The Properties of Recombinant Chicken Growth Hormone and Its Effects on Growth, Body Composition, Feed Efficiency, and Other Factors in Broiler Chickens

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Abstract
Recombinant chicken GH (rcGH) was produced and characterized. Comparison of protein sequence, amino acid composition, mol wt, purity, and immunocross-reactivity showed that except for the N-terminal methionyl group arising from the bacterial expression system, the recombinant and pituitary-derived cGHs were identical. When tested in a hypophysectomized rat growth assay, the recombinant and pituitary materials had the same specific bioactivity. Within 60 min after sc injection of rcGH (480-960 .mu.g/kg) in chickens, plasma GH levels increased 4- to 6-fold and remained significantly elevated for at least 5 h. Thrice-daily injections from age 2-24 days had little effect on growth or feed consumption in either male or female broiler chicks. Plasma levels of insulin and triglycerides were significantly elevated by rcGH in 24-day-old females, but not in males. Injection of rcGH counteracted a reduction of tibia length observed in saline-injected controls. The rcGH had no effect on carcass protein, ash content, or nitrogen retention. It is important to note that exogenous GH can be a productivity-enhancing factor in other commercially important species. Administration of bovine GH to cows has been shown to induce a significant increase in milk production (28). This study shows that administration of rcGH to chickens can lead to some significant metabolic effects. However, it is the conclusion of this report that the level of circulating GH is not the limiting factor in the growth of this highly selected species.