An estimation of genetic progress in Tennessee beef cattle

The data used in this study were from the Tennessee Beef Cattle Improvement Program weaning records from 27,008 Hereford, Polled Hereford, and Angus calves accumulated over an 18 year period, 1961 through 1979. The calves were classified according to weaning age (within the range of 160 to 250 days inclusive); sex (bulls, heifers, and steers); age of dam (by years from 2 to 5 inclusive; 6 which included all 6 to 10 year olds, and 11 years and over; month of birth; management (creep or non-creep fed); year and breed in the preliminary analysis. The calves were divided into six sub-groups according to breed and management. The purposes of this study were to estimate weaning weight adjustment factors, heritabilities, and genetic trends of each of the sub-groups.

An analysis of variance was performed for each group for weaning weight. Sex of calf had a highly significant effect (P < .01) in all groups with the bull calves weaning heavier than the steers and the steers heavier than the heifers.

The effect of age of dam on weaning weight was highly significant for all groups. In the non-creep groups the 6, 7, 8, 9 and 10-year-old cows weaned the heaviest calves, while in the creep-fed groups the heavier calves were weaned by the 11-year-old and over cows.

Season of birth had a highly significant (P < .01) influence on weaning weight with the sub-group falling into two categories. The Hereford non-creep. Polled Hereford creep, and Polled Hereford non-creep fed calves weaned heavier when born in December, January, or February while the other three groups weaned heavier calves that were born in March, April, and May.

Least squares constants were calculated for age of dam, sex of calf, and season of birth for each breed-management group and these constants were then used to adjust the weaning weights.

Heritability estimates of weaning weight were .70, .63, .72, .08, .36, and .21 for Hereford non-creep, Hereford creep, Angus non- creep, Angus creep. Polled Hereford non-creep, and Polled Hereford creep, respectively.

Estimates of genetic progress were .08 and -.20 pound increase per year for Hereford non-creep and creep fed calves, respectively. Angus non-creep fed calves showed a genetic progress of -.05 pound increase per year while the Angus creep fed calves had a -.11 pound per year increase. ThePolled Hereford genetic progress was.10 and -.41 pounds per year for non-creep and creep fed calves, respectively.