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

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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 of 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 weeks or at 0.75 times maintenance for 6 weeks and at 1.25 for 6 weeks. Changes in body weight of each cow were estimated from regression lines fitted to weekly weights. Height at the hoods was recorded in centimeters and condition was estimated by ultrasonic measurement or a visual score. When fed at 1.0 times maintenance there was little average gain or loss of body weight 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 body weight gain or loss between rations or breeds. In 1 experiment there was greater variation in weight change within 2 observations on the same cow than that obtained between cows. Cows with a high weight-height ratio tended 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 2 separate experiments. 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 - kcal DEm = 130W0.75 - (W/H - 4.0) 1716.

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