The Effect of Sex on the Development of the Pig

Abstract

Data on the growth rates of 1602, pigs from seven Poland China lines and 795 from the Minnesota No. 1 line were utilized in a comparative study of gilts and barrows. The estimated sex difference in rate of growth from weaning to 200 pounds was .039 pounds per day in the Poland Chinas and .089 in the No. 1 line. The two were significantly different. The contrast is believed due to earlier expression of sex in the No. 1 line. The sex difference is large enough at least in the Minnesota No. 1 line so that it should be considered in progeny comparisons. There was no indication of non-random variation in the sex differences within the Poland Chinas; none of the interactions involving sex were significant. A sex-sire interaction, significant at the five per cent level, suggests the presence in the No. 1 line of a segregation of genes concerned with the effect of sex on the growth rate. The sex difference in growth rate increased with age in both groups. However, the increase was significantly greater in the No. 1 line. The analysis of sex differences by periods in the No. 1 line revealed a significant period-year interaction that appeared to be the result of a shift in the age at which the greatest sex difference occurred. Implications regarding the effect of selection for growth rate on age of puberty were discussed.