Reproduction efficiency of zebu and crossbred cows as measured by the inter-estrus and inter-service intervals at Bako

The study was conducted to evaluate the reproduction efficiency of zebu and crossbred cows measured by the inter-estrus and inter-service intervals using data from Bako Agricultural Research Center. The overall mean inter-estrus and inter-service intervals were 44.3±0.85 and 49.1±1.24 days, respectively. Comparison of the sire breeds indicated that the Jersey crosses had significantly (p0.00) the shortest inter-estrus (43.9±2.57 days) and inter service 41.8±4.01 days) interval compared to the other sire breeds. The Boran and the Horro had the longest inter-estrus (51.2±3.10 days) and inter-service (62.2±2.92 days) intervals, respectively. Neither the crossbred nor the zebu cows significantly differed among each other in both traits. As a dam breed, the Horro was not significantly (p0.05) different from Boran in inter-estrus and inter-service intervals. Cows in the first parity had significantly (p0.001) the longest (55.8±2.61 days), while cows in the sixth parity had the shortest (40.3±2.25 days) inter-estrus interval, while the effect of parity on inter-estrus and inter-service interval was not significant (p0.05). The first inter-service interval was significantly (p0.01) the longest (64.2±3.91 days) compared to subsequent inter-service intervals. The longest (p0.001) inter-service interval was observed in 1997 (68.6±7.32 days) and the shortest was recorded in 1998 (33.5±13.06 days), while the longest enter-estrus was recorded for cows that calved in 1991 (73.9±6.07 days) and the shortest for 1985 (30.4±4.17 days) Distribution of the inter-estrus and inter-service intervals into different estrus cycle length categories indicated that 43.2 and 42% of the inter-estrus and inter-service intervals were within the normal (18 to 24 days) range of estrus cycle, while 13 and 5.6 percent were short (17 days) and 38.8 and 45.4 percent were long (36 days), respectively.