and feed supply; ii) managing groups of animals based on their adaptive capacities (targeting interventions) and iii) managing herd demography to adapt animal numbers to future feed resources. The project will implement data acquisition at animal level (fine-grained experiments on adaptive capacities and phenotyping of local breeds) and at production system level (herd management, feed resource, climate and market conditions). Data will be combined and used in computer simulations to explore different climate change scenarios and management strategies and evaluate their effects on herd R and E. Interfacing modelling tools will be a key aspect of the project, fostering knowledge exchange and collaboration, especially with ongoing projects focusing on genetic selection and breeding solutions to improve R&E in small ruminants.

International audience; According to the principle of allocation, trade-offs are inevitable when resources allocated to one biological function are no longer available for other functions. Growth, and to a lesser extent, immunity are energetically costly functions that may compete with allocation to reproductive success and survival. However, whether high allocation to growth impairs immune system development during the growing period or immune system performance during adulthood is currently unknown in wild mammals. Using three roe deer (Capreolus capreolus) populations experiencing contrasting environmental conditions, we tested for potential costs of growth on immune phenotype over both the short-term (during growth), and the long-term (during adulthood) over the course of an individuals' life. We investigated potential costs on a set of 12 immune traits that reflect both innate and adaptive responses, and compared them between sexes and populations. Although fast growth tended to be associated with low levels of some humoral traits (globulins) during the growing period and some cellular immune traits (i.e. eosinophil and neutrophil counts) during adulthood, evidence for a trade-off between growth and other immune components was limited. Unexpectedly, no detectable growth costs on immunity were found in females from the population experiencing the least favourable environment. We discuss our findings in the light of the complex interplay between resource allocation strategies among reproduction, maintenance and immunity, in relation to local environmental conditions experienced by roe deer.

International audience; To secure mating opportunities, males often develop and maintain conspicuous traits that are involved in intrasexual and/or intersexual competition. While current models of sexual selection rely on the assumption that producing such traits is costly, quantifying the cost of allocating to secondary sexual traits remains challenging. According to the principle of allocation, high energy allocation to growth or sexual traits in males should lead to reduced energy allocation to the maintenance of cellular and physiological functions, potentially causing them to age faster, with impaired survival. We evaluated the short-term and delayed consequences of energy allocation to antlers early in life in two contrasted populations of roe deer, Capreolus capreolus. Although most males mate successfully for the first time in their fourth year, antlers are grown annually from the first year of life onwards. We tested the prediction that a high level of allocation to antler growth during the first two years of life should lead to lower body mass, antler size and survival during the early and late prime stages, as well as to reduced longevity overall. Growing and carrying long antlers during the first years of life was not associated with any detectable cost in the late prime stage. The positive association between antler growth in early life and adult body mass instead supports that fawn antler acts as an honest signal of phenotypic quality in roe deer. For a given body mass, yearling males growing longer antlers displayed impaired performance during their late prime. We also found a trend for a short-term survival cost of allocation to relative antler length during the second year of life. Yearling males that grow long antlers relative to their mass might display a fast life-history tactic. We argue that differential allocation to secondary sexual traits generates a diversity of individual trajectories that should impact population dynamics.

Selection for high levels of prolificacy has allowed substantial improvements in the production efficiency of New Zealand (NZ) sheep farms, but the consequences on ewe lifetime performance are mostly unknown. In this study, the relationship between the level of prolificacy early in ewes' productive lives and their probability to survive later (i.e. stayability) was evaluated in two contrasting NZ flock environments. Records were obtained from 6605 ewes from four ram breeder flocks representing either a moderate (n = 2) or a highly variable (n = 2) nutritional environment. All ewes lambed for the first time at 2 years of age and were mated the following year. The number of lambs born during the first 2 years of productive life (NLB2-3) was used as a measure of early prolificacy. Effects of NLB2-3 on stayability to 4, 5, 6, 7 and 8 years old were analysed using logistic regression. Curvilinear effects (logit-transformed) were detected (P < 0.05) until stayability to 6 years and to 8 years old in the highly variable and the moderate environment, respectively. The NLB2-3 that resulted in maximum expected stayability to various ages was 3.9 to 4.2, and 4.5 to 4.7 lambs in the highly variable and in the moderate flock environments, respectively. In addition, ewe stayability was reduced when the proportion of the litter that survived from birth to weaning (i.e. ewe rearing ability) was submaximal during the early productive life. High prolific ewes had a low rearing ability whatever the environment whereas the rearing ability of lowly prolific ewes was apparently more sensitive to the nutritional environment. The poor maternal performance of ewes with low levels of NLB2-3 led to a premature culling by breeders whereas the high early reproductive effort associated with high levels of NLB2-3 seemed to be at the cost of ewes' survival, even in the moderate flock environment. In conclusion, the flock environment influenced the level of early prolificacy beyond which ewe longevity was reduced. It is suggested that further selection for high and early prolificacy in NZ flocks is likely to impair ewes' lifetime productivity.

