Sex, age and breed related changes in bovine testosterone and intramuscular collagen.

Longissimus muscle biopsies were obtained from forty bulls and steers representing Charolais, Simmental, Angus and Hereford breeds at 6, 9, 12, 15 and 18 months of age to evaluate the influence of age, breed and sex on the biosynthesis of muscle collagen. Blood samples were collected from each animal at each time period. The blood serum was harvested and assayed for concentrations of testosterone. Total collagen, soluble collagen and insoluble collagen were obtained on each sample. Soluble collagen and testosterone levels were significantly influenced by breed, sex and animal age. Total collagen levels were significantly affected by sex and age. Total collagen and testosterone levels peaked at 12 months of age. Breeds were ranked identically for total collagen and testosterone levels at 12 months. These data indicate that bulls are different from steers in synthesis of intramuscular collagen at or near 12 months of age. The increased synthesis of collagen appears to be influenced by testosterone or some other event associated with puberty. The mechanism of this action remains unclear.