Factors affecting weight at first service of Holstein Friesian heifers born and reared in a tropical environment

الملخص

The introduction of Holstein Friesian to an environment out of their thermo-comfort zone and to diseases not existing in their original temperate climates, was assumed to affect their reproductive and productive performance. From this assumption came the need to investigate and evaluate the performance of this breed in the hot climate of Northern Sudan, hence the objective of this study. The trait studied was weight at first service under the factors of year and season of birth of heifer, weaning weight class, weaning age class and their interactions. The method of data analysis was the Least Mean Squares. The data were subjected to analysis of variance using the SPSS program version 12.5. A total number of 588 records covering the period from the year 1989 to the year 2002 were retrospectively collected and analyzed. The results showed that the overall mean weight at first service was 337.25 ± 2.76 kg. The effect of the year of birth of heifers on this trait was highly significant (P≤ 0.001). The season of birth of the heifers, age at weaning and weight at weaning exerted no significant effects on the weight of heifers at first service (p ≥ 0.05). The interactions of these factors also showed no significant effect on the trait (p≥ 0.05). The weight at first service revealed by this study was not far from the breed norms in their countries of origin. We can conclude that the Holstein Friesian heifers born and reared under the prevailing environmental and management conditions at the farm of study were able to adapt and perform satisfactorily.