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Factors Affecting Test Performance of Beef Bulls¹

Virginia Polytechnic Institute, Blacksburg

Abstract

Data collected on 997 bulls which had completed either a 140-day ROP test at Culpeper, Virginia, or a 168-day ROP test at Front Royal, Virginia, were subjected to least squares analysis of variance to determine the effects of several factors on four performance traits. The performance traits studied were lifetime ADG, ROP test ADG, 365-day weight and end-of-test type score.

Breed of bull had a significant effect on lifetime ADG, ROP test ADG and 365-day weight, with the Shorthorns and Herefords generally excelling in all three traits. There were no significant differences due to breed in end-of-test type score. Breed effects were significant on lifetime ADG, 365-day weight and end-of-test type score in the analyses of individually-fed Front Royal bulls and 365-day weight of the group-fed Front Royal bulls. Significant year differences were found in 365-day weight in all analyses. The masculinity development of the bull significantly influenced his end-of-test type score but not his gains or 365-day weight. Dwarfism status of the bulls significantly influenced lifetime ADG and ROP test ADG of the individually-fed bulls tested from 1955 to 1960, but the effects were not entirely consistent with results of other work.

Age of dam significantly affected 365-day weight of bulls tested at Culpeper, with a similar trend in lifetime ADG. In the Culpeper tests, bulls from older cows gained faster and weighed more at 365-days of age. Age of dam had no significant effect on any of the traits of the Front Royal bulls. Preweaning type score significantly influenced end-of-test type score in all analyses and all traits in the analysis of individually-fed Front Royal bulls. As preweaning type score increased end-of-test type score increased and rate of gain and 365-day weight decreased. As age at the beginning of test increased, end-of-test type score and ROP test ADG increased, lifetime ADG remained unchanged and 365-day weight decreased.

An increased pretest ADG caused an increased lifetime ADG and 365-day weight, as would be expected since these are part-whole relationships. The relationship between pretest ADG and ROP test ADG was positive but not significant.

¹ Published with the approval of the Director of Agriculture and Home Economics Research.

² Part of a thesis submitted by the senior author in partial fulfillment of the requirements for the Master of Science degree at Virginia Polytechnic Institute, Blacksburg, Virginia.