Characteristics of phenotypic traits of fertility, milk production and survival of Holstein cows depending on the age of the first calving

Purpose: study the phenotypic parameters of fertility, milk production and survival of the same cows during their lifetime in the herd (from birth to the fourth calving) depending on the age of the first calving to better understand the factors that will improve the productive longevity of cows. Material and methods. Studies were conducted in a commercial herd with Holstein cattle located in the Central region of the Russian Federation. For the analysis, we used data from cows (culling and alive) of the same year of birth (2014), which were born, grew, calved and reached 4 calving (2019). The generated database contained complete information about the animal throughout its life in the herd (n=842). Depending on the actual age of the first calving (26 months), which reflects the growth rate, cows were grouped into groups: less than 23 months, 23–25 months, 26–29 months and over 30 months. In each group, we studied (1) reproductive parameters of heifers (number of inseminations per conception, age of the first insemination); (2) reproductive parameters of cows (number of inseminations per conception,, number of days from calving to first insemination, number of days from first to last insemination, conception rate at first insemination, number of days from calving to conception); (3) 305-day milk yield of first, second and third lactations; (4) lifetime milk production; (5) longevity index (proportion of days spent on milk production); (6) survival rate (proportion of cows surviving from first calving to the second, third and fourth calving, respectively).  Results. Cows with an average age of the first calving of 22.1 (<23 months) and 23.7 (23–25 months) months during the growing period with a minimum interval from the first insemination to conception (68 days) had a high percentage of pregnancy from first insemination ≥84%. Survival rates from 1 to 2 calving ranged from 82.7% to 83.1%, to 3 calving-from 55.3% to 62.7%, to 4 calving — from 6.0% to 11.9%, respectively. Optimal intervals between inseminations allowed to finish 3 lactation, in general, 73% of cows and 45% were still alive and producing milk. For 3 lactation (for 305 days) they produced from 17280 to 17805 kg of milk. What was spent on from 45% to 48% of a productive life. Cows with an average age of the first calving of 26.9 (26–29 months) and 32.5 (≤30 months) months during the growing period had a low conception rate of 44% and 5%, long intervals between inseminations (from 113 to 219 days). In lactation, there was a tendency to increase the average days from calving to the first insemination (in 1 lactation — from 85 to 88 days, in 2 lactation — from 82 to 83 days), from the first insemination to conception (in 1 lactation — from 117 to 122 days, in 2 lactation — from 88 to 92 days), which led to an increase in the days from calving to conception (in 1 lactation — from 156 to 164 days, in 2 lactation — from 125 to 140 days). Such cows had the lowest fertility, survival rate, and therefore the short productive life. Conclusion. Cows with the age of the first calving ≤25 months without serious problems during the rearing period were distinguished by the best indicators of reproduction and productivity. They reached the third lactation faster and ended it by producing the largest amount of milk, which spent 45 to 48% of their productive life.