Abstract
Reproductive data (1973-87) from seven breed groups, at the Debre-Zeit Agricultural Rsearch Centre dairy herd (Ethiopia), were analysed. Both breed and environmental effects, including period (years grouped), season, parity, and sex of calf, were quantified. Conception patterns were seasonal and correlated with mean monthly maximum temperature (r = 0.62). The mean interval between detected oestrous cycles was long (71 days). About 26% of all the intervals was between 6 and 32 days; double cycle, with one silent or missed heat in between, constituted 23.4% of the intervals. The rest, which ranged between 52 and 320 days, comprised close to 50% of all the intervals. Number of services per conception, which varied from 1.11 Barca (Ba) to 1.63 grade Friesians (GF), was influenced by breed and season of conception. Gestation length ranged from 272 [3/4 Friesian - 1/4 Boran (FFBo) crosses] to 280 days (Ba) and was only affected by parity. Age at first calving varied from 34.0 [F1 Friesian-Barca (FBa)] to 38.2 months [F1 Friesian-Boran (FBo) crosses]. Abortion rate was high among Ba (9.3%) and Friesian (F) (8.4%) breed groups. Breed of cow and period of calving affected calving interval; this varied from 388 (FBa crosses) to 471 day [3/4 Friesian - 1/4 Barca crosses (FFBa)]. Similar trends were noted for days open. Generally, reproductive performance of the overall herd declined over the years. Barca and F1 crosses manifested better reproductive performance than the rest.
