The effects of bovine recombinant growth hormone administration on insulin-like growth factor-I and the haemopoietic system in thoroughbred geldings

The effect of intramuscularly administered recombinant bovine growth hormon e (rbGH) on insulin-like growth factor-I (IGF-I) and white and red blood ce ll indices was studied in Thoroughbred geldings. An insulin-like growth fac tor binding protein (IGFBP)-blocked radioimmunoassay was modified and valid ated for the measurement of IGF-I in equine blood plasma. Baseline values o f IGF-I and blood indices were determined over a 48 h period and then a sin gle dose of 5 mu g/kg, 10 mu g/kg or 50 mu g/kg of rbGH was administered. I nsulin-like growth factor-I levels increased in a dose-dependent manner, wi th the highest values between 12 h and 24 h. The highest dose (50 mu g/kg) yielded the greatest IGF-I response with a 90.2 +/- 10.8% increase at 24 h. White blood cell count increased following the three doses of rbGH with th e highest white blood cell count at 12 h after the 50 mu g/kg dose. Haemogl obin was significantly increased at 24 h (P < 0.05), when values following doses of 10 mu g/kg and 50 mu g/kg were significantly greater than after th e vehicle or the dose of 5 mu g/kg. Red blood cell count was not affected b y any of the rbGH doses. These results indicated that rbGH is biologically active in the horse and that rbGH at a dose rate of 10 mu g/kg or more coul d be used therapeutically. (C) 2000 Harcourt Publishers Ltd.