Growth performance and carcass composition of lambs infused for 28 days with a growth hormone-releasing factor analogue.
A human growth hormone-releasing factor analogue, [DesNH2Tyr1,D-Ala2,Ala15]hGRF(1-29)NH2 (GRF-A), was infused s.c. into lambs for 28 d to determine its effects on growth performance and carcass composition. Twenty crossbred wethers weighing 47.0 +/- .5 kg were implanted with 7-d osmotic minipumps at weekly intervals. Minipumps contained either vehicle (dimethyl sulfoxide:H2O, 1:1) or GRF-A, released at a rate of 208 pmol (or .7 micrograms).h-1.kg-1. During the infusion period, plasma GH levels were increased (P less than .01) in GRF-A-treated wethers compared with control wethers (15.0 vs 9.3 ng/ml) and were higher on days that closely followed minipump implantation. Plasma IGF-I and hepatic IGF-I RNA concentrations were similar in lambs of both groups. Analogue treatment improved feed conversion (4.9 vs 5.8 kg dry matter/kg gain, P less than .05), increased average daily gain (.35 vs .30 kg, P = .05) and had no effect on feed intake, wool growth and body, carcass, selected organ and pituitary weights. Carcasses from GRF-A-infused lambs had less adjusted fat depth, a lower percentage of fat and a higher percentage of protein (P less than .05) than carcasses from control lambs. Magnitude of most effects of GRF-A on carcass measurements were correlated with the mean GH level that a lamb had during the infusion period. In conclusion, s.c. infusion of GRF-A improved feed utilization and altered carcass composition of feeder lambs in a relatively short period of time (28 d).
Godfredson
J A
JA
University of Minnesota, St. Paul 55108.
Wheaton
J E
JE
Crooker
B A
BA
Wong
E A
EA
Campbell
R M
RM
Mowles
T F
TF
D000818:Animals; D001823:Body Composition / Q000187:drug effects; D004435:Eating / Q000187:drug effects; D013006:Growth Hormone / Q000097:blood; D013007:Growth Hormone-Releasing Hormone / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D015918:Infusion Pumps, Implantable / Q000662:veterinary; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000235:genetics; D008297:Male; D008460:Meat; D009929:Organ Size / Q000187:drug effects; D010902:Pituitary Gland / Q000187:drug effects; D012313:RNA / Q000032:analysis; D012756:Sheep / Q000033:anatomy & histology / Q000254:growth & development*; D015430:Weight Gain / Q000187:drug effects; D014935:Wool / Q000187:drug effects / Q000254:growth & development
D012313:RNA; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone