Effect of selection for lean growth on gonadal development of commercial pig genotypes in South Africa

Abstract

A primary objective of commercial pig production is lean meat yield in order to satisfy consumer needs. The majority of the commercial pig breeds in South Africa have been selected for high lean growth potential and reduced backfat thickness. There are indications that selection for high lean meat yield may affect the gonadal development and possibly reproductive potential of commercial pig genotypes, because both testicular and ovarian growth appear to be important indicators of reproductive performance in boars and gilts, respectively. The effects of selection for lean growth on gonadal development were studied in five South African commercial pig genotypes (1, 2, 3, 4 and 5) from 116 to 214 days of age. Gonadal growth and development were measured and compared in 112 gilts and 112 boars. Differences between means were tested using genotype and age as fixed effects, while the relationships between gonadal parameters were evaluated by means of correlation analysis. Gilts from genotype 1 had a significantly shorter ovary length than those from genotypes 2 and 3. Gilts from genotype 3 also had heavier ovaries and larger ovary volumes than gilts from genotype 1. However, genotype did not influence ovary width or height. Correlations between P2 backfat thickness and gonadal development were generally poor in gilts. In boars, genotype 3 had significantly heavier testes than boars from genotype 1. Testes volume of genotype 1 also tended to be smaller compared to genotype 3. Correlations between gonadal measurements and P2 backfat thickness of boars were positive and moderately high (0.560 ≤ r ≤ 0.587). It is concluded from the study that there are differences between commercial pig genotypes in terms of gonadal development. These results suggest that selecting against backfat thickness may delay gonadal development and sexual maturation in boars, while the results are not conclusive in sows.

Keywords: Pig; growth; backfat thickness; gonadal development; reproduction

South African Journal of Animal Science Vol. 36 (5) 2006: pp.26-29