DAIRY PRODUCTIVITY OF FIRST COWS WITH DIFFERENT GENOTYPES BY GROWTH GENE
The aim of the study was to study the allelic polymorphism of the growth hormone gene in a group of cows of the Montbeliard breed and to search for associations of its different genotypes with the parameters of the dynamics of milk yield during lactation. The research was conducted in the Department of Animal Genetics and Biotechnology of the Institute of Animal Breeding and Genetics of NAAS on a group of 30 cows of the Montbeliard cattle breed from PSP "Zhadkivske" of Chernihiv region. Genomic DNA was isolated from blood leukocytes by standard methods using the set "DNA-sorb-B" ("Ampli-Sense", Russia). Dairy productivity of first-born cows was determined monthly by control milkings. Types of lactation curves were studied according to the method of A. S. Emelyanov (1953). Polymorphism of the growth hormone (GH) gene in our first-born cows is represented by two alleles L I V, the frequency of which differs, and the frequencies of genotypes differ accordingly.
In the studied group of animals, all possible genotypes of the growth hormone gene were identified: 25 animals (83%) have the GHLL genotype, 4 (13%) have the GHLV genotype, and only one cow has the GHVV genotype. The frequency of the L allele is 0.9, and the V allele is 0.1. The mean expectation for 305 days of the first lactation of a group of cows with the GHLL genotype was 352 kg higher than the expectations in the group of heterozygous cows with the GHLV genotype. In terms of milk fat and protein yield, cows with GHLL genotype were significantly dominated by cows with GHLV genotypes (74 kg fat and 36 kg protein, respectively, p < 0.001). Analysis of the dynamics of monthly milk yield of the studied cows for 305 days of the first lactation showed that the productivity of cows with GHLL genotype exceeds the average monthly milk yield of other groups of animals at the beginning (from 1 to 3 months), at the peak of lactation (4th month) and at the end of lactation (from 8 to 10 months). In general, during the 305 days of the first lactation, first-borns with the GHLL genotype had better milk yields compared to their peers with other growth hormone gene genotypes. Analysis of variance showed that the obtained share of variability in milking in animals with different genotypes of the GH gene is due to random factors.
Analysis of lactation curves of primiparous women showed that milk yield of cows with all variants of genotypes in the GH gene gradually increased and reached its peak at 3–4 months of lactation, and then gradually decreased. This lactation curve, according to the classification of A. S. Emelyanov is characteristic of animals with high and stable lactation, and cows are able to digest food well and produce high hopes. \
Thus, a statistically significant difference in quantitative and qualitative characteristics of milk productivity of cows of Montbeliard breed with different variants of genotypes by GH gene on the example of a group of cows from "Zhadkivske" Chernihiv region suggests that the use of genetic markers, in particular the growth hormone GH selection of selection and further formation of the herd in the direction of increasing milk productivity.
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