Background In most mammals, lactating mothers dramatically increase their food intake after parturition and reach a peak intake rate after a certain time while their offspring continue to grow. A common view, perpetuated by the metabolic theory of ecology, is that the allometric scaling of maternal metabolic rate with body mass limits the changes in energy intake and expenditure. Therefore these potential effects of metabolic scaling should be reflected in the elevation of maternal energy intake during lactation. To test this hypothesis, we collected published data on 24 species (13 domesticated) and established scaling relationships for several characteristics of the patterns of energy intake elevation (amplitude of the elevation, time to peak, and cumulative elevation to peak). Results A curvilinear allometric scaling relationship with maternal body mass (in double-logarithmic space) was found for the amplitude of maternal energy intake elevation, similarly to what has been observed for scaling relationships of basal metabolic rate in non-breeding mammals. This result indirectly supports the metabolic theory of ecology. However, this curvilinear allometric scaling does not seem to drive the scaling relationships found for the other characteristics of maternal energy intake. Both the duration and shape of the energy intake patterns showed substantial variation independently of species’ body mass. Conclusions Data available for a few mammals, mostly domesticated, provides little evidence for the hypothesis that a single law of metabolic scaling governs the elevation of maternal energy intake after parturition. Obtaining further food intake data in wild species will be crucial to unravel the general mechanisms underlying variation in this unique adaptation of mammalian females. Electronic supplementary material The online version of this article (doi:10.1186/s12983-016-0164-y) contains supplementary material, which is available to authorized users.

This study aimed to characterize the time-profile of extended lactation (EL) for dairy goats, and the relationships between milk production, liveweight, and intake that are associated with this profile. For this, 20 nonpregnant multiparous dairy goats were monitored daily for about 90 d from the onset of EL [i.e., when an increase in milk yield (MY) was observed]. These 20 individual profiles were pooled to create a group average profile at the onset of EL for the purpose of parameterizing a simple compartmental model. Moreover, 9 of the 20 EL goats were kept to compare their 24-mo profiles of body weight and milk production with those observed during 2 successive normal lactations (NL). Despite being kept in the same environment and on the same feed, a clear change from decreasing to increasing MY was identified (time of change, T-change) for all of the 20 EL goats around 330 d in milk. During the whole 24-mo period, EL goats produced as much milk as NL goats but this total milk production was unequally split before (56%) and after (44%) T-change. In terms of body weight, the most striking difference between EL and NL goats was the rapid and very high increase (+9.3 kg with an average daily gain of 60.4 g/d) that was observed concurrently with the increase in MY. Model parameterization with the group average profile does not support that the rise in MY drives the increase in resource acquisition as is generally assumed at the onset of an NL. Rather, it demonstrates that the transfer of energy from feed to milk is delayed at the onset of EL. Moreover, assessing the model ability to fit the range of individual profiles showed that the performances over the first 90 d of EL are largely predetermined by the animal state at T-change. The analysis of individual variability in EL efficiency showed that it depends both on an increase in resource acquisition and on the potential of goats to partition energy from the diet toward milk production instead of to body tissue gain. Finally, predicting the suitability for EL requires the consideration of more than just milk production for 300 d in milk.