|Mousa, E. - FAC. OF AGRIC., EGYPT|
|Van Vleck, Lloyd|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 25, 1999
Publication Date: N/A
Interpretive Summary: Interpretive Summary Lamb weight and daily gain are important components of market lamb production. One way to increase meat output or achieve rapid growth and heavy market weight is by using terminal sire breeds. A composite population of sheep was formed at the U.S. Meat Animal Research Center to produce such a terminal sire line. For genetic evaluation and selection, genetic parameters for traits of importance should be known. The objective of this study was to estimate variances and covariances due to direct genetic, maternal genetic, and permanent maternal environmental effects for five growth traits recorded on this composite population. Heritabilities were large enough that selection would be effective for improving any of the growth traits. Selection for larger weaning weight would need to consider maternal genetic and permanent maternal environmental effects as well as the negative genetic correlation between direct and maternal effects. Estimates of genetic correlations show that selection for weaning weight would also increase birth weight and would also increase weight at 19 and 31 months and by implication mature weight. Similarly, selection for gain from 9 to 18 weeks of age would be effective and not complicated by maternal effects. Such selection would be likely to increase mature weight and have little effect on birth weight. The genetic correlation between average daily gain in females and males of .94 indicates selection based on gain in either sex would be effective for improving gain in both sexes.
Technical Abstract: Records of 9,055 lambs from a composite population originating from crossing Columbia rams on Hampshire by Suffolk cross ewes at U.S. Meat Animal Research Center were used to estimate genetic parameters among growth traits. Traits were weights at birth (BWT), weaning (7 wks, WWT), 19 months (W19), 31 months (W31) and postweaning average daily gain (ADG). Daily gain was divided into gain of males (DGM) and of females (DGF). (Co)variance components were estimated with REML for a model that included fixed effects of sex, age of dam, type of birth or rearing and contemporary group. Random effects were direct and maternal genetic of animal and dam, permanent maternal environmental, and random residual. Estimates of direct heritability were .09, .09, .35, .44, .19, .16, and .23 for BWT, WWT, W19, W31, ADG, DGM, and DGF. Estimates of permanent maternal environmental variance as a proportion of phenotypic variance were small. Estimates of maternal heritability were .17 and .09 for BWT and WWT and .01 to .03 for other traits. Genetic correlations were large among W19, W31, and ADG (.69 to .97), small between BWT and W31 or ADG, and moderate for other pairs of traits (.32 to .45). Estimate of genetic correlation between DGM and DGF was .94. Genetic correlations of DGM and DGF with W19 were .69 and .82 and with W31 were .67 and .67 which show that selection for ability to gain would increase mature weight. Models for genetic evaluation for BWT and WWT should include maternal genetic effects. Estimates of genetic correlations show that selection for ADG in either sex can be from records of either sex and that selection for daily gain will result in increases in mature weight but that BWT is uncorrelated with W19 and W31.