Genetic and nongenetic variation of multiple births in Austrian dual-purpose cows

In recent decades, a general increase in multiple birth (MB) rate has been reported in both dairy and dual-purpose cattle breeds. As there is evidence that MB has negative effects on economically important traits in dairy cows, the aims of this study were to (i) investigate environmental and genetic factors affecting MB rate and (ii) assess the impact of MB on productive and nonproductive traits of the Austrian dual-purpose breeds Pinzgauer and Tyrol Grey. The dataset included 99,141 calvings of 33,791 Pinzgauer and 68,454 calvings of 19,244 Tyrol Grey cows recorded from 2000 to 2022. Environmental factors affecting MB were investigated using logistic regression, and genetic parameters of MB were estimated using linear and threshold animal models. In addition, the effects of MB on milk, fat, and protein yields and calving ease were analyzed using a linear mixed model, whereas stillbirth and cow survival (binary traits) were analyzed by logistic regression. The average MB rate from 2000 to 2022 was 5.80% for Pinzgauer and 3.89% for Tyrol Grey. The lowest MB rate was observed in primiparous cows in both breeds, and the highest in fourth-parity Pinzgauer and seventh-parity Tyrol Grey cows. The highest MB rate was in summer regardless of the breed. In Pinzgauer, the MB negatively affected dairy traits and survival, and in Tyrol Grey, it affected fat yield and calving ease. Stillbirth was notably higher when MB occurred than in single births in both breeds. In Pinzgauer, the estimated heritability was 0.029 (linear) and 0.138 (threshold), whereas in Tyrol Grey, it was 0.040 (linear) and 0.200 (threshold). Low additive genetic variation exists for this trait, but it is still exploitable in genetic programs aimed at curbing the MB rate.