Effect of competition on gain in feedlot bulls from Hereford selection lines

¹ Roman L. Hruska U.S. Meat Animal Research Center, Clay Center, NE 68933; Department of Animal Science, University of Nebraska, Lincoln 68583-0908
² Roman L. Hruska U.S. Meat Animal Research Center, Clay Center, NE 68933
³ Department of Animal Science, University of Nebraska, Lincoln 68583-0908

^* To whom correspondence should be addressed. E-mail: lvanvleck{at}unlnotes.unl.edu.

	Abstract

This study examined competition effects on average daily gain in the feedlot of 1,882 Hereford bulls representing eight birth years from a selection experiment. Each year, eight feedlot pens were used to feed bulls in groups with two pens nested within each of the four selection lines. Gains were recorded for up to eight periods of 28 d. Models for analyses included pen effects (fixed or random), fixed effects such as year and line, and random direct genetic, competition genetic (and in some analyses competition environmental effects) and environmental effects. Each pen mate as a competitor affects records of all others in the pen. All lines traced to common foundation animals so the numerator relationships among and within pens were the basis for separating direct and competition genetic effects and pen effects. For this population and pen conditions (average of 30 bulls per pen), major results were: 1) competition genetic effects seemed present for the first 28 d period but not for the following seven periods, 2) models with pens considered fixed effects could not separate variances and covariance due to direct and competition genetic effects, 3) models without competition effects had large estimates of the variance component due to pen effects for gain through eight periods, and 4) models with both genetic and environmental competition effects accounted for nearly all of the variance traditionally attributed to pen effects (even though estimates of the competition variance component were small, the estimates of pen variance were near zero).

Key Words: average daily gain, beef cattle, competition effects, genetic effects