Efficiency of Production and Cow Size in Beef Cattle

Abstract

Data from 56 identical and fraternal twin beef cows collected during the interval of 240 days to 5 yr. of age were used to calculate several measures of efficiency of production. The relationships of the efficiency estimates with cow size and other traits of the cow and calf were studied. The associations were calculated to represent the expected values for unrelated single born animals on the assumption that any physiological differences between twin and non-twin cattle do not alter the relationships between the traits considered. The estimates of efficiency were: negatively related to cow weight at calving; positively, but seldom significantly, associated with cow height at withers; and negatively related to the ratio of weight to height at withers, an indicator of degree of fatness. These relationships lead to the hypotheses that fatter cows are less efficient producers of calves and that skeletally large and small cows are approximately equal in efficiency, with a possible advantage for the large cow. Age at calving or reproductive performance appeared to be the most important single variable for predicting differences in the estimates of efficiency of production. Few of the correlations of efficiency of production with early traits of the cow were large. Efficiency of weight gain from 240 days to 15 months was positively correlated with efficiency of production. This was the only relationship which suggested that indirect selection for efficiency of production at an early age may be possible. The economics of using large or small cows as brood stock is discussed with regard to fixed costs per cow, the relative merits of the progeny and measures of reproductive performance. The conclusion reached in all instances is that large cows tend to be more profitable.