Productive and functional traits of first-calf heifers of three genotypes by different systems of milking

The aim of the study was to identify the most promising genotypes of the Simmental breed for its genetic improvement. Between 2019 and 2022, groups of analog pairs were formed from first-calf heifers of three genotypes at a Simmental breeding farm in the Kursk region, based on the proportion of Simmental (SIM), Montbéliarde (MB), and Holstein (HOL) breeds (genotypes: 25%SIM75%HOL; 50%SIM50%HOL; and 50%MB25%SIM25%HOL). Each genotype group consisted of 140 animals milked with robotic systems and 70 animals milked using a linear milking system (LMS). Body condition was assessed during weighing (n = 20). The animals’ response to a stimulus was measured (n = 20) with five repetitions. The insemination index was calculated based on zootechnical records as the ratio of total inseminations to successful ones. It was found that live weight and body condition were higher in the daughters of MB bulls: by 15 kg (p<0.05) and 0.68 points (p><0.01) during robotic milking, and by 8 kg (p><0.05) and 0.75 points (p><0.01) on the LMS, compared to peers of the 25%SIM75%HOL genotype. The insemination indices of daughters of MB bulls and first-calf heifers with 50%HOL blood were better than those of animals with 25%SIM75%HOL by 0.17 (p><0.001) and 0.13 (p><0.001) during robotic milking, and by 0.34 (p><0.001) and 0.31 > < 0.05) and 0.68 points (p < 0.01) during robotic milking, and by 8 kg (p < 0.05) and 0.75 points (p < 0.01) on the LMS, compared to peers of the 25%SIM75%HOL genotype. The insemination indices of daughters of MB bulls and first-calf heifers with 50%HOL blood were better than those of animals with 25%SIM75%HOL by 0.17 (p < 0.001) and 0.13 (p < 0.001) during robotic milking, and by 0.34 (p < 0.001) and 0.31 (p < 0.001) on the LMS. In terms of combined milk fat and protein yield, the daughters of MB bulls outperformed peers of the 25%SIM75%HOL and 50%SIM50%HOL genotypes by 31.3 and 55.6 kg, respectively, during robotic milking, and by 39.9 and 54.8 kg, respectively, on the LMS. Animals with 75%HOL blood showed a stronger reaction to stimuli – 22 and 16 % higher during robotic milking, and 23 and 16 % higher on the LMS—compared to peers with 50%SIM50%HOL and 50%MB25%SIM25%HOL genotypes. Culling rates after the first lactation under robotic milking were 8 % for cows with 50 and 75%HOL blood (5 % for daughters of MB bulls), and under LMS: 21 % for 75%HOL, 15 % for 50%SIM50%HOL, and 16% for 50%MB25%SIM25%HOL genotypes. Therefore, the 50%MB25%SIM25%HOL genotype is considered the most promising for improving the Simmental breed, compared to 25%SIM75%HOL and 50%SIM50%HOL genotypes, due to superior results in: combined milk fat and protein yield (robotic milking: +31.3 and +55.6 kg; LMS: +39.9 and +54.8 kg), insemination index (-0.17 and -0.04; -0.34 and +0.03), body condition (+0.75 and +0.21; +0.68 and +0.18 points), reaction to stimuli (-23 and -16 %; -22 and -7 %), and lower culling rates after the first lactation (-3 and -3 %; -5 and +1 %, respectively).