The role of fixed factors in the variability of milk yield in Irmeni cattle under industrial complex conditions

Abstract

The authors evaluated the significance of paratypic factors in fat variability in the article. The study looked at the role of fixed effects such as: “Calving Season”, “Calving Year”, “Starting Season”, “Starting Year” and their interacting factors: “Calving Season: Calving Year”, “Starting Season: Starting Year”, “Calving Season: Starting Season”, “Calving Year: Starting Year”. The authors used data from Irmen’s primary zootechnical census of black-and-white cattle (n = 319210) from 2000 to 2020. The role of genetic and paratypical factors was assessed using linear mixed regression models and appropriate statistical methods and criteria. The following were selected as random effects: father, age of fertile insemination and animal identification data. The influence of the fixed characteristics of the prospective mathematical model was evaluated using an analysis of variance. But beforehand, the authors identified different combinations with adjustment for the proportion of random contribution. The grant levels of the estimated factors to the variability of the dependent trait were determined. The authors note the high conjugate variability between predicted and actual milk yields (r = 0,905; p˂ 0,001). A relatively high coefficient of determination (R2 = 0,819) was observed for the test sample. In this case, only phenotypic data were considered in the example when constructing the model. Application of the resulting model to other subpopulations may require additional correction factors as part of regional or federal breeding value index programs.