HERD OF ORIGIN EFFECTS ON THE PERFORMANCE OF STATION-TESTED BEEF BULLS

Abstract

Nine years (1976–1984) of performance data from the Manitoba Bull Testing Station, Douglas were used to investigate herd of origin effects on the 140-d growth performance of bulls. Two data sets were analyzed: the Angus and Hereford (AH) data set contained records on 1649 bulls; the Charolais and Simmental (CS) data set contained records on 1786 bulls. The mixed model for analysis of weight, gain and backfat data included year-breed as a categorical fixed effect, age of bull as a fixed covariate, and herd and sire as random effects in a hierarchial classification. Herd, sire and error components of variance were estimated for weights and gains of bulls during the test as well as for backfat which was measured at the end of the test. At the start of the test 39 and 33% of the variation among bull weights was due to herd of origin effects for the AH and CS data sets, respectively. This proportion dropped gradually to 30 and 22% at the 112-d weighing for the AH and CS data sets, respectively, and remained at these levels for the 140-d weights. For the cumulative 140-d gain on test only 15 and 16% of the total variation were attributed to herds for the AH and CS data sets, respectively. For periodic gains (gains made between two adjacent weighings, usually 28-d intervals), herd of origin was a major source of variation for the 28-d pretest adjustment period (45 and 34% for the AH and CS data sets, respectively), but was of minor importance in subsequent periods. For backfat, herd of origin was a significant though small source of variation. The nature of the herd of origin variation (genetic or environmental) could not be discerned from this analysis though it was evident that a portion of the herd of origin variation was temporary environmental in nature since its magnitude decreased as the test progressed. Assuming that a portion of the herd of origin variation was permanent environmental in nature for both weight and gain and given that herd of origin variation was lower for gain than for weight it is recommended to emphasize test gain as opposed to weight in the comparison of bull performance. Key words: Beef cattle, test station, herd of origin, heritability, growth, backfat