|Van Vleck, Lloyd|
Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 7/1/1999
Publication Date: N/A
Technical Abstract: Survival analysis was used to investigate herd life of 537 females produced in 1973 and 1974 in a four breed diallel design including Red Poll (RP), Brown Swiss (BS), Hereford (H) and Angus (A) breeds. Data were collected at the U.S. Meat Animal Research Center, and included records of cows from 57 sires (15 H, 16 A, 15 RP, and 11 BS). A Weibull regression model was used to explain the effect of the breed combination on herd life measured by th number of days from the beginning of the first breeding season of the cow to her termination from the herd. Model included fixed effects of breed combination, and year of birth of the cow, with sire within breed of sire as a random effect. Significance of the explanatory variables was tested using a likelihood ratio test. The effect of breed combination was significant (P < .05). The change in log likelihood associated with the year of birth was small compared with that of other effects. The estimate for the scale parameter was 0.81 plus/minus 0.04, indicating a baseline hazard function which decreases over time. Solutions for fixed effects indicated a higher probability of being culled for purebred than for cross- bred cows (P < .01). Heterosis was favorable for F1 Angus-Brown Swiss and F1 Hereford-Brown Swiss crosses (P < .01 and P < .05, respectively). The risk ratios for the breed combinations were 1.2, 1.5, 0.8, 0.9, 0.6, 1.6, 0.7, 0.5, 0.9, 0.5, 1.2, 0.9, 0.8, 0.9, 0.7, and 1.0 for RP, RPxBS, RPxH, RpxA, BSxRP, BS, BSxH, BSxA, HxRP, HxBS, H, HxA, AxRP, AxBS, and A, respectively. Brown Swiss crosses were superior to A and H breeds. The significant breed group differences in herd life indicate that purebred cows have a higher risk of leaving the herd than crossbred cows.