La perennite et la durabilite des elevages de ruminants dependent des capacites adaptives des femellesCoping abilities of the females and sustainability of ruminant livestock systems

摘要

From a systemic point of view, the breeder can be considered as the decisional component of the livestock farming system, whereas animals are usually depicted to be part of the biotechnical component. The animal itself can be considered as an autonomous biological system subjected to environmental constraints, whose abilities to survive, to grow, to reproduce and, finally to cope with the environnement and the livestock practices, play a major role in the ability of the livestock system to sustain. In such a conceptual representation of the system, the reproductive females play a major role as they determine in a great part the productivity and the durability of the system through their abilities to maintain their own production level (milk production, numeric productivity) and to save their reproductive efficiency (repeated pregnancies and lactations) over years. Considering the animal level and its lifespan, it is clear that the capacities to adapt rely on behavioural and physiological regulatory processes. Such processes are particularly revealed along studies in which biological mechanisms are involved to face the nutritional constraint (grazing behaviour, body reserves' dynamics). Focusing on the feeding constraint is quite interesting as regulatory processes implied in the energetic metabolism may interfere directly or indirectly with the reproductive function and thus, may play on the durability of the livestock system. A biological significance of such relationships between nutrition and reproduction is given that they allow the female to be informed about the associated risk of entering a productive process facing the uncertainty of the nutritional context. If the general mechanisms implied in the adaptability to cope with the underfeeding constraint are conserved in ruminants, the thresholds (or priorities) may largely differ according to the breed within the same species. Breeds are more or less able to cope with a new herd management or new nutritional conditions. In such a context, we point out that failures in reproduction, that might be interpreted by the breeder as an inability of the female to adapt, might have a sense on a biological point of view in regards to the adaptation to the nutritional risk. Hence, in order to evaluate the ability of the ruminants livestock farming systems to perpetuate in hard environments (maintaining their production levels) or to assess sustainable objectives (opening bushy landscapes by increasing grazing pressure), animals' inherent adaptive potentialities have to be well known.