Factors affecting boar reproduction, testis function, and sperm quality

Abstract

Sperm quality of boars depends on both intrinsic (genetic) factors and extrinsic (environmental/husbandry) factors. In relation to intrinsic factors, an increased reproductive efficiency of crossbred boars as compared with purebreds manifests the importance of heterosis in this context. Studies on semen traits have demonstrated that some parameters have greater heritability than others, such as semen volume. At the same time there is a poor relationship between seminal parameters and fertility that limits the sensitivity and specificity of cut-off values based on these traits to select boars. Recent studies have pointed out the importance of selecting high-fertility boars according to their testis size at pre-pubertal age. Genetic defects in testicular size and structure, such as in cases of cryptorchidism, result in partial or total arrest of spermatogenesis at post-pubertal age. In relation to extrinsic factors, the ambient temperature, photoperiod, and rhythm of semen collection are negatively correlated with the reproductive performance of boars, whereas food supplementation, social contact with other pigs and the accuracy of semen processing protocols are positively correlated with artificial insemination (AI) outcomes. Certain divergences in the effects of these factors on individuals could be mainly attributed, although not exclusively, to the nature of the breed.