The sex ratio of a gilt’s birth litter can affect her fitness as a breeding female

Abstract

Lifetime reproductive performance and behaviour are established in utero driven by genetics and the steroidal milieu of the uterine environment. Developing males synthesise androgens that can be absorbed by females in the litter. Consequently, the proportion of males in a litter has the potential to affect both lifetime reproductive performance and behaviour of female littermates. Although reproductive potential is understandably important for gilt selection, behaviour is becoming progressively more important as group housing of sows increases. Aggression can be a cause for removal from the breeding herd, and can also negatively affect reproductive performance and herd longevity. This review covers existing evidence of masculinisation in rodents and sheep, the mechanism causing masculinisation, and the knowledge gaps surrounding masculinisation in pigs. Premature culling of gilts is an economic and animal welfare issue in the pork industry resulting in low retention of gilts and reduced productivity. The selection of gilts needs to be improved to incorporate both lifetime reproductive potential and behaviour. We determined that there is cause to investigate the effect of the birth litter sex ratio of a gilt on her suitability for selection into the breeding herd.