Double trouble: Implications and management of twinning in lactating dairy cows

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Over the past 4 decades, twinning increased concurrently with milk production in dairy cattle, but recently appears to have plateaued, likely from the adoption of hormonal synchroniza­tion protocols. Approximately 95% of Holstein twins are dizy­gotic, making double ovulations the primary mechanism for twinning. Decreased progesterone (P4) concentrations dur­ing preovulatory follicle growth increases double ovulations. Increased hepatic catabolism of P4 because of increased feed intake associated with increased milk production provides a physiological mechanism for decreased P4 concentrations and increased double ovulations. Cows with unilateral twins have more pregnancy losses than cows with bilateral twins which were similar to cows with singletons. Selective embryo reduction followed by P4 treatment did not increase the risk of pregnancy loss for cows with unilateral twins, but increased the risk of loss for cows with bilateral twins. Twinning will likely increase concurrently with milk production over time but can be decreased using 2 approaches: 1) submitting cows to hormonal synchronization protocols that increase P4 dur­ing growth of the preovulatory follicle before timed AI; and 2) identifying twins by laterality and allowing cows with bilateral twins to continue through gestation with extra assistance at calving, while selective reduction can be attempted for cows with unilateral twins.