Effect of single and multiple pregnancies on performance of primiparous and multiparous cows

Data on 393 002 parturitions and performance in the following production cycle were collected from the SYMLEK database for 145 457 Polish Holstein-Friesian cows representing the active population in the Pomorze and Kujawy regions. The animals first calved during 2000–2012 and were used or culled by the end of 2013. GLM and FREQ procedures of the SAS package were used for the statistical calculations. The frequency of twin and triplet births depended on the cow's age (0.64% in primiparous and 2.88% in multiparous cows), calving season (1.79% in winter, 2.41% in summer), previous lactation milk yield (increase of 2.15 to 3.73% with increasing milk production level), and year of calving of primiparous cows (increase from 0.43% during 2000–2003 to 0.78% during 2010–2012). Dams of twins were superior to dams of singles in terms of milk yield, but a significant difference was manifest only in multiparous cows. Despite the higher perinatal mortality of the twins and triplets (especially those born to primiparous cows), multiple pregnancy resulted in a greater number of calves born compared to single pregnancy. A negative effect of multiple pregnancies was a decrease in fertility, especially in multiparous cows (e.g. calving interval was longer by 18 days, reproductive rest period by 9 days, and service period by 10 days, while services per conception increased by 0.15). In addition, twin pregnancy (especially in heifers) and triplet pregnancy (especially in cows) considerably decreased chance of survival until the next calving