|Chase, Chadwick - Chad|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/18/2000
Publication Date: 12/1/2000
Interpretive Summary: Selection decisions for replacement heifers and bulls are usually made at 12 to 18 mo of age. For early selection decisions to be effective, reliable estimates of genetic parameters for associated traits measured at young and older ages and their genetic relationships are needed. Matching beef cattle types to their environment is critical and an important component includes body size. Common measures of body size include weight and hip height. Perhaps a multiple trait evaluation that includes both hip height and body weight would be a better option for selection of body size than either trait alone. Genetic parameters for weaning hip height (WHH), weaning weight (WWT), postweaning hip height growth (PHG), and hip height at 18 mo of age (HH18) and their relationships were estimated using Brahman cattle born from 1984 to 1994 at the STARS. Results indicated that there was a strong genetic relationship between WHH and WWT that has an impact on HH18, ,a common age for replacement heifer and bull selection. Relationships between estimated breeding values for WHH, WWT, and HH18, indicated that animals could be identified that would reduce, maintain, or increase hip height while weaning weight was increased. Thus, if the breeding objective is to manipulate growth to 18 mo age, implementation of multiple trait breeding programs that consider hip height and weight at weaning will help to predict hip height at 18 mo age.
Technical Abstract: Genetic parameters for weaning hip height (WHH), weaning weight (WWT), postweaning hip height growth (PHG), and hip height at 18 mo of age (HH18) and their relationships were estimated for Brahman born from 1984 to 1994 at the STARS. Records per trait were 889 WHH, 892 WWT, and 685 HH18. Variances and covariances were estimated using REML fitting three two-trait tmodels (i.e., WHH-WWT, WHH-PHG, and WWT-HH18). Heritability estimates were .73 and .65 for WHH direct, .29 and .33 for WWT direct, .10 and .09 for WHH maternal, .18 and .18 for WWT maternal, .00 for PHG maternal, and .03 for HH18 maternal. Genetic correlation estimates between the direct effects for the different traits were moderate and positive, and were positive between WHH and WWT maternal and WWT and HH18 maternal, but was negative (-.19) between WHH and PHG maternal. Negative genetic correlations existed between direct and maternal effects for WHH, WWT, PHG, and HH18. Correlation between WHH direct and WWT maternal effects was low and negative, was moderate and negative between WHH direct and PHG maternal, and was high and negative (-.80) between WWT direct and HH18 maternal. Results indicate that there is a strong genetic relationship between hip height and weight at weaning that has an impact on hip height measured at 18 mo age, a common age for bull and heifer selection.