Les méthodes de maîtrise de la reproduction disponibles chez les mammifères d'élevage et leur intérêt en agriculture biologique

Abstract

The control of reproduction is necessary to optimise the productivity of livestock production systems. The regulations of organic farming do not impose specific reproductive practices among those that are already in use except that some of them are not authorized. Whatever the animal species, the success of reproduction in organic systems mainly relies on the choice of adapted breeds. Because sheep and goats are well-known seasonal breeders the major issue is to overcome this limitation of reproductive possibilities. In these organic farming systems the reproduction is possible all year round thanks to the manipulation of daylight duration without using melatonin, however up to now these treatments are not developed. The male effect is another method to overcome seasonal blockade and that allows synchronizing lambing and kidding without any hormonal treatments. This method is however rather difficult to apply in all situations. Artificial insemination (AI) is the main way to benefit from selection's progress. In conventional systems AI is performed at fixed time after hormonal synchronization of ovulations without necessity to detect oestrus. AI, which is authorized on natural oestrus, is not really used in organic flocks because they are spread over several days. Synchronization of oestrus with the male effect is however a promising way to perform AI and allow organic breeders to benefit from selection schemes. In conventional swine production systems the classical practice is to drive sows into a 7 batches system at 3 weeks interval. The productive cycle duration is of 21 weeks including 28 days of suckling. In the European regulation of organic farming systems, the piglet suckling period should not be shorter than 40 days. Practically the weaning will occur at 42 days with a 8 batches system. Hence the whole productive cycle of the sow will be lengthened up to 23 weeks. In organic system, like in conventional systems, weaning is the main method to synchronize sows oestrus within a given batch. The overall efficiency of organic production is however reduced because no hormonal treatment is allowed either to synchronize gilts or to transfer open sows into another band and those that may show oestrus during lactation. In all pig production systems AI is performed after oestrus detection. In cattle, AI is generally performed after detection of natural oestrus. Reproduction is mainly performed through AI in dairy cows and with bull mating in beef cows. Thus the fact that hormonal treatments are not allowed in organic systems do not penalise them. Furthermore reproduction is possible all year round except that it is performed according to productive goals and local constraints. The development of natural methods for the control of reproduction in organic livestock systems implies numerous research approaches and multidisciplinary programs, often common to different species. INRA is strongly involved in the study of hormone-free methods and their adaptation to breeding constraints.