Metabolic status and reproduction in the lactating sow

Abstract

Many sows are submitted to a nutritional deficiency during lactation because of high nutrient requirements and insufficient feed consumption. When the nutritional deficiency is severe, it can result in a delayed oestrus after weaning, especially in young sows. Ovulation rate after weaning can also be altered. The same consequences are observed when sows are restricted only in energy or dietary protein. The consequences of the nutritional deficiency may be attenuated when sows have large body reserves in early lactation.

The delay of oestrus and ovulation after piglet weaning is mainly due to the inhibition of the episodic secretion of hypothalamic GnRH during lactation. In contrast, the reduction in ovulation rate may occur independently of changes in gonadotropin secretion, suggesting the existence of direct effects at the ovarian level. This review analyses the physiological mechanisms by which information on the metabolic changes is transmitted to the hypothalamus-pituitary-ovary axis. The availability of oxidisable metabolic fuels, such as glucose, could be the first signal informing the hypothalamus of the metabolic status. Insulin could play a role in modulating the availability of glucose in brain cells. The role of leptin and IGF-I on GnRH secretion during lactation has not yet been established in the sow. Lastly, some amino acids are necessary for the synthesis of neurotransmitters involved in the secretion of GnRH; a reduction in their availability could be involved in the inhibition of GnRH secretion during lactation. At the ovarian level, folliculogenesis is likely to be altered by the reduction in insulin and IGF-I concentrations induced by the nutritional deficiency. The influence of other factors, such as the availability of some amino acids, must not be ruled out.