| Pregnancy rate (PR), calf crop born (CCB), cow weight at palpation (WT) and cow body condition score (CS) were analyzed for Angus (A), Hereford (H) and Brahman (B) straightbred cows, F1 and F2 B-A and B-H cows, and ⅜ B ⅝ A first (Bn1) and second generation (Bn2) cows in Central Texas. Heterosis was estimated by linear contrasts within breed group-age category (two and three year olds in analyses of B-A and two, three and four year olds in analyses of B-H). In analyses of B-A crossbreds and straightbreds, F1s expressed significant heterosis for PR (.35), CCB (.14) and CS (.13) as two year olds, and for WT as two and three year olds (28.2 and 20.7 kg). F2s expressed significant PR heterosis (.48); greater than that of F1s as two year olds. F2s expressed significant heterosis for WT as three year olds (39.1 kg), but expressed significant negative heterosis for CS (--.45) as two year olds. In analyses of B and H straightbreds and crossbreds, F1s expressed significant heterosis for PR as two year olds (.26), and for WT as two, three and four year olds (greater than 43.0 kg). F2 BH cows expressed significant heterosis for WT as three year olds (31.8 kg); they expressed significant heterosis for PR (.27) as two year olds. F 2 four year old cows expressed negative heterosis for CS (--.66). The later age at puberty of B, the age of the dams of these cows when these cows were born and raised, and prior year performance of cows were important factors that influenced these results. Genetic effects were also estimated using multiple partial regression techniques. Additive effects (B as deviations from A or H) were negative for PR and CCB and positive for WT and CS. In analyses of B and H, maternal effects (for B as deviation from H) were significant for CCB, and maternal heterosis was negative for WT and CS. Direct heterosis was positive for all traits in analyses of B and H and for PR and WT in analyses of B and A. |
