The article presents the results of research on the reproductive ability of Brown Swiss cows in conditions of year-round maintenance on open-air yards. the study was conducted in the Agronovoselivka 2009 private enterprise of the Kharkiv district, Kharkiv region in 2023–2025. It was determined that the reproductive ability of dairy cows depends on a number of factors: breed, heredity, age, regularity of estrus, calving interval and service period, fertilization, housing system and the so-called «farm effect». It was established that Swiss breed cows, due to their high biological plasticity and good acclimatization ability in the climatic conditions of the Forest-Steppe in eastern Ukraine, showed high milk productivity in both the first (8210 kg) and second lactation (8815 kg). At the same time, the adaptation index of cows was negative and was at the level of ˗2,85 units and -1,93, respectively, which is not much less than the optimal level (0,0) and indicates a slight imbalance between the external environment and the organism of the experimental animals. It was proven that the insemination index was not high enough, but in the second lactation it decreased by 8,8 % (P<0.05) and amounted to 2,28. In experimental cows, the service period after the fi rst lactation was 117,9 days, after the second – by 8,5 days or 7,9 % shorter (P><0,05). A trend was estab lished that with a decrease in the insemination index in the second lactation by 8,8 %, the service period was reduced by 7,9 %. And a decrease in the service period by 7,9 % in the second lactation led to an in crease in the productivity of cows by 7,2 %. It was determined that after the first lactation, the calving interval was 404,1 days, after the sec ond – by 2,1 %, not signifi cantly less. Accordingly, the coeffi cient of reproductive ability, which directly > <0.05) and amounted to 2,28. In experimental cows, the service period after the first lactation was 117,9 days, after the second – by 8,5 days or 7,9 % shorter (P<0,05). A trend was estab lished that with a decrease in the insemination index in the second lactation by 8,8 %, the service period was reduced by 7,9 %. And a decrease in the service period by 7,9 % in the second lactation led to an in crease in the productivity of cows by 7,2 %.> <0,05). A trend was established that with a decrease in the insemination index in the second lactation by 8,8 %, the service period was reduced by 7,9 %. And a decrease in the service period by 7,9 % in the second lactation led to an increase in the productivity of cows by 7,2 %. It was determined that after the first lactation, the calving interval was 404,1 days, after the second – by 2,1 %, not significantly less. Accordingly, the coefficient of reproductive ability, which directly depends on the duration of the intercalary period after the first lactation, was 0,90, and after the second by 2,2 % more. That is, both of them approached the optimal level, to 1,0. The dry period of the experimental cows during both lactations was within the optimal value and was 66,4 and 64,5 days, respectively. So, when kept in open pastures, animals of the Swiss breed are characterized by quite high reproductive indicators, which fully correspond to their biological characteristics.

Keywords: cows, Brown Swiss breed, reproductive ability, service period, dry period, calving interval, insemination index, housing, open-air yards.