An estimation of genetic progress in the Angus herd at Ames Plantation

The performance records of 3,144 non-creep fed, purebred heifer and bull calves born at Ames Plantation were utilized in the study. These data were collected over an 18-year period (1957-1974), being divided into two groups, (1957-1966) and (1967-1974). Average daily gain, weaning type score and weaning weight were the factors studied in these analyses. The objectives of this study were to take data from the Ames herd and calculate estimates of the genetic trends within the herd. Also, the influence of age of dam, sex of calf, and season of birth on average daily gain from birth to weaning was evaluated. An analysis was performed for each group for average daily gain, weaning type and weaning weight. Sex of calf had a highly significant effect (P < .001) on aver-age daily gain for both groups. In these analyses, male calves gained 0.17 and 0.18 pound per day greater than their female counterparts. Sex of calf effects on weaning weight were also highly significant (P < .001) with male calves having a weight difference of 44 and 42 pounds greater for the two groups, respectively. Although sex effects on type score were not significant for the first group, the difference for the second group was significant with the female calves outscoring the male calves by 0.13 of a unit. The effects of age of dam on gain from birth to weaning were highly significant for both groups. These data show that a cow's individual performance was lowest at 2, 3, 4 and 12 years of age. Estimates of age of dam effects on type score indicate that the maximum type score of a cow's calves was obtained within the age range of three to nine years. Season of birth had a highly significant (P < .001) influence on average daily gain from birth to weaning for both groups. Calves born in Season II grew faster than did calves born in Season I and IV. While season of birth had a significant effect (P < .01) on type score at weaning in both groups, but the effects were not consistent. Heritability estimates of average daily gain from birth to weaning were 0.33 to 0.32 for groups I and II, respectively, while heritability estimates of type score at weaning were 0.41 and 0.36 for the data groups I and II. Genetic correlations of average daily gain and weaning type were 0.56 and 0.37 for group I and II, while the phenotypic correlation of these traits was 0.41 for both groups. Estimates of genetic progress were 0.0078 and 0.0343 pound increase in average daily gain per year for data groups I and II, respectively. These estimations, in terms of progress per generations, would be 0.036 and 0.172 pound increase in average daily gain. A second analysis was done eliminating season from the model, using only data from Season I. This gave estimations of 0.036 and 0.027 pound increase in average daily gain per year and 0.179 and 0.137 pound progress per generation.