Efficacité des traitements de synchronisation des chaleurs chez les bovins

Abstract

In France, three types of hormonal treatments are used to synchronise oestrus in cattle. They are based on the utilisation of prostaglandins F 2α or analogs (PGF2α at 11-14 day intervals), on the association GnRH and PGF2α (GnRH, PGF2α on D7, GnRH on D9) and on the association progestogen (during 9 to 12 days) and oestrogen with or without PGF2α and/or eCG. Prostaglandin F2α induces luteolysis and oestrus in spread over several days. Insemination at observed oestrus is more effective than systematic insemination 72 and 96 hours after the second injection of PGF 2α. The associations of GnRH/PGF2α and progestogen/oestrogen/PGF2α/eCG act on both follicular growth and luteolysis. The induced heats are well-grouped and it is possible to use systematic insemination. Based on their mechanisms of action, the first two treatments should be reserved for cycling animals, whereas the third treatment based on progestogens can be used on anoestrus females. Fertility at induced oestrus is variable, and ranges from 20 to 70% in large groups of animals. Some variation factors are known but cannot be controlled by current reproduction practices (day of the cycle at the moment of treatment, cyclicity before treatment, calving rank, calving conditions, body condition score ...). Others can be used to improve fertility in animals which have reproductive difficulties (lengthen the period between calving and treatment, use of flushing, temporary separation of the calf in beef cows). Thus, adequate knowledge of the physiological mechanisms governing the effect of each treatment, an evaluation of risk factors seen in synchronised animals and the application of corrective measures should allow the treatment to be adapted to the different situations encountered in the field and therefore improve fertility and reduce its variability.