Genetic and Non-Genetic factors affecting age at first calving of N’Dama Heifers
A total of 1756 N’Dama heifers born on the farm over a period of 29 years (1949 – 1977) were studied, to investigate the effects of their year of birth (BTHYY), season of birth (BTHSN), inbreeding of its calf (CALINB) and inbreeding of the heifer (DAMINB) on their age at first calving (AFC). BTHYY and DAMINB were highly significant (P<0.01) on AFC, BTHSN was significant (P<0.05) while CALINB was not significant (P>0.05) on AFC. AFC in the heifers studied (N=1756) ranged from 26 – 56 months, with a mean AFC of 40.43 ± 0.18 months with a CV of 18.95 percent. Heifers born in 1955 (n=152) had the least AFC (35.51 ± 0.54 months) while those born in 1968 (n=5) had the highest AFC (51.54 ± 2.94 months). Heifers born during the early dry season had the least AFC, while those born during the late dry season had the highest AFC. The mean CALINB and DAMINB in this study were 1.18 percent and 0.29 percent respectively. There was a correlation of 0.06 between both factors. DAMINB had a significant (P<0.01) influence on AFC with a percentage increase in DAMINB resulting in 0.3315 months (about 10 days) increase in AFC of heifers.
Keywords: Age at First calving, Beef Cattle, Heifers, Inbreeding, N’Dama and Reproductive ability