Abstract
A total of 1 79 heifers, primiparous and multiparous Boran cows were assigned to four breed units and mated over a 4-month breeding season in a single-sire mating system. Mean body weight and body condition scores at the beginning of mating ranged from 363 ± 6 kg to 388 ± 7 and from 6.7 ± 0.1 to 7.0 ± 0.1 in the four breeding units, respectively. Body weight losses cows in the four breeding units ranged from 8 to 35 kg over the mating period, losses being high in lactating cows (44 kg) than in non-lactating cows (6 kg). Pregnancy rates ranged from 81 94% in the four breeding units and were not influenced by lactation status. First calf heifers I the lowest pregnancy rate with a tendency for increasing pregnancy rates with parity in multipan cows. Lactating cows calved later (P < 0.05) than did non-lactating cows, and heifers calved 12 (P < 0.05) than cows. A smaller percentage of heifers (43%) than multiparous cows (64%) calves, during the first two calving months. There was no significant correlation between body weight, weight changes or calf growth performances, and pregnancy rate and calving patterns.
