Seasonal variation of reproductive performance of the sow

Abstract

The sow is not a seasonal breeder. However, reproductive performance decreases during summer and early fall in many countries. The proportion of sows with a delayed oestrus after weaning increases and the proportion of inseminated sows that do not farrow is reduced by 5 to 15 %. Pregnancy failure is largely due to abortion. Reproductive dysfunction can be associated to a higher culling rate, especially for young sows.

The influence of season is mainly attributed to photoperiod and ambient temperature. The daily light duration is perceived by the sow through melatonin secretion by the pineal gland, as in all seasonal breeders. However, the link between melatonin and LH secretion has not been demonstrated yet in the sow. Heat stress can alter embryo survival in early gestation through sow hyperthermia. During lactation, sows adapt to high temperatures by reducing feed intake and adjusting metabolic and endocrine status. Nutritional deficit is known to increase the risk of anoestrus after weaning. Physiological adaptations to heat stress are likely to play also a role.