To determine the influence of various factors on the milk yield of cows, we used a linear model of a mixed type, as a random factor, the genotype of a bull-producer, and as fixed – the number of lactation, the year of birth and the calving season of cows. In total, data on 526 lactations per 113 red steppe cows were included in the analysis, which were kept in the conditions of State Enterprise “Plepreproductor” Stepnoe “(Ukraine, Mykolayiv region) during 2001-2014.
Data on milk yield for ten months (M1-M10) and 305 days of lactation (Y305) were used as a dependent variable. For individual gradations of factors, the estimates of the coefficients with the employer of the LSM procedure (Least squares means ± SE) were computed in the model, and the level of reliability of their deviation from zero (p-estimation) was determined. All calculations were carried out using the module “GLM” (General Linear Model) of the MiniTab software package v. 15.
We have established an insignificant, but it is possible that some bulls-producers influence the hopes of their daughters during M2 … M4. Thus, it was found that the milk of the Altea was lower for the M2-M3 daughters, whereas the milk yield for M2 … M4 in the daughters of the bull of Narcissus was, on the contrary, higher than the average population value. In addition, the last almost 130 kg prevailed in relation to milk yield for 305 days of lactation.
The first-borns were characterized by less milking during the first half of the lactation (especially, according to M1-M2), and by 416 kg inferior to the average population estimate. On the other hand, cows at the age of eighth lactation, on the contrary, showed significantly higher milk yield during the average lactation months (M4 … M8), and an average population estimate prevailed on 662 kg of milk.
In addition, a high level of milk productivity was established for cows born in 2005, 2007 and 2009, which is primarily due to the increase in their milk productivity in the first half of lactation.
The presence of a highly probable effect of the calving season on the level of milk productivity of cows is manifested primarily in the increase in milk yields (especially in M4 … M8) in January calving, and, conversely, in decline – with calving in June and July.
Keyword: Linear models, number of lactation, year of birth, season of calving, dairy cattle.
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