Contribution of non-genetic factors to the reproductive performance of Mirandesa cows.

Characterization of reproductive traits in Mirandesa beef cattle is important for breed improvement and conservation, mainly due to its little genetic diversity. Reduced individual and maternal performance is often associated with inbreeding depression, which could be further aggravate the environmental effects. In this study, 7386 herd records for Mirandesa were used to characterize the main reproductive traits, like age at first calving (AFC), pregnancy length (PL), calving interval (CI), yearly calving distribution (CD) and productive lifespan (PLf). The non-genetic effects were tested using non-parametric methods, as the target variables were not normally distributed. The median for AFC in Mirandesa was close to 32 months; AFC was affected by the production system, farm and by the year and season of birth. The mean for PL was 287±8.9 days, being affected by parity and calf gender. The median CI, of 378 days, was only affected by the breeding program, parity, season and year. Calving season was unevenly distributed over the year, showing different patterns after the production system. The mean productive lifespan of Mirandesa was 6.45 years, though 20% of the cows presented a PLf longer than ten years. The main non-genetic effects suggested that farmer's decision and nutrition may constrain the expression of the reproductive traits in Mirandesa breed. This aspect needs to be addressed when designing any breeding programs which should prioritise for the increase in the number of calves per year along with a careful selection of reproducers to decrease reported inbreeding. [ABSTRACT FROM AUTHOR]