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Effect of Cow Size and Condition and Ration Protein Content upon Maintenance Requirements of Mature Beef Cows¹

Ohio Agricultural Research and Development Center, Wooster

Abstract

Sixty-two mature, non-pregnant, non-lactating Hereford and Charolais cows were used to study the effect of cow size and condition and protein content of the ration upon energy requirements for maintenance. Complete pelleted rations which contained 6.9, 9.1 or 12.0% total crude protein were individually fed once daily to cows in dry lot which were bedded with sawdust. Each ration was fed to supply digestible energy at theoretical maintenance levels for periods of 12 to 16 wk. or at 0.75 times maintenance for 6 wk. and at 1.25 times maintenance for 6 wk. Changes in bodyweight of each cow were estimated from regression lines fitted to weekly weights. Height at the hooks was recorded in centimeters and condition was estimated by ultrasonic measurement or a visual score.

The level of energy as fed appeared adequate for maintenance. When fed at 1.0 times maintenance there was little average gain or loss of bodyweight and the average weight change obtained from feeding at 0.75 and 1.25 times maintenance also approached zero. Least-squares analysis of the data showed no significant differences in bodyweight gain or loss between rations or breeds. In one experiment there was greater variation in weight change within two observations on the same cow than that obtained between cows. However, there was a tendency for cows with a high weight-height ratio to gain more than cows with a low weight-height ratio, as indicated by partial regression coefficients of 0.127 and 0.094 obtained in two separate experiments. Cows that had a high degree of finish tended to gain weight while those that were in a thin condition lost weight when the amount of energy fed was based on their metabolic body size. There was a highly significant correlation between condition and weight-height ratio. An equation which would adjust maintenance requirements to the condition of the cow was estimated to be—

¹ Approved for publication as Journal Article No. 36-67 by the Associate Director of the Ohio Agricultural Research and Development Center, Wooster. This work was a part of the North Central Regional Project, NC-1. Improvement of Beef Cattle Through Breeding Methods.

² Department of Animal Science. A portion of the data presented are from the M.S. Thesis of L. G. Sanford, The Ohio State University, Columbus.

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