Date of this Version
Litter data from two crossbreeding experiments were used to estimate coefficients for regressing 21-day litter weight on litter size at 21-days. Exp. 1 involved 1,003 purebred and Fg gilts of Hampshire, Duroc and Yorkshire breeding and 206 second parity sows of Duroc, Hampshire and Yorkshire breeding; Exp. 2 involved 388 F1 gilts and sows of Duroc, Yorkshire, Landrace and Spot breeding. The linear and quadratic regression coefficients from the gilt data in Exp. 1 were 5.64 ± .29 kg/pig and -.10 ± .02 kg/(pig)2, respectively. For Exp. 2, the regression coefficients were 5.98 ± .71 kg/pig and -.14 ± .05 kg/(pig)2. In both data sets, there was less than a .5% reduction in r 2 when the model was reduced from a linear and quadratic to a linear equation. The linear regression coefficients were 4.28 ± .07 kg/pig and 3.91 ± .14 kg/pig in Exp. 1 and 2, respectively. The linear and quadratic regression coefficients from sow data in Exp. 1 were 6.28 ± .55 kg/pig and -.14 ± .04 kg/(pig)2. When the model was reduced to a linear model, there was a significant interaction between breed of dam and the linear regression coefficient. These regression coefficients were 4.74 ± .25 kg/pig for Duroc, 4.73 ± .26 kg/pig for Hampshire and 3.55 ± .30 kg/pig for Yorkshire. Breed of dam differences for gilt 21-day litter weight adjusted to constant litter size were significant in Exp. 1. Duroc dam litters weighed less than litters of Hampshire, Yorkshire and the F1 crosses. In Exp. 2, breed of dam differences were not significant for F1 crossbred females of Duroc, Yorkshire, Landrace and Spot breeding, and litters from second parity sows weighed 7.37 ± .71 kg more than gilt litters when adjusted to a constant litter size.