THE EFFECT OF AMOUNT OF BODY-FAT AND LOSS OF FAT ON BREEDING SOUNDNESS CLASSIFICATION OF BEEF BULLS

Two hundred and fifty-one Aberdeen Angus, Horned Hereford, Polled Here ford, and Charolais bulls were examined at the time of sale (sale) and again from 10 to 85 days later (test) to determine the effect of amou nt of body fat and Loss of fat on semen quality. Sale and test measure ments included body weight, backfat depth, and scrotal circumference. Breeding soundness evaluations were done at test. For all bulls, over all years, the positive correlations of body weight loss vs. backfat l oss, weight loss vs. scrotal circumference loss, and backfat loss vs. scrotal circumference loss were highly significant. Aberdeen Angus, Ho rned Hereford, Polled Hereford, and Charolais bulls lost weight at a m ean rate of 1.77, 2.19, 1.94, 1.16 kg per day, respectively, in the in terval from sale to test. Bulls classified as unsatisfactory lost sign ificantly more weight than satisfactory bulls. However, bulls classifi ed as unsatisfactory did not differ significantly from satisfactory bu lls in the amount of backfat at sale and test and in the amount of bac kfat lost. No significant relationship could be demonstrated between i ncrements of backfat and classifications of breeding soundness evaluat ions. Bulls with satisfactory semen quality had significantly larger s crotal circumference measurements than those with questionable or unsa tisfactory classifications. Backfat data at bull sales may be helpful in selecting bulls with desirable growth characteristics, as well as r educing the risk of purchasing bulls with poor semen quality due to ex cessive body fat.