Effects of parity and previous parous status on reproductive and productive performance of Kenya Boran cows
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A total of 16 220 calving intervals (CI), calving rates (CR), and 12 532 weaning weight records of Kenya Boran cows and calves from five ranches, distributed in three different ecological zones were analysed to estimate effects of parity, previous parous status (PPS), and sex of calf on reproductive and productive traits. Reproductive traits were CI and CR, while productive traits comprised 270-day weaning weight (calf 270) and two different productivity indices: cow index I and cow index II. The data were analysed by the least squares method using a fixed model. Parity significantly affected CI and CR (P < 0.01) and 270-day adjusted weaning weight and the four indices (P < 0.01). Previous parous status affected only calf 270 (P < 0.05) and sex of calf only affected cow index I (P < 0.001). Differences in magnitudes of the effects between ranches were observed. Mean CI estimates ranged from 434 ± 6.1 days for first parity cows to 426.8 ± 8.0 days for cows in their 4th parity, while cows in the 7th parity and above averaged 421.5 ± 15.5 days. Cows that did not calve in the previous parity had mean CI of 422.2 ± 11.4 days while those that had weaned calves, aborted, or had still-births had mean CI estimates of 425.7 ± 2.9, 412.7 ± 14.9, and 423.6 ± 9.8 days, respectively. Calving rates ranged from 82.7 to 91.9% for 1st and 6th parity cows, respectively, with cows in their 7th parity and over, recording 89.4% for this trait. The results suggest the need to adjust for parity, previous parous status, and sex of calf when evaluating cows for reproductive and productive performance.