Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 23, 1998
Publication Date: N/A
Interpretive Summary: The growth promoting mechanism attributable to the antibiotic chlortetracycline in not known. A feeding study was conducted with growing beef steers to determine the effects of sub-therapeutic oral chlortetracycline under conditions of limited (10%) and adequate (13%) dietary protein on plasma insulin-like growth factor-1 concentration and concurrently on performance and carcass merit. Sustained effects of sub-therapeutic feeding of chlortetracycline in cattle appears to not increase insulin-like growth factor-1 status, but to increase fat deposition consistent with a reduced growth hormone and thyroid status under limited or adequate protein conditions as described in a separate report. This would tend to increase energy utilization but may not necessarily produce a measurable increase in weight gain. Evidence is provided that indicates chlortetracycline may increase plasma insulin-like such as adapting to feedlot management and diets, suggesting that reduced concentrations of insulin-like growth factor-1 may be an early indicator of immune stress in cattle.
Technical Abstract: This study was conducted to determine the effects of feeding a sub-therapeu of dietary protein (PRO; 10% and 13% of diet DM) on plasma insulin-like growth factor-1(IGF-1) concentrations and concurrent growth performance and carcass merit. Thirty-two steers (initial weight, 286 kg) were adapted to a common 13% protein diet consisting primarily of grass hay, corn, and soybean meal fed to gain 1.3 kg/d. The steers were assigned to four treatments (- or + CTC and 10% or 13% PRO in a factorial arrangement) and fed ad libitum amounts of diet for 91 d. Jugular blood samples for plasma IGF-1 analysis were obtained at 0, 7, 14, 28, 56, and 84 d. Steers were killed at the end of the feeding period for carcass merit evaluation. Based on IGF-1 concentrations, d 0 to 28 appeared to be a period of adaptation to diet and intake level and d 29 to 91 reflected sustained effects of treatment. The sustained effect of sub-therapeutic feeding of CTC to cattle appears not to increase IGF-1 status, but to increase fat deposition consistent with reduced growth hormone and thyroid status. This would tend to increase energy utilization but may not necessarily produce a measurable increase in weight gain. Chlortetracycline may be beneficial during short-term adaptation periods such as when cattle are received at a feedlot and adapted to feedlot management and diets. Under these circumstances, feeding a sub-therapeutic level of CTC may result in increased plasma IGF-1 concentrations.