Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: March 6, 2008
Publication Date: July 23, 2008
Citation: Williams, C.B., Jenkins, T.G. 2008. Impact of simulated selection for feed efficiency and length of breeding season on beef life cycle performance [abstract]. Journal of Animal Science. 86(E-Supplement 2):254-255. Technical Abstract: The Decision Evaluator for the Cattle Industry (DECI) was used to simulate production for a base herd (BA), a herd in which genetically superior sires for feed efficiency were used (SA), and a herd in which genetically superior sires for feed efficiency and lower fertility were used (SB). Within each selection scenario, four breeding season lengths (BSL) were simulated, 90 d, 75 d, 60 d, and 45 d. Eight 15-yr-simulation runs were done for each selection by length of breeding season scenario. Animals were a composite of 50% Angus and 50% Simmental. Exposed females were palpated at weaning and open cows were culled at that time and replaced with pregnant heifers to maintain herd size at 150 calving females. At weaning all open and excess pregnant heifers were sold, and all steers and non-replacement heifer calves were put on a stocker program for 150 d to gain 0.91 kg/day, then finished on a high-concentrate diet (3.258 Mcal ME/kg DM). In each 15-year simulation, yearly production and financial data were collected and averaged over yr 14 and 15 to measure selection response relative to the BA. Compared to BA, ADG increased by 0.04 kg (P < 0.05) and feed efficiency increased by 0.02 (P < 0.05) in both SA and SB. Decreasing BSL from 90 to 45 d, required an increase of 15 female replacements to maintain herd size, and resulted in a greater proportion of steers to heifers going into the finishing phase and heavier average slaughter weights. Except for the 90-d breeding season, the impact of lower fertility sires was to increase the number of replacement females needed to maintain herd size by 2 in SB herds. Income over feed costs (IOFC) for the combined cow/calf and post-weaning phases was significantly higher in SA and SB and decreased as BSL decreased. These results show that selection for feed efficiency would increase post-weaning feed efficiency and IOFC by about 10 and 12% respectively, and have a small positive impact on ADG. Shorter BSL increased replacement rate and decreased IOFC.