Evaluation of the relationship between milk yield and the service period duration of cows

Abstract

In the Sverdlovsk Region, the breeding stock of the black-and-white Ural breed was covered with the seed of servicing bulls of Canadian, Danish and German selection. They are able to show good average daily milk yields throughout lactation, to produce for a long time without a sharp decrease in milk yield, but at the same time, the problem of a decrease in the reproductive ability of cows and, as a consequence, a decrease in the productive longevity of the breeding stock was identified. The purpose of the work is to assess the relationship between the indicators of milk yield of Holsteinized black-and-white cattle of the Ural breed and the service period duration. It has been established that milk yield in first-calf cows increases with an increase in live weight to 600-624 kg, and then slightly decreases (P≥0.05). Calculation of the correlation coefficient between the characteristics of milk yield per lactation and live weight of first-calf heifers showed that it is different and varies depending on the live weight of cows from -0.36 for cows with a live weight of less than 550 kg to 0.28 for animals with a live weight of over 625 kg. There was a low positive relationship of these characteristics in cows with live weight of 575-599 kg. On average for the herd, it is positive and is 0.15. The service period for first-calf heifers ranged from 99 days (live weight 550-574 kg) to 162 days (live weight over 625 kg). Large milk yields were observed in animals with live weight of 575-599 kg and a service period of 138-140 days. A positive high and medium correlation between milk yield and the service period duration was established in groups of cows with live weight up to 550 and 575-624 kg and on average for the herd. It is impossible to draw an unambiguous conclusion about the influence of the service period duration on the quality indicators of milk, with the exception of the indicator service period – mass fraction of protein (MFP), where it was negative regardless of the live weight of cows.