Date of Award
Master of Science
R.R. Shrode, D.O. Richardson, S.L. Hansard
Data on 1,192 calves from 382 Angus and Hereford cows in six University of Tennessee beef herds were used to study the relationship between pre-weaning performance of females and their subsequent producing ability as measured by pre—weaning performance of their calves. Least-squares constants were fitted for the independent variables, herd, year of birth of the dam (YOD), adjusted average daily gain of the dam from birth to weaning (AADG(D)), age of dam (AD), type score of the dam at weaning (TS(D)) and condition score of the dam at weaning (CS(D)) in order to determine their effects on the dependent variables, average daily gain of the calf from birth to weaning (ADG(C)), adjusted average daily gain of the calf from birth to weaning (AADG(C)), weaning weight of the calf (WW(C)), type score of the calf (TS(C)), condition score of the calf (CS(C)) and most probable producing ability (MPPA). MPPA values were calculated for individual cows in the Plateau Experiment Station herd (PES) and the Ames Plantation herd (AP).
Generally, pre-weaning performance was lowest for calves of 2-year~old cows, and the greatest difference in pre-weaning performance was observed between calves of 2- and 3-year-old cows. The significant positive correlations between AADG(C) and CS(C) in the 2-year-old AD group reflected the lower maternal ability of some younger cows and its effect on subsequent rate of gain of the calf. In addition, the correlation between CS(C) and TS(C) was lower in mature cows than in younger cows.
Phenotypic correlations suggested that TS(D) and CS(D) were the only pre-weaning performance traits of the dam which exerted a negative influence on calf pre-weaning performance traits. However, these antagonisms between dam and calf traits do not necessarily appear in the earliest AD groups. No obvious trends were evident with respect to the effect of CS(D) on calf rate of gain.
The herd in which the calf was raised accounted for more variation in calf performance than any other single variable and this effect tended to increase as AD increased. YOD, generally, exerted a greater influence on TS(C) and CS(C) than on rate of gain and also was higher in the 2nd, 3rd or 4th lactation.
High positive phenotypic correlations between type score and condition score were observed. This fact and the trend toward increased influence of TS(D) on rate of gain of the calf, when CS(D) was not considered, suggests that, to a degree, these were measures of the same trait.
Pre-weaning growth rate of the dam appeared to have little effect on TS(C) or CS(C), but, especially in the AP herd, AADG(D) had a significant effect on ADG(C) and WW(C). Coefficients of correlation between the dam's weaning traits and MPPA value for AADG(C) indicated that pre-weaning environmental conditions which favored high CS(D) had a detrimental effect on subsequent calf performance. The significant effect of CS(D) and AADG(D) on MPPA further strengthens the hypothesis that overly conditioned (fat) heifers subsequently produce calves which gain more slowly while the more rapidly gaining heifers, that are not fat, subsequently produce calves which gain more rapidly.
These results indicate that some method of adjusting weaning records for variation in condition would increase the effectiveness of selection for AADG. Phenotypic relationships in this study suggest that an appropriate method of managing replacement heifers may be to sort them from other calves in the herd prior to weaning and provide nutritional environment which will result in rapid gain without significant fattening.
Warren, James Howard, "The relationship of pre-weaning performance with subsequent producing ability in beef cows. " Master's Thesis, University of Tennessee, 1973.