FACTORS AFFECTING THE REPRODUCTIVE-PERFORMANCE OF BORAN (BOS-INDICUS)COWS IN A SINGLE-SIRE MATING SYSTEM

A total of 179 heifers, primiparous and multiparous Boran cows were as signed to four breeding units and mated over a 4-month breeding season in a single-sire mating system. Mean body weight and body condition s cores at the beginning of mating ranged from 363 +/- 6 kg to 388 +/- 7 kg and from 6.7 +/- 0.1 to 7.0 +/- 0.1 in the four breeding units, re spectively. Body weight losses in cows in the four breeding units rang ed from 8 to 35 kg over the mating period, losses being higher in lact ating cows (44 kg) than in non-lactating cows (6 kg). Pregnancy rates ranged from 81 to 94% in the four breeding units and were not influenc ed by lactation status. First calf heifers had the lowest pregnancy ra te with a tendency for increasing pregnancy rates with parity in multi parous cows. Lactating cows calved later (P < 0.05) than did non-lacta ting cows, and heifers calved later (P < 0.05) than cows. A smaller pe rcentage of heifers (43%) than multiparous cows (64%) calved during th e first two calving months. There was no significant correlation betwe en body weight, weight changes or calf growth performances, and pregna ncy rate and calving patterns.