Hormonal control of reproduction in small ruminants.

Reproduction of small ruminants can be controlled by several methods developed in recent decades. Some of these involve administration of hormones that modify the physiological chain of events involved in the sexual cycle. Methods which utilise progesterone or its analogues are based on their effects in the luteal phase of the cycle, simulating the action of natural progesterone produced by the corpus luteum after ovulation, which is responsible for controlling LH secretion from the pituitary. Use of prostaglandins is an alternative method for controlling reproduction by eliminating the corpus luteum and inducing a subsequent follicular phase with ovulation. Finally, the discovery of the properties of melatonin in photoperiod-dependent breeding animals opened up a new methodology to control reproduction in these species, inducing changes in the perception of photoperiod and the annual pattern of reproduction. Use of hormones to induce oestrus has allowed increased use of artificial insemination in small ruminants, a very useful management tool, considering the difficulty of detecting oestrus in these species. At commercial level, synchronisation of oestrus allows control of lambing and kidding, with subsequent synchronisation of weaning of young animals for slaughter. Also, it allows more efficient use of labour and animal facilities. Multiple ovulation and embryo transfer programmes are also possible with the use of oestrus synchronisation and artificial insemination. Finally, hormonal treatments have also been used to induce puberty in ewe-lambs and doelings.