FACTORS AFFECTING GESTATION LENGTH IN THE PIG

Abstract

The effects of a number of factors on gestation length were examined in two groups of swine. The first group consisted of a Lacombe line (L) selected for post-weaning average daily gain (ADG), a control-Yorkshire (Y) line and a group of Yorkshire females (Y1) bred to Lacombe boars to produce L × Y litters. The second group of females were from twice-yearly farrowings following termination of the selection study. The effect of litter size, although statistically significant for all breeding groups, was small. Litter weight had a small but significant effect for the L and Y breeds. Sex ratio of the litter had no effect on gestation length. Consistent with previous results, the Lacombe was found to have a longer gestation length than the Yorkshire. When age effect was taken into account there was a small but significant parity effect between first and second litter. The effect of sow body weight at breeding (BW), body weight change during gestation (GWG), and weight change expressed as a proportion of breeding weight (RATIO) were examined in the group II females. A small but significant effect of RATIO was found in the Lacombe breed. There was found to be no sex effect on litter size. Heritability estimates for gestation length from daughter dam regression were 0.47, 0.72 and 0.69 for the L, Y and Y1 groups, respectively.