New insights into the mechanism and actions of growth hormone (GH) in poultry

Despite well documented anabolic effects of GH in mammals, a clear demonstration of such responses in domestic poultry is lacking. Recently, comprehensive dose-response studies of GH have been conducted in broilers during late post-hatch development (8 to 9 weeks of age). GH reduced feed intake (FI) and body weight gain in a dose-dependent manner, whereas birds pair-fed to the level of voluntary Fl of GH-infused birds did not differ from controls. The reduction in voluntary FI may involve centrally mediated mechanisms, as hypothalamic neuropeptide Y protein and mRNA were reduced with GH, coincident with the maximal depression in Fl. Growth of breast muscle was also reduced in a dose-dependent manner. Circulating IGF-I was not enhanced by GH, despite evidence that early events in the GH signaling pathway were intact. A GH dose-dependent increase in circulatings 3,3',5-triiodothyronine(T3) paralleled decreases in hepatic 5D-III monodeiodinase activity, whereas 5'D-I activity was not altered. This confirms that a marked hyperthyroid response to GH occurs in late posthatch chickens, resulting from a decrease in the degradative pathway of T3 metabolism. This secondary hyperthyroidism would account for the decreased skeletal muscle mass (52) and lack of enhanced IGF-I (53) in GH-treated birds. Based upon these studies, it is now evident that GH does in fact have significant effects in poultry, but metabolic responses may confound the anabolic potential of the hormone. (C) 1999 Elsevier Science Inc. All rights reserved.status: publishe

Altered chicken thyroid hormone metabolism with chronic GH enhancement in vivo: consequences for skeletal muscle growth

In contrast to most vertebrates, GH reportedly has no effect upon somatic growth of the chicken. However, previous studies employed only one to two dosages of the hormone, and limited evidence exists of a hyperthyroid response that may confound its anabolic potential. This study evaluated the effects of 0, 10, 50, 100 and 200 mug/kg body weight per day chicken GH (cGH) (0-200 GH) infused i.v. for 7 days in a pulsatile pattern to immature. growing broiler chickens (9-10 birds/dosage). Comprehensive profiles of thyroid hormone metabolism and measures of somatic growth were obtained.status: publishe

The effect of glycerol inclusion on broiler performance and nutrient digestibility

International audience1. Crude glycerol from biodiesel production was offered ad libitum to broiler chickens in a 21-d feeding and digestibility trial. The study was designed as a 3*2+1 factorial design with 3 levels (33, 67, 100 g/kg) of glycerol from 2 sources, A and B (PRS Environmental Ltd and John Thompson and Sons Ltd) and a control diet. The diets were formulated to contain apparent metabolisable energy (AME) 12.95 MJ/kg (assuming 14.6 MJ/kg for glycerol). 2. No significant interactions occurred therefore only the main effects were discussed. At 7-14 d feed conversion ratio (FCR) showed a significant linear response with increased glycerol inclusion (P<0.05). However quadratic responses on FCR were observed for the 21-28 d period and 7-28 d. 3. Glycerol digestibility was significantly greater with birds offered the 67 g/kg and 100 g/kg glycerol-based diets (P<0.001) in contrast to the digestibility of 33 g/kg glycerol-based diets. 4. Glycerol inclusion level also had an effect on AME, which increased linearly with increasing glycerol inclusion (P<0.05). Birds offered the diets containing glycerol also required less energy per unit gain in contrast to birds offered the control diet (P<0.05). 5. When examining the effect of source of glycerol, source A glycerol, resulted in the highest AME (15.20 vs. 14.72 MJ/kg P<0.05). There was no significant effect of glycerol source on the other performance parameters. 6. Glycerol digestibility was significantly greater with glycerol from source B (John Thompson and Sons Ltd) with a mean value of 0.848 (P<0.004) in contrast to source A (PRS Environmental) glycerol digestibility being somewhat less with a mean value of 0.757. 7. In conclusion, glycerol source did not affect performance and increasing level of glycerol improved FCR with 67 g/kg inclusion resulting in the most efficient conversion of feed to gain without any negative effects upon nutrient digestibility