Abstract
The aim of the study was to evaluate the effect of 12 complex GN and LEP genotypes on cow productivity in order to identify consistently effective allele combinations that account for genotype-environment interactions, and to develop personalized strategies for herd breeding and management. The conducted study revealed a significant association between complex genotypes of the somatotropin (GH, LV polymorphism) and leptin (LEP, R25C and A80V polymorphisms) genes and milk productivity in Holstein cows. A study of 120 animals (60 animals each from two agricultural organizations) showed a marked uneven distribution of the 12 analyzed genotypes in both herds, due to the farm breeding priorities. A key result was the identification of the GHLVR25CRRA80VAA genotype as the most promising for breeding for high lifetime milk productivity. Animals with this genotype consistently demonstrated maximum milk yields in the first and third lactations and lifetime productivity, demonstrating stability and high genetic potential. In parallel, genotypes associated with milk quality traits were identified. For example, in animals carrying the GHLVR25CCCA80VVV genotype at Organization "K," the lifetime fat and protein content was 3.92 and 3.27 %, respectively. Animals with the GHLVR25CCRA80VAA genotype in Organization "P" had a maximum fat content of 4.13 % while maintaining high milk yield. The study confirmed the critical influence of environmental factors (feeding, management) on the realization of genetic potential. The significantly higher milk yields in Organization "P" compared to Organization "K" highlight the need for a systematic approach combining genetic selection with improved livestock production technologies. The obtained data demonstrate that the complex GH and LEP genotypes serve as informative markers for predicting milk productivity and the adaptive potential of cows.