Evaluation of the associations of PIT-1 and PRL genes with milk productivity and analysis of the conditions for statistical confirmation of differences in cows of the red steppe breed

The aim of this study was to characterize the polymorphism of the PIT-1 and PRL loci in Red Steppe cattle herds of the Republic of Dagestan and to assess the levels of variability in production traits at which differences between genotypes could be statistically confirmed. Genotyping of 48 cows was performed using the PCR-RFLP method (PIT-1/HinfI; PRL/RsaI) with a reproducible thermocycling and restriction protocol. For PIT-1, the following genotype groups were formed: AA (n = 11), AB (n = 16), BB (n = 20); for PRL: AA (n = 34), AB (n = 11), BB (n = 2). Considering the family structure (daughters of the same sire) and the absence of individual productivity records, formal comparisons were replaced by a sensitivity analysis: thresholds of SD and CV (for p < 0.05 and power ~80%) were calculated for milk yield, fat percentage, and protein percentage for all pairwise genotype contrasts within each locus, as well as their medians per locus. Genotyping results indicate that for milk yield, confirmation of differences is possible under moderate variability, with lower CV and SD requirements for PRL than for PIT-1; for fat percentage, the requirements are also moderate. For milk protein percentage, given typical production variance, significant differences are unlikely and would require larger sample sizes. The obtained thresholds can serve as practical guidelines for planning statistical power in future studies and for integrating these markers into breeding programs at the farm level.

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