Relation between growth rate, serum somatomedin and plasma testosterone in young bulls.

Twenty "Red Danish" bulls were tested for rate of gain, linear growth, longissimus muscle area and efficiency of feed utilization from the age of l 'h to 12 months. These variables were correlated to blood concentrations of testosterone and somatomedin, which were measured at 4 to 5 months, 6 to 7 months and/or 8 to 10 months of age. Average testosterone concentrations of bulls above 6 months of age were found to be correlated negatively (P<.05) with feed utilization (feed units/kg gain). Average somatomedin activities throughout the test period were positively correlated with rate of gain (P<.05) and linear growth (P<.05), and negatively to feed utilization (P<.05). Also, the somatomedin activity was found to increase significantly from 6 to 7 months up to 10 months of age (P<.05). No significant correlation between testosterone and rate of gain, linear growth or longissimus muscle area was found, and, likewise, there was no significant correlation between somatomedin activity and longissimus muscle area. It is concluded that the blood level of somatomedin at an early age may represent a possible indicator of future growth capacity in young bulls. (