The occurrence of twin calving in Holstein Friesian cattle is 3-5%. Reproductive problems found before and after the time of calving lead to serious economic losses. The authors' aim was to form a compilation of data regarding the cause and effects of twin calving on dairy cows by comparing the reproductive performance of cows before and after calving twins vs. single calves and also analyzing the milk production of dairy cows both before and after twin calving. Cows that would have twins became pregnant earlier, probably because of their better health and fertility, with shorter gestations and calving interval. However, after calving, cows that had twins showed poorer reproductive performance. The results show that twin-calving cows had better condition prior to calving, resulting in an earlier successful twin calving. However, the economic losses during parturition, metabolic disorders of the cow, and low vitality of the twin calves, coupled with the decreased fertility and elevated culling rate in cows after twinning, may discourage breeding twins in dairy cattle.

Introduction. Twin-calving occurs in 3 to 5 % of Holstein Friesian cattle, and it is mostly followed by reproductive and economic problems. This evaluation will compare the service period and the milk yield in cows with single and twin births at a Hungarian large-scale farm. Materials and Methods. The data were collected from 4223 cows between 2000 and 2010. In Cox's regression model (service period) and general linear model (milk production traits), the type of calving (single/twin), the construction code (referring to the Holstein Friesian blood proportion), the season and number of calvings were fixed effects, and furthermore, the year of calving was a covariate. Results and Conclusions. This analysis showed there was no significant difference in the length of service period (SP) between the two groups of cows. The total lactation milk yield produced a meaningful difference in performance: single-calving cows had greater milk yield (p=0.013), fat yield (p=0.030), and protein yield (p=0.028) than cows with twins. The standard lactation milk yield showed the same tendency at a stronger significance and a lower level of production. This unexpected and contradictory result in service period could be explained by the much longer period of open days in twinning DÖRSTELMANN et al.: Multiple birth in cow 113 cows, known from previous research. Regarding milk yield, an involuntary decrease for cows after twin calving was confirmed.