Age at Puberty and Related Phenomena in Outbred Chester White and Poland China Gilts

Abstract

Data on age at puberty are presented on 49 Chester White and 37 Poland China gilts. There was not a significant difference in age at puberty between these two breeds but the Poland Chinas were significantly heavier at puberty than the Chester Whites. Length of the first estrual cycle was more variable in Chester Whites than in Poland Chinas. Chester White gilts ovulated a significantly greater number of eggs at first and second heat periods than did the Poland Chinas. Within each breed the increase of second ovulation over the first was highly significant. Neither age nor weight at first or second heat periods was closely associated with ovulation rate. In each of these breeds, the left ovary ovulated more eggs than did the right ovary. Fertilization rate was higher and embryonic death rate was lower in Chester Whites than in Poland Chinas. Average size of litter farrowed was 10.27 for Chester White and 6.48 for Poland China. Gilts born later in the farrowing season tended to reach puberty at a younger age. It was not possible to predict age at puberty in these animals from a knowledge of body weight with any greater accuracy at one age than at any other age.