U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska


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Published in Beef Research Program Progress Report (1985) No. 2: 5


Rapid growth is an important trait for market beef production. Faster growth rate increases the proportion of feed intake that is used for building body tissues and reduces total input/unit of weight gain. This happens because over one-half of the feed energy and nearly two-thirds of the total cost for growing the beef animal goes to maintain normal life processes.

Selection for increased growth rate has been directed largely at postweaning gain because it is highly heritable. Performance tests to evaluate postweaning gain generally vary in length from 112 to 252 days with initial dates beginning at weaning or 30 to 60 days after weaning. The optimum length is determined by the heritability of gains, by cost, and by availability of records early enough to make selection decisions before the first breeding season. Heritability is the fraction of the observed differences between animals caused by average genetic effects, and selection accuracy increases as heritability increases.

A study was made to determine whether the interval length for postweaning adjustment and gain evaluation influenced the heritabilities and genetic correlations of gains evaluated for different time periods.