The effect of IGF-1 gene polymorphism on dairy productivity and reproductive qualities of Holstein cattle in the Republic of Tatarstan

The article presents the results of a comprehensive study on the effect of polymorphism in the insulin-like growth factor 1 (IGF-1) gene on key economically valuable traits in Holstein cattle of domestic selection in the conditions of the Republic of Tatarstan. Three genotypes were identified at the studied locus: AA, AB, and BB. The population was characterized by moderate genetic diversity with an allele A frequency of 0.524 and allele B frequency of 0.476, with the genotype distribution showing a slight deviation from Hardy-Weinberg equilibrium. It was found that the heterozygous AB genotype is associated with the highest overall milk productivity indicators. Individuals with this genotype demonstrated the highest milk yield both for complete lactation (7399.0 kg) and standard lactation (7232.0 kg), indicating a heterosis effect. In addition, heterozygous cows had the highest percentage of milk fat (3.58%) and maximum total milk fat yield. At the same time, animals with the homozygous BB genotype showed pronounced advantages in reproductive traits. They showed a higher reproductive ability index (0.98) and the lowest barren rate (11.5%), which indicates better fertility and reproductive efficiency of the herd. It is important to note that cows with the BB genotype also exhibited optimal sanitary and hygienic properties of milk, as confirmed by a significantly lower somatic cell count (277.8 thou./cm³) compared to other groups. This fact indicates potentially greater resistance to mastitis and higher milk product quality. Individuals with the homozygous AA genotype of the IGF-1 gene lagged behind in most studied parameters, displaying the shortest lactation duration and total lactation yield. Thus, the heterozygous AB genotype is preferable for maximizing milk yield and milk fat content, while the BB genotype is advisable to use to improve reproduction, udder health, and milk quality.

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