An evaluation of mature size in beef cattle and its relationship to production efficiency

Abstract

Forty-nine Hereford cows and 27 Charolais cows, aged 5 to 9 years, were maintained in drylot from one to five years at the Texas A&M University Agricultural Research Center at McGregor. Biweekly weights, individual feed consumption, and monthly estimated milk yields were recorded. Cows were fed to maintain a constant, uniform fleshing condition as determined by visual appraisal. Calves were individually fed and weighed monthly until weaning and biweekly thereafter. Cows and calves received a feed mixture of 10% cottonseed meal, 10% oats, 30% grain sorghum, and 50% sorghum hay, with 64% TDN content. Bull calves were castrated at weaning. Claves were weaned at 210 days of age, placed in feedlot, and fed until slaughter. Chest depth (CD), hook width (HW), and body length (BL) were measured on 71 cows. Mature body weight (AW) was measured as the average of biweekly weights taken between successive parturitions. Cows which failed to calve were removed from the test. Principal components were computed for each of the four correlation metrics, composed of the correlations between the three linear body measurements and average weight. The four matrices included one for each year separately and pooled, within-year matrix. Repeatability across years was 0.85 for the first principal component and 0.00 for the second. The component associated with the largest root of the pooled, within-year matrix accounted for 75% of the generalized variance and was interpreted as a general size factor. The second component was primarily a contrast between HW and BL and appeared to distinguish between endomorphic and ectomorphic cattle. The first two components accounted for 90% of the generalized variance. The correlation of average cow weight with the first principal component was 0.93 and suggested that average weight was a good indication of mature cow size. Correlations of the first two components with calf performance traits indicated that calves from larger mature cows tended to grow more slowly than calves from smaller mature cows. ...