A study on the reproduction of local Zebu and F1 Crossbred (European X Zebu) cows II. Age at first calving and calf production.

Data on 655 Ethiopian zebu and first generation (Fi) cross-bred cows were analysed by least squares procedures to study the effect of crossbreeding and other factors on age at first calving, calving interval and calving rate measured as number of calves born per cow per year since first conception on the station. There were three sire breeds, Friesian, Jersey and Simmental; three Ethiopian zebu dam breeds, Barka, Boran and Horro, at four stations, Baf. and Holetta as set I and Adami Tulu and Melka Werer as' set 2. Estimates of the means of age at first calving for crossbred cows were 35.5 mo in set 1 and 40.3 in set 2. Means of calving interval were estimated as 507 days for local cows in set 1,484 for locals in set and 422 for crossbreds in set 1. There were not enough records to estimate calving intervals for crossbreds in set 2. Calving rate was estimated as .37, .33, .66 and .60 calf per cow per year since first conception on the station for local cows in set 1 and 2 and crossbred cows in the two sets, respectively. Most of the factors considered, except station and the selected first order interactions between some of them, did not show any significant effect in most of the analyses. Sire breed was only significant in age at first calving in crossbred cows of set 2. Particularly absent were effects of interaction of sire breed x station and dam breed x station which may indicate that there was no particular breed, sire or dam, which performed particularly differently in a specific station. However, firm conclusions should await analysis of a larger body of data. Catle in Ethiopia, numbering approximately 26 million, represent the most important sector of the livestock. However, studies showed that productivity of the local cattle is low. Yearly milk yield per cow under above average conditions was estimated to range between 0 and 1528 kg with a mean close to 570 (8). In an effort to improve the productivity of local animals the Ethiopian Institute of Agricultural Research (IAR) has initiated a programme to cross native cattle breeds with European ones. This series of papers deals with effect of crossbreeding on the reproductive performance. The first paper of the series (2) dealt with number of services per conception, days open till conception and gestation length. The aim of the present paper is to investigate the effect of crossbreeding and other factors on age at first calving and efficiency of calf production.