|Van Vleck, Lloyd|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/31/1999
Publication Date: N/A
Interpretive Summary: Previously animal breeders have had to assume that the same genes influence performance in different environments. For example, in this study the environments were defined by age of the dam when the lamb was born. Statistical techniques and computing capability now allow for testing that assumption. Weights of lambs at birth (BWT), weaning (WWT) and average daily gain from birth to weaning (ADG) of Columbia, Polypay, Rambouillet, and Targhee breeds were divided into measurements taken when dams of lambs were young (Y, 1 yr), middle aged (M, 2-3 yr) and older aged (O, >3 yr). Correlations among expressions of the same genotype when the dam was of different ages were estimated. If the correlation is greater than .80, the usual conclusion is that expression is similar enough that the assumption of same genes affecting performance in the two environments is adequate. The correlations across age classes of dams were similar for WWT and ADG. The estimates of correlations among expressions with different age classes of dams were small on average, only about .32 for BWT but were larger for WWT (.70). Correlations of expression of maternal effects across age classes were even smaller, averaging .36 or less. These results, although variable from breed to breed, suggest that genetic evaluation systems need to consider multiple trait evaluations with expression of weights as different traits when the dams are young and when the dams are older.
Technical Abstract: Correlations between genetic expression in lambs when dams were young (Y, 1 yr); middle aged (M, 2 and 3 yr); or older aged (0, > 3 yr were estimated with three-trait analyses for birth (BWT) and weaning (WWT) weights and average daily gain (ADG) from birth to weaning. Number of observations were 7,731; 9,518; 9,512; and 9,201 for Columbia (C), Polypay (P), Rambouillet (R), and Targhee (T) breeds of sheep, respectively. Relative estimates for WWT and ADG were similar when averaged across breeds. Estimates were variable across breeds. On average, direct heritability was greater when environment was young dams (.44 for BWT and .34 for WWT) than when environment was older dams (.20 for BWT and .18 for WWT). Maternal heritability was greater when dams were older, .25 vs .18 for BWT, but was greater when dams were younger, .10 vs .05, for WWT. The estimates of genetic correlations for direct effects across age of dam environments averaged .32 for birth and .70 for weaning weights. Estimates of maternal genetic correlations across age of dam classes were .36 or less for BWT and WWT. Total maternal effects accounted for .33 to .42 of phenotypic variance for BWT and for .09 to .26 of phenotypic variance for WWT. Average estimates of genetic correlations between expressions of same genotypes with different ages of dams suggest that measurements of BWT of lambs with dams in Y, M, and O age classes should be considered to be separate traits for genetic evaluation. For WWT, measurements with dams of Y and combined M and O age of dam classes should be considered to be separate traits for genetic evaluation.