Department of Animal Science


Date of this Version



Published in Livestock Science 102 (2006) 72–82.


The objective was to describe genetic parameters and genetic changes in litter sizes at birth and weaning (LB and LW, n =9081), birth weight (BW, n =11,896), weaning weight (WW, n =11,104), fleece weight and grade (FW and FG, n =8872), and staple length (SL, n =1805) of Polypay sheep. Direct heritability estimates from single-trait analyses were 0.11 for LB, 0.02 for LW, 0.17 for BW, 0.18 for WW, 0.68 for FW, 0.36 for FG, and 0.76 for SL. Estimates of direct genetic correlation were 0.40 between LB and LW, 0.57 between BW and WW, 0.65 between FW and SL, -0.37 between FW and FG and -0.70 between SL and FG. Breeding values (BV) from both single-trait and seven-trait analyses calculated using the parameters estimated from single-trait and two-trait analyses were compared across years of birth with respect to genetic trends. Estimated BV from both analyses for LB, LW, BW, WW and FW increased over time, while those for FG and SL were unchanged. Estimated changes in BV over time did not differ substantially for single-trait and seven-trait analyses, except for traits highly correlated with another trait that was responding to selection (i.e., LB, which was highly correlated to both LW and WW).