Inbreeding depression in Holstein cattle in Brazil

Abstract

The objective of this study was to evaluate inbreeding depression in Holstein cows in Brazil, considering their 305-day milk production (MP), age of first calving (AFC), and calving interval (CI). The effects of inbreeding depression on the traits were determined using four regression models (linear, quadratic, exponential, and Michaelis-Menten) about the errors generated by the animal model. The linear model was significant for CI, and the quadratic model was significant for CI and AFC. The Michaelis-Menten and exponential models were significant for MP, AFC, and CI. Inbreeding depression affected MP and CI. Cows with inbreeding coefficient of 15% produced approximately 260 kg less milk than non-inbred cows. A 1% increase in the inbreeding level resulted in an unfavorable increase of CI of 1.88 days. The quadratic and exponential models showed no variations for CI with increasing inbreeding level; however, the Michaelis-Menten model showed a positive effect of inbreeding on CI. Despite of the small number of inbred Holstein cows, the inbreeding negatively affected milk production and calving intervals. Therefore, breeders should monitor their cattle inbreeding levels. The Michaelis-Menten and exponential non-linear models are best suited to fit inbreeding data of Holstein cows