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Evaluating Relationships among Immature Measures of Size, Shape and Performance of Beef Bulls. II. The Relationships between Immature Measures of Size, Shape and Feedlot Traits in Young Beef Bulls^{1, 2,}

University of Arkansas, Fayetteville 72701 and U.S. Department of Agriculture, Knoxville, Tennessee

Abstract

The correlations of overall size, shape and ten body measurements at 4 and 8 months to feedlot performance were obtained for 550 Hereford (H) and Angus (A) bulls. Size and shape description were obtained from principal components analyses of the ten body measures for each breed at each age. The correlations indicated that, generally, an increase in any one body dimension was associated to some degree with increased gain, weight and feed consumption in both breed groups. Increases in body dimensions had different effects on feed conversion of the two breed groups. Increasing the dimensions of H bulls improved feed conversion but increasing any one dimension of A bulls had an adverse effect on feed conversion. The first principal component which combined all body measures including weight into a single linear index contrasted large framed bulls with small framed bulls. The conclusions from the correlations between overall size and feedlot performance were similar to those drawn from single measurements.

Three concepts emerged from the correlation analyses of shape and performance. Immature body shapes were associated with subsequent performance on test and more than one shape showed positive relationships to efficiency and rate of gain on test. Bulls which months subsequently grew well on test. Tall were larger in all measurements at 4 and 8 and narrow bulls of both breed groups at 4 and 8 months were observed to eat more feed, weigh more at the end of test and gain more but less efficiently than short, wide bulls. The correlations between shape and performance indicate that correlations between single measures and performance traits should be qualified. Logically, the effect of one body dimension on performance of a bull depends upon its relationship to other body dimensions. The data support the hypothesis that shape may be the result of developmental homeostatic mechanisms attempting to compensate for extremes in any one dimension. Several immature shapes were identified which had acceptable performance on test. With a variety of body shapes showing acceptable feedlot performance, the problem concerning the breeder becomes one of identifying those body types which are consistent with efficiency in other phases of beef production.

¹ Published with the approval of the Director of the Arkansas Agricultural Experiment Station.

² This study supported in part by a grant from Agricultural Research Service, U.S. Department of Agriculture.

³ Department of Animal Sciences, University of Arkansas, Fayetteville.

⁴ Animal Science Research Division, A.R.S., University of Tennessee, Knoxville.