Assessment of phenotypic and genetic changes in highly productive Ayrshire cattle

The Leningrad population of the Ayrshire cattle in the Russian Federation is considered the largest in terms of livestock and the most highly productive. Currently, there is an increase in dairy productivity in this population against the background of a reduction in livestock and indicators of productive use of cows. For targeted breeding work related to increasing the lifetime productivity of cows, it is necessary to regularly monitor the genetic changes in these traits. The aim of the research is to study the phenotypic and genetic trend of milk productivity in terms of first lactation, longevity and lifetime productivity of cows in a breeding herd of the Ayrshire cattle. The method of Ch. Smith (1962, 1977) modified by V.M. Kuznetsov (1983) was used to calculate the genetic trend. The phenotypic and genetic trend was calculated based on the periods of repeated use of the seed of the same breeding bulls (n = 12 bulls). We found that the phenotypic trend in all indicators of milk productivity during the first lactation and indicators of productive longevity of cows is positive. For instance, in 2017, 7,472 kg of milk with a fat content of 4.39% and a protein content of 3.33% was produced from lactating first heifers, which is 339 kg, 0.58% and 0.09% more than from first heifers in 2002, respectively, in all cases P ˂ 0.001. A positive genetic trend for the same period per year was established for milk yield for the first lactation (+7.6 kg) and for all signs of productive longevity of cows, total life expectancy (TLE) +15.8 days, lifetime milk yield (LMY) +333 kg, lifetime milk fat (LMF) and lifetime milk protein (LMP) +16.2 and +14.4 kg, respectively. The genetic trend in milk quality (fat and protein) was approaching zero. The rate of genetic improvement, calculated from the average productivity indicators for the herd, for milk yield during the first lactation was 0.1%, according to signs of productive longevity it was higher – 0.8–1.8%.