Author
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Macneil, Michael |
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MOTT, THOMAS - MAES |
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Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 1/20/2006 Publication Date: 6/1/2006 Citation: Macneil, M.D., Mott, T.B. 2006. Genetic analysis of gain from birth to weaning, milk production and udder conformation in line 1 hereford cattle. Journal of Animal Science 84:1639-1645. Interpretive Summary: The maternal effect on preweaning gain of beef calves is thought to arise from differences in milk production of cows. Yet, there is an inherent distrust among some farmers and ranchers of statistically derived predictions of maternal genetic effects on preweaning gain. Further, a concern exists about whether or not selection for increased milk production leads to a deterioration of udder quality and as a result reduces herd life of the beef cow. Thus, this research sought to validate the utility of maternal genetic effects on preweaning gain as an indicator of milk produced and to evaluate the genetic and phenotypic relationships between milk production and udder conformation. The research made use of data from the Line 1 Hereford population maintained by USDA-ARS at Miles City, Montana. Phenotypic variation in preweaning gain of calves, and milk production and udder conformation scores of cows was partitioned into genetic and environmental components. A very strong genetic relationship was detected between the maternal genetic effect on preweaning gain as a trait of the calf and milk production as a trait of the cow. Similar mildly antagonistic genetic associations of maternal genetic effect on preweaning gain and milk production with udder conformation score were also found. However, this correlation is not so strong as to preclude simultaneous improvement of milk production and udder quality using appropriate breeding values for each trait. This information is useful to seedstock producers as they design breeding programs to improve maternal qualities of their cattle. Technical Abstract: The objective of this research was to partition phenotypic variation in calf gain from birth to weaning, and milk production measured by the weigh-suckle-weigh method and udder score of cows into genetic and non-genetic components. Data were from the Line 1 Hereford population maintained by USDA-ARS at Miles City, Montana. Data collected through 2005 included 6835, 692, and 1686 observations of preweaning gain, milk production and udder score, from 2172, 403 and 622 dams and cows since 1935, 1994 and 1995, respectively. Data were analyzed using a Gibbs sampler for multiple-trait animal models. A burn-in of 10,000 rounds, 200,000 rounds of post-burn-in Gibbs sampling, and a thinning interval of 200 rounds were used for the final analysis. All results are reported as mean ± SD derived from the posterior distribution of parameter estimates. Mean estimates of the phenotypic variance of preweaning gain, milk production, and udder score were 476.3 kg2, 8.88 kg2, and 1.89 (1-9 scale), respectively. Estimates of phenotypic correlations between preweaning gain and milk production, preweaning gain and udder score, and milk production and udder score were 0.37± 0.04, -0.07± 0.04, and -0.09± 0.05, respectively. Estimates of heritability for direct and maternal preweaning gain, milk production, and udder score were 0.13 ± 0.03, 0.25 ± 0.04, 0.25 ± 0.06 and, 0.23 ± 0.05, respectively. Genetic correlations of milk production with maternal preweaning gain and udder score were estimated as 0.80 ± 0.08 and -0.36 ± 0.16, respectively. Estimates of the other genetic correlations were not different from zero (P > 0.05). Estimates of repeatability of maternal preweaning gain, milk production and udder score were 0.43 ± 0.03, 0.39 ± 0.05 and 0.34 ± 0.03, respectively. Breeding value for maternal gain from birth to weaning was highly predictive of breeding value for milk production and selection based on the former breeding value may be nearly as effective in changing milk production as direct selection on the latter. A potentially undesirable consequence of selection to increase milk production is the degradation of udder quality. However, this correlation is not so strong as to preclude simultaneous improvement of milk production and udder quality using appropriate breeding values for each trait. |
