REPRODUCTIVE ABILITY OF UNEVEN-AGED HOLSTEIN COWS
A retrospective analysis was carried out into reproductive ability of uneven-aged Holstein cows under conditions of commercial milk production against a background of hormonal stimulation of heat and synchronization of ovulation. It was found that inter-calving periods in high-producing Holstein cows intensively exploited were longer than a physiologically grounded norm (395 days) that was caused by prolonged service and lactation periods by 30 and 27-45 days, respectively. The duration of pregnancy in animals was within the physiological norm and lasted 285.3 days. In turn, the dry period averaged 51.3 days across a herd that was conditioned by technological requirements. It was proved that fertility rate in high-producing cow herd did not practically depend on the cow's age and considerably varied throughout the productive use. Fertilization index in Holstein cows had pronounced age dependency: 2.37 inseminations in cows in first lactation, and 2.09 on the average in cows in second and third lactations that was significantly less than indices in young cows by 11.8 percent (p < 0.001), The cows in forth lactation had the index of 1.91 on the average.