Investigation of factors affecting growth performance and Kleiber ratio in Angus calves during the pre-weaning period under intensive conditions

This study investigated the effects of genetic, physiological, and fixed factors on the growth performance of Angus calves from birth to weaning under an intensive fattening system for six months. Data on birth weight (BW), weaning weight (WW), average daily weight gain (ADWG), and Kleiber ratio (KR) were collected from a total of 158 Angus calves born in 2011. Management conditions were kept uniform, although specific environmental parameters were not directly measured. Calves were kept with their dams for six months post-birth and were fed grower feed, clean water, and alfalfa hay in areas accessible only to the calves. Data were analyzed using a Generalized Linear Model (GLM) including fixed effects of sex, birth month, dam age, calving interval, and gestation length. The analysis revealed that BW and WW were significantly influenced by sex, gestation length, and dam age (P < 0.05). ADWG was significantly affected by gestation length and sex (P < 0.05). KR differed significantly only by calf sex (P < 0.001) with male calves exhibiting higher growth efficiency than females. Furthermore, the relationship between KR and BW varied by sex, indicating that sex interacts with metabolic efficiency. Overall, these findings highlight KR as a reliable indicator of individual growth efficiency, which can guide early selection, optimize feeding programs, and improve herd management practices. These results highlight the potential of KR as a practical tool for evaluating growth efficiency and supporting herd management decisions in intensive systems.