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Length of Feeding Period and Number of Animals Required to Measure Economy of Gain in Progeny Tests of Beef Bulls¹

U. S. Department of Agriculture and Montana, Agricultural Experiment Station

Abstract

Data on 62 individually fed steers were analyzed to obtain information on the length of feeding period required to measure efficiency of feed utilization and on the number of steers upon which records should be obtained to adequately test a bull's transmitting ability.

A feeding period of 168 days was found to be sufficient to indicate differences between progeny groups, provided the data were adjusted for differences in initial weight. This finding was based on an analysis of variance and covariance. If the method of least squares were used to determine the regression of mean weight with efficiency, at least 5 or 6 twenty-eight-day periods would be necessary to determine the slope of the regression.

Carcass grade would be affected by the use of a shorter feeding period. Approximately 80 per cent of the differences in carcass grade could be accounted for by differences in initial weight and total gain while on feed. An increase of slightly over one market grade would be expected for each 100 pounds increase in initial weight, and 2/3 of a grade for each 100 pounds increase in total gain.

The number of individually fed steers necessary to give a reasonably good test of a bull's ability to transmit efficiency of feed utilization is approximately 8. Beyond this number little additional information is gained per steer added.

¹ Based on work conducted cooperatively by the U. S. Department of Agriculture and the Montana Agricultural Experiment Station.

² Bureau of Animal Industry, Beltsville, Md.

³ Montana Agricultural Experiment Station, Bozeman, Montana.

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