Some factors affecting performance in three closed lines of Hereford cattle

The influence of years, lines, age of dam, years x lines, inbreeding of dam, inbreeding of calf, and weaning age, on performance traits in three closed lines of Hereford cattle was studied.Data were collected over a 14-year period at the North Montana Branch Experiment Station.Records from dams of three closed lines and their subsequent calf production were included in a least squares analysis.Heifer and bull calves were analyzed separately.Weaning weight and final feed-test weight were corrected for the age of the calf.Analysis of variance was performed to indicate the effects on birth weight, 180-day corrected weaning weight, final feed test weight, and average daily gain on test.Years had a highly significant effect on all traits studied.Lines produced a significant effect on birth weight in heifer and bull calves and 180-day corrected weaning weight in the heifer calves.Age of dam showed a depressing effect on weaning weight from younger cows, but the reverse was evident in postweaning gain, which indicated a compensatory effect in the postweaning environment for the preweaning environment.Years x lines was used as the only estimate of sire effect in these one sire lines, realizing this estimate was confounded.This effect was most evident in the postweaning daily gains in both heifer and bull calves.Inbreeding of dam indicated a positive effect on birth weight, but a negative effect on weaning weight.Bull calves were depressed significantly by inbreeding of dam.This depression may be due to the bulls having a greater growth potential, retarding them more than the heifers by the decreased milk supply.Inbreeding of calf did not have any significant influence on productive traits studied, but partial regressions of weight on inbreeding of calf were negative.Regressions of weight on weaning age indicated heifer calves born early in the calving season are retarded in their preweaning gains when compared to those born later in the calving season.This was not the case with the bull calves.Mature weight was affected by inbreeding of the dam when the weight was taken after a period of stress such as calving and early lactation period.Maturity of the dams was estimated to be reached at six years of age in the three inbred lines studied.