Puberty and Estrus in Confinement-Reared Gilts

Abstract

The physiological mechanisms responsible for puberty in mammals remain poorly understood despite many investigations. The incidence of gilts that did not show regular estrous cycles at 9 months of age ranges from 10 to 40% and breed of gilt is an important factor contributing to this percentage. The percentage of Landrace gilts that showed regular estrous cycles at 6 months of age was higher (P<.01) than that of Hampshire, Large White, Yorkshire and Duroc gilts. Estrous activity for these five breeds of gilts at 8.5 months of age had reached a plateau and a higher percentage of Landrace, Large White, Hampshire and Duroc gilts showed regular estrous cycles than did Yorkshire gilts (78, 86, 71, 71 vs 56%, respectively). Of the noncyclic gilts slaughtered at 9 months of age, 55% were gilts with immature reproductive tracts (delayed puberty) and 45% were gilts with fully developed uteri and ovaries that had corpora lutea at different stages of development or preovulatory follicles and corpora albicans (behavioral anestrus). Behavioral anestrus can be reversed by methallibure treatment. Season of year and social environment, in addition to breed, influence puberty and regularity of estrous cycles in confinement-reared gilts, but the relative influence of each remains to be determined.