Evaluation of seasonal impact on twinning in Holstein-Friesian dairy herds

Background: Twin pregnancy and twinning in dairy cattle herds reduce the overall profitability. Cows calving twins are at greater risk for periparturient problems as well as metabolic disorders in connection with their reproductive performance. Twin pregnancy increases not only the average days open and services per conception (effect on the dam), but increases the incidence of abortion, stillbirth, mortality and foetal growth retardation in the twin calves. Some factors (e.g. parity, season, genetic lineage) can influence the frequency of twinning. Although many studies have shown the effect of season on twinning, the scientific literature is still contradictory. Objectives: The aim of our study was to calculate the number and ratio of twin births in 5 typical Holstein-Friesian dairy farms in Hungary. In addition, our goal was to determine whether twinning is influenced by the season and farm. Materials and Methods: In this study, the effect of season on twin calving was evaluated in 5 Holstein-Friesian dairy herds retrospectively. Data have been collected between years 2001-2010 with the well-known and commercially available "RISKA" management software. A total of 31 234 deliveries have been evaluated. Effect of the season and farm has been evaluated with the chi-squared test. Results and Discussion: Our results revealed that most of the twin births could be observed during the summer (rho = 0.002); the causatives are still questionable, but one possible cause can be that during the fall months, the weather is colder, and the summer heat stress is over. During the study period, 1281 (3.94%) twin births occurred. The ratio of twin deliveries on the farms varied between 3.43-4.35%. Further large scale studies are needed. Dairy cattle breeders should develop strategies to manage twinning.