Growth performance and carcass composition of lambs infused for 28 days with a growth hormone-releasing factor analogue.

Abstract

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).

The effects of short-term recombinant bovine somatotropin treatment on fattening performance, carcass composition and visceral organ weights in karayaka lambs in Turkey

“…Pelvic and internal fat tissue did not change in bST group. This finding is in agreement with previous studies (McLaughlin et al 1994;Godfredson et al 1990;Johnsson et al 1986;Muir et al 1983). Analysis of the carcasses showed some carcass components were affected by bST treatment.…”

“…There was no difference in spleen weight between treatment and control groups. Godfredson et al (1990) also reported that, growth hormone treatment did not change spleen weight in lambs.…”

“…In a similar study Beerman et al (1990) found that kidney weights were 13% greater in lambs treated with oST (P<0.05). On the other hand, Godfredson et al (1990) reported that GRF-A did not change kidney weights. In the present study, bST treatment did not change filled or empty gastrointestinal tract weights.…”

Growth hormone response to long-term GH-RH administration in lambs

“…Other authors (5,13) have described similar findings. The animals in our study and those used by them were in the active growth period in which the somatotrophic axis seems to be maximally stimulated (15) and thus difficult to be modified by exogenous GHRH.…”

“…On the contrary, continuous GHRH infusion using slow release pellets or osmotic minipumps did not modify circulating GH levels. These data differed from those reported by other authors (13) in which an elevation in plasma GH levels after continuous GHRH administration was described. The infusion of a more potent GHRH analog than ours in GODFRED-SON's studies could explain their results.…”