Effect of pituitary somatotropin injections on plasma insulin-like growth factor I and somatotropin profiles in growing heifers.
Effects of daily injections of pituitary-derived bovine somatotropin (bST) for 6 wk were evaluated in 10 growing heifers and compared to 9 placebo-treated control animals. Bovine somatotropin was injected at 50 micrograms/kg BW each day. Body weight and growth, plasma concentrations of insulin-like growth factor I (IGF-I) and somatotropin (ST) were assessed. To measure plasma concentrations of IGF-I, we validated a RIA in which bovine plasma samples were extracted with acid-ethanol, a method that resulted in greater than 90% recovery of IGF-I. Average daily gain was similar during the first 4 wk of the experiment in both control and bST-treated groups; however, at the end of the experimental period (wk 4 and 6) ADG was greater (P less than .05) in bST-treated heifers (1.24 +/- .21 kg/d vs .75 +/- .25 kg/d). Plasma IGF-I from wk 2 to wk 6 were increased in bST-treated animals (452 +/- 97 ng/ml at wk 2; 683 +/- 106 ng/ml at wk 6) compared with controls (293 +/- 62 ng/ml at wk 2 (P less than .01) and 293 +/- 115 ng/ml at wk 6 (P less than .001). Moreover, ADG over the 6-wk experimental period was correlated with mean IGF-I concentrations determined over the same period (r = .55; P less than .01). As expected, mean plasma ST concentrations were increased in bST-injected animals from wk 1 to 6. Gel chromatographic profiles of bovine plasma exhibit a 150,000 molecular weight ST-dependent binding protein-IGF-I complex and a 30,000 molecular weight non-ST-dependent complex. This study validates a method for measuring IGF-I in cattle, and shows a positive relationship among IGF-I and ADG after ST treatment. No correlation, however, was found between plasma ST and growth performance.
Lemal
D
D
Faculty of Agronomy, Gembloux, Belgium.
Renaville
R
R
Claes
V
V
Ruelle
L
L
Fabry
J
J
Burny
A
A
Underwood
L E
LE
Ketelslegers
J M
JM
D000818:Animals; D002417:Cattle / Q000097:blood* / Q000254:growth & development; D002850:Chromatography, Gel; D004305:Dose-Response Relationship, Drug; D005260:Female; D013006:Growth Hormone / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D007279:Injections, Subcutaneous / Q000662:veterinary; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D011863:Radioimmunoassay; D013002:Somatomedins; D015430:Weight Gain / Q000187:drug effects
D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone