Breeding for reduced seasonal infertility and reduced response to heat stress in sows and boars

Abstract

This paper describes the impact of heat and seasonal stressors on the reproductive performance of pigs, management strategies to alleviate this impact and the opportunity to breed for pigs with increased ability to cope with seasonal stressors. The climate in Australia has become hotter. Currently, in Corowa NSW, there are about 40 days with a maximum temperature of above 35 °C during the year. This is a challenge for the pig industry due to pigs’ limited ability to regulate their body temperature. In sows and boars, heat stress has been identified as a factor contributing to reduction in reproductive performance over the summer/autumn period, known as seasonal infertility. Seasonal infertility is also due to changes in photoperiod and may be alleviated or elevated by multiple stressors such as heat stress, social stress or handling stress. Pig producers implement management strategies to alleviate the impact of heat stress on seasonal infertility. However, these management strategies may not eliminate all heat stress experienced by pigs. Therefore, selection for increased heat tolerance and reduced seasonal infertility of pigs will improve welfare and productivity of pigs. Genetic strategies require traits that describe seasonal infertility in boars and sows, that are of economic importance and that have genetic variation. Evidence for genetic variation in farrowing rate in response to ambient temperature (Bloemhof et al., 2008) and in response to ambient temperature and change in daylight (Sevillano et al., 2016) have been found. Despite the prominent role of farrowing rate to quantify seasonal infertility, other sow and boar traits to describe heat stress and seasonal infertility also have a genetic basis. A range of traits recorded in sows and boars should be explored to enable the development of selection strategies to reduce heat stress and/or season infertility in pigs.