Abstract. The aim of the work is to determine influence of factors, such as breed, age, belonging to the line, on the duration of lactation of cows, as well as identify a influence degree of the average daily milk yield and the month of lactation of a cow on the probability of fruitful insemination. The research was carried out on the basis of the breeding reproducer of OOO “Polyarnaya Zvezda” in the Murmansk Oblast on the number of cows of different ages of the Holstein breed of black-and-white suit and the Ayrshire breed. Such studies on cows with milk yield of 8,000-10,000 kg of milk were carried out in the Far North for the first time. The influence of paratypical and genotypic factors on the duration of lactation was studied. A two-factor variance analysis was conducted to determine the effect of the average daily yield and the month of lactation of the Holstein cows of black-and-white suit on the probability of fruitful insemination. The work reveals that it is not profitable for a farm to have animals with both shortened and elongated lactation. The level of productivity of cows with shortened lactation is significantly lower than of the ones with optimal lactation. Elongated lactation is not economically feasible, as it leads to violation of the reproduction plan in the economy. The influence of the breed on the duration of lactation was determined. Representatives of the Ayrshire breed are less prone to shortened lactations than of the Holstein. The age of cow also affects the duration of lactation. Cows of the second calving have best indicators – of 610 heads 80.8% reached full lactation. The highest percentage of cows that completed lactation early because of culling was observed among full-aged animals – 47.7%. According to the two-factor analysis results, the daily milk yield value has a low impact on the probability of fruitful insemination (0.003). The combined effect of the average daily milk yield and lactation month are important (0.03). The research results can be used to improve the efficiency of breeding work with dairy cattle and will further predict qualitative changes in animals
Keywords
milk production, average daily milk yield, duration of lactation, cattle breeds