В. М. Гукежев This study analyzes key fertility indicators, specifically the service and interbody periods, which are limiting factors in reproduction rate. This study is relevant because it quantifies hidden offspring losses due to cow mortality, allowing for a more accurate assessment of potential offspring production within the herd. The research aims to determine the impact of age variability on fertility and to quantify hidden offspring losses associated with younger cows in a high-producing dairy herd. The study’s novelty lies in its analysis of the relationship between service period length, cow age, and milk yield, which are key indicators of reproductive performance. The study employs zootechnical, statistical, and comparative analysis methods. The introduction of red-white Holstein bulls to improve the productive and technological traits of the red steppe breed negatively impacted the reproductive performance of the breeding stock. Analysis of age variability in key breeding selection criteria revealed that the longest service and interbody periods occurred during the first two lactations. While these indicators slightly decrease with age, they stabilize at 115–120 days, preventing annual offspring production. Furthermore, cows with more than three calves constitute only 18–20% of the herd. The correlation between milk yield and service period is positive, decreasing with age from 0.29 to 0.09. A considerable proportion of cows (35.8%) and heifers (24.7%) require 3–4 inseminations for successful fertilization. Future research should consider the proportion of abortions and stillbirths, the offspring sex ratio, and their impact on milk yield and service period. Furthermore, investigating the proportion of culls within the first two lactations when using red-white Holstein bulls, considering paternal lineage, would help determine the overall suitability of their use.
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