Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/16/2005
Publication Date: 6/15/2005
Citation: Brown, M.A., Coleman, S.W., Lalman, D.L. 2005. Relationship of sire estimated progeny differences to milk yield in Brangus. Journal of Animal Science. 83:1194-1201. Interpretive Summary: Genetic improvements in calf weaning weights through improvement in milk production of the dam is important to efficiency of calf production in cow-calf enterprises. Sire estimated progeny differences (EPD) for milk are useful tools to predict differences in milk yield of their daughters and weaning weights of the progeny of their daughters for purposes of genetic improvement. However, research at the USDA-ARS Grazinglands Research Laboratory, El Reno, OK suggests that cows in excess of 500 kg may not always express their genetic potential for milk yield and calf weaning weight when managed under extensive grazing conditions on forages common to the Southern Great Plains. It is possible that heavier cows may be diverting forage nutrients to maintenance of their greater body weight at the expense of milk production. This, in turn, suggests that there may be practical maximum sire milk EPD for larger cows in specific production environments, above which, little benefit will be seen in either milk yield or calf weaning weight by selection of sires with the higher milk EPD. Thus, there is a need to match both genetic potential for mature weight and genetic potential for milk yield and calf weaning weight with specific production environments to maximize efficiency of calf production.
Technical Abstract: Milk yield from 160 Brangus cows sired by 65 Brangus bulls was measured over a period of three years using a single-cow milking machine to estimate the relationship of sire estimated progeny differences for milk with actual milk yield of their daughters and calf weights during the preweaning period. Milk yield was estimated six times per year at an average 49, 78, 109, 138, 168, and 198 d postpartum. The relationship of sire milk EPD to milk yield of their daughters was quadratic (P < 0.01) and the linear portion of the curve differed among months (P < 0.05) at an average cow weight. However, the relationship was largely linear in cows weighing 500 kg or less and curvilinear in cows weighing more than 500 kg. Similarly, the regression of average daily milk yield and total 205-d milk yield were curvilinear (P < 0.10). The relationship of grandsire milk EPD to calf weight was quadratic (P < 0.01) with a trend for the quadratic portion of the curve to differ with month of lactation (P = 0.15) and evidence for monthly differences in the linear component of the equation (P < 0.01). A trend existed for the relationship of grandsire milk EPD with calf 205-d weight to be curvilinear (P < 0.19). However, the relationship of calf 205-d weight to milk yield of their dam was linear (P < 0.01). Results from these data suggest that genetic potential for milk yield and associated effects on calf weight transmitted through the sire may have a practical maximum due to nutritional limitations that prevent expression of genetic potential beyond that level, particularly in heavier cows. Thus, there is a need to match both genetic potential for mature weight and genetic potential for milk yield and calf weaning weight with specific production environments.