Seasonality of reproduction in gilts and sows.

Abstract

In the wild, the pig adapts her reproductive functions according to the seasonal changes in the environment, such as the ambient temperature and availability of food. Like in other short day seasonal breeders, breeding season is favoured in the mid winter in order to provide the offspring with the best chances to survive four months later. Seasonal changes in environment are perceived mainly by the ability of the pig to recognise seasonal changes in photoperiod. This information is mediated through changes in the activity of the pineal gland to secret melatonin, essentially by the same mechanism as reported for other mammals. Stimulation of melatonin receptors located in the hypothalamus has a significant role for the release of GnRH and subsequent gonadotrophin release from the pituitary. Management and nutrition related factors determine the degree of seasonal effects on reproduction in the commercial piggery environment. Significant improvements in fertility in herds suffering from seasonal infertility are achievable by providing gilts and sows with abundant feed after mating. Attempts to alleviate the seasonal effects on fertility by applying light programs are underway and may lead to significant improvements in productivity of the domestic pig in the long run. Hormonal treatments may be somewhat effective, but not a sustainable solution to seasonal infertility. In conclusion, seasonal infertility is a photoperiod induced phenomenon that can be manipulated by changes in photoperiod and by accounting for season as a significant factor when feeding strategies are applied in commercial piggeries.