Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 9, 2003
Publication Date: September 1, 2003
Repository URL: http://ars.usda.gov/SP2UserFiles/Place/54340000/Publications/geneticevaluationofanindexofbirthweight.pdf
Citation: MACNEIL, M.D. 2003. GENETIC EVALUATION OF AN INDEX OF BIRTH WEIGHT AND YEARLING WEIGHT TO IMPROVE EFFICIENCY OF BEEF PRODUCTION. JOURNAL OF ANIMAL SCIENCE 81:2425-2433. Interpretive Summary: The objectives of this research were to estimate genetic parameters for weight traits of CGC and to evaluate genetic responses resulting from selection based on the index: I = 365-d weight minus 3.2(birth weight). Results demonstrate that despite a genetic antagonism that compromises selection response for reduced birth weight and increased postnatal growth, significant favorable genetic responses can be achieved. Selection for the index had a favorable effect on the shape of the growth curve, restricting response in birth weight and mature weight of cows. Selection intensity in this experimental setting would be reduced relative to that which would be available across a breed using national cattle evaluation and AI. Thus, to the extent that selection against birth weight and for greater subsequent growth increases efficiency of beef production, seedstock producers have even greater potential to make progress than can be demonstrated in a research setting.
Technical Abstract: The CGC population is a stabilized composite of 1/2 Red Angus, 1/4 Charolais, and 1/4 Tarentaise germplasm. The objectives of this research were to estimate genetic parameters for weight traits of CGC and to evaluate genetic responses resulting from selection based on the index: I = 365-d weight minus 3.2(birth weight). Phenotypes evaluated were birth weight (n = 5,083), 200-d weight (n = 4,902), 365-d weight (n = 4,626), and the index. There were 1,433 cows with at least one recorded weight and 4,375 total observations. In 1989, a randomly selected control line and a line selected for greater values of the index were established. Average generation intervals were 3.16 +/- 0.04 yr and 3.90 +/- 0.08 yr in the index and control lines, respectively. The index selection line (n = 950) accumulated over three generations approximately 212 kg more selection differential than the control line (n = 912). Heritability estimates for direct effects were: 0.32 +/- 0.04, 0.49 +/- 0.05, 0.49 +/- 0.05, 0.30 +/- 0.04, and 0.70 +/- 0.04 for the index, birth weight, 365-d weight, 200-d weight, and cow weight, respectively. Heritability estimates for maternal effects were: 0.05 +/- 0.02, 0.11 +/- 0.03, 0.04 +/- 0.02, and 0.19 +/- 0.04 for the index, birth weight, 365-d weight, and 200-d weight, respectively. In the control line, direct genetic changes for the index and its components were small. For the index selection line, direct genetic changes for the index, birth weight, 365-d weight, 200-d weight, and cow weight were 6.0 +/- 0.3, 0.45 +/- 0.09, 7.74 +/- 0.55, 3.42 +/- 0.25, and 6.3 +/- 0.9 kg/generation, respectively. Maternal genetic changes were generally small for both the control and index selection lines. Thus, selection for the index produced positive correlated responses for direct genetic effects on body weight traits at all ages with only minor effects on maternal genetic effects. Results demonstrate that despite a genetic antagonism that compromises selection response for reduced birth weight and increased postnatal growth, favorable genetic responses can be achieved.