Genetic correlations between ewe reproductive and lamb weight traits in D’man sheep

The objective of this study was to estimate genetic, phenotypic and residual correlations between ewe reproductive and lamb weight traits in D’man sheep. Data used in this study were 1804 reproductive and weight records collected between 1988 and 2015 from 530 replacement females, born from 82 sires and 298 dams. The ewe reproductive traits included litter size and litter weight at birth (LSB and LWB) and at 90 days (LSW and LWW) per ewe lambing and mating weight (MW), while the lamb weight traits investigated were weights at birth (BW), 90 (WW) and 135 (W135) days. Covariance components between the reproductive traits on the one hand and the weight traits on the other hand were estimated using bivariate analyses by employing the animal model that was deemed to be most appropriate from the univariate analyses for each trait. The genetic correlations between litter traits and body weights were low and in general not significantly different from zero ranging from -0.12 to 0.11, whereas those between ewe MW and lamb weights were positive and moderate varying from 0.16 to 0.51. The corresponding phenotypic correlations were slightly lower and varied from -0.04 between LSW and WW to 0.12 between LWW and BW and between LSW and W135. The residual correlations were in general similar to genetic correlations, except those between MW and body weights that were lower. It was concluded that selection for a genetic improvement in either of reproductive and weight traits would have little effect on genetic response in the other trait.