Influence of the age at the first insemination on the productive longevity of black and white and kholmogory cows
The influence of the age at the first fruitful insemination on the productive longevity of the black-and-white and Kholmogory cows in Udmurt republic was analysed. The study results are presented in the paper. The economic use period of the study cows did not have statistical differences and lasted 3,42-3,43 lactation periods. Black-and-white cows exceeded Kholmogory cows in the lifetime milk yield (by 3416,5 kg), fat content in milk (by 0,47 %) and milk amount in terms of basic standards (by 6317,7 kg) (P > 0,999). The optimal age for the first insemination of black-and-white cows can be considered 16-17 months, since insemination at the specified age ensures highest longevity in cows (3,85 lactations) and the highest lifetime milk yield indices (21347,8 kg), also expressed in terms of basic standards (27065,6 kg). Too early insemination of the black-and-white cows (up to 15 months) is not recommended, as it results in the decreased lifetime milk yields (up to 15491,4 kg), fat and protein content and shortens the economic use period of the animals up to 3,33 lactation periods. The lowest longevity (3,07 lactation periods) was observed in the black-and-white cows inseminated at the age of more than 20 months. The Kholmogory cows demonstrated an increase in lifetime milk yields (1084,5 kg (P > 0,95)) and the economic use period (1,05 lactation period (P > 0,999)) when the age of the first insemination was increased. However, as the fat mass ratio in milk decreased (by 0,06 % (P > 0,999)) and the protein mass ratio in milk fell (by 0,02 % (P > 0,999)), the increase in lifetime milk yield in terms of basic standards resulted from the increase in the age of the first insemination has no significant differences.