Abstract
<jats:p>Amidst increasing domestic beef production, enhancing the efficiency of beef cattle farming and developing cattle breed resources have acquired particular relevance. The objective of this study was to investigate the characteristics of sexual maturation and reproductive function in heifers and first-calf cows of various beef-type Simmental genotypes, as well as to comparatively assess their live weight during key stages of the reproductive cycle. The research was conducted in the Chelyabinsk Region. The field experiment involved the study of four groups of animals: Simmentals of domestic breeding, Herefords, and heifers possessing varying proportions of German and Canadian Simmental bloodlines. The study analyzed age-related parameters regarding the onset of sexual activity, the timing of insemination and calving, and the dynamics of the animals' live weight during different phases of the reproductive cycle. It was established that heifers of the Hereford breed exhibited earlier signs of sexual maturation compared to their Simmental counterparts. Conversely, animals of the Simmental genotype—particularly those with proportions of imported Simmental bloodlines—were distinguished by a higher live weight during the periods of sexual maturation and the active exercise of reproductive function. The highest live weights at the time of successful insemination and prior to calving were recorded in animals possessing German and Canadian Simmental bloodlines. Specifically, contemporaries with an admixture of imported Simmental bloodlines outperformed purebred Simmental and Hereford heifers—whose live weights were comparable during this period—by 33.7–33.2 kg (P < 0.01). During the postpartum period, live weight recovery was observed across all groups; however, Hereford first-calf cows were characterized by a faster rate of recovery. The results obtained indicate the existence of inter-group differences regarding age at sexual maturity and live weight during key stages of the reproductive cycle—factors of critical importance for supporting breeding and selection programs and for enhancing the efficiency of utilizing the beef cattle breeding herd.</jats:p>