Twinning in Italian Holstein Cows: A Retrospective Study on Risk Factors and Its Associations with Milk Production, Fertility, and Survival.

Twinning in cattle is an increasingly common reproductive phenomenon that has significant implications for herd productivity and animal welfare. This retrospective study aimed to assess the occurrence rate of twinning (TW) in Italian Holstein multiparous cows and to identify the associated risk factors and consequences with respect to fertility, milk production, and cow survival. Data from 44,535 calvings across 61 Italian dairy farms from January 2019 to December 2020 were analyzed. The overall TW rate was found to be 3.79%, affected by factors such as parity ( < 0.0001), season of conception ( < 0.0001), previous lactation 305-day mature equivalent ( < 0.05), and prior days open ( < 0.0001). Cows experiencing TW had significantly shorter gestation lengths ( < 0.0001) compared to singletons and lower 305-day milk production estimates (11,094 kg for TW vs. 11,295 kg for singleton females and 11,318 kg for singleton males) ( < 0.0001). Moreover, TW was linked to a decreased pregnancy risk and an increased risk of culling ( < 0.0001) both in short- and long-term analysis. These findings underline the need for targeted management strategies to mitigate the adverse effects of twinning in dairy herds, especially where TW rates are notably high.