This article presents the results of research into the reproductive performance of Swiss cows kept year-round in open-air paddocks. The study was conducted at the Private Enterprise «Agro-Novoselivka 2009» of Kharkiv District, Kharkiv Region, during 2023–2025. It has been established that the reproductive performance of dairy cows is influenced by a range of factors, including breed and genetic characteristics, the animals’ age, the regularity of oestrus, the duration of the inter-calving and service periods, fertility rates, the housing system, and the so-called «farm effect». It was found that, due to their high biological plasticity and good acclimatisation ability in the eastern part of the Forest-Steppe zone of Ukraine, Swiss cows exhibited high milk production rates in both their first lactation (8215,6 kg) and second lactation (8810,2 kg). At the same time, the cows’ adaptation index was negative, standing at -2,85 and -1,93 units respectively, which deviates slightly from the optimal level (0,0) and indicates a slight imbalance between the environmental conditions and the organism of the experimental animals. It was found that the insemination index for Swiss cows was relatively low, and in the second lactation it decreased by 8,8 % (P<0,05) to 2,28. In first-lactation cows, the service interval lasted 117,9 days, whereas in the second lactation this figure decreased by 8,5 days, or 7,9 % (P<0,05). A trend was observed towards a correlation between a decrease in the insemination index and a reduction in the duration of the service period: as the insemination index decreased by 8,8 % in the second lactation, the duration of the service period was reduced by 7,9 %. At the same time, a 7,9 % reduction in the duration of the service interval during the second lactation was accompanied by a 7,2 % increase in the milk yield of the cows. It was established that the duration of the intercalving period (ICP) in Swiss cows during the first lactation was 404,1 days, whilst during the second lactation it was 2,1 % shorter, although this difference was not statistically significant. Accordingly, the reproductive efficiency coefficient, which directly depends on the duration of the intercalving period, was 0,90 during the first lactation and 2,2 % higher during the second. The reproductive efficiency coefficients obtained for both lactations were close to the optimal level of 1,0. The duration of the dry period in the experimental cows in both lactations was within the optimal range and amounted to 66,4 and 64,5 days, respectively. Thus, when kept in open-air paddocks, Swiss cows have adapted well to the husbandry and climatic conditions and demonstrate a relatively high level of reproductive performance. The results obtained are consistent with the biological characteristics of this breed and ensure that their high productive potential is realised.

Keywords: cows, Swiss breed, reproductive performance, service interval, dry period, intercalving interval, insemination index, husbandry, open-air paddocks.