The influence of birth season on the growing of heifers and their further productivity

The results of studies on the effect of the birth season factor on the lifetime productivity and growth rate of cows are presented. The material for the research was the information database of the "Selex" breeding record program for the highly productive herd of black-motley cattle of the "Pre-Baikal type". The research was carried out under the conditions of the Irkutsk region in 20152019. Replacement heifers, which were evaluated for growth and development, and subsequently for milk production during the 1st and 3rd lactations and lifetime production, were chosen as an object of research. Heifers born in the summer-autumn period, according to the 1st lactation, gave the highest productivity, their milk yield was 6151-6179 kg of milk with a fat content of 3.85%. By the 3rd lactation, cows born in the summer months retained high productivity (7001 kg with a milk fat content of 3.83%). From the cows born in winter, a maximum lifetime production of 30,519 kg was obtained. The cows born in spring have 856 kg less lifetime productivity. With the maximum lifelong productivity, the age in lactations was 4.5, with the minimum - 4.0. This indicates that the shorter the period of productive use, the lower the lifetime milk yield of cows. The cows that gave the highest milk production in the first lactations dropped out of the herd sooner for various reasons, thereby not having reached their full genetic potential and not having shown their possible maximum milk production.