|Spiers, Donald - UNIVERSITY OF MISSOURI|
|Eichen, Peggy - UNIVERSITY OF MISSOURI|
|Byatt, J. - MONSANTO AGRICULTURAL CO.|
Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: July 26, 1995
Publication Date: N/A
Technical Abstract: Studies were conducted to determine if recombinant bovine somatotropin (rBST) is capable of improving growth performance of heat-challenged rats when administered during rapid development prior to puberty. Sprague- Dawley female rats (50 d of age) were placed in thermoneutral (TN; 21 deg C) or heat-challenge (HC; 31 deg C) environments. After 7 d, rats were injected with either rBST (20 mg/day/kg body weight) or sterile water. Al injections were for a 10-d period. Body mass and food consumption were measured daily prior to and during this period. Resting metabolic rate and body temperatures were determined on the last injection day, followed one day later by determinations of fat free mass (FFM), total body water (TBW), and mass of selected organs. Food intake relative to body mass (FI) of HC rats was less than for TN rats on the first day prior to injection (P<.001). As a result, body mass of HC rats on the first day of injection was 18 g below TN rats (P<.001). FI of HC-injected rats was below TN valu (P<.001) even on the last treatment day. Treatment with rBST increased growth rate of HC and TN rats (5 g ADG) above control level (3 g ADG), with first group differences between body mass on d 5 (P<.03) for TN rats and d 3 (P<.02) for HC rats. Organ masses relative to body mass were not different for treatment or ambient temperature groups. In addition, there were no treatment differences in FFM or TBW relative to body mass. Although resting metabolic rate decreased (P<.01) and rectal temperature increased (P<.01) from 21 to 31 deg C ambient temperature, there was no effect of rBST treatment on these values. The results show that treatment of prepubertal, heat-challenged rats with rBST counteracts heat-induced depression of growth rate without altering food intake or body composition.