GROWTH-HORMONE AND INSULIN-LIKE GROWTH-FACTORS IN POULTRY GROWTH - REQUIRED, OPTIMAL, OR INEFFECTIVE

With a continually expanding market for poultry meat products, increased production demands of as much as 50% by the Year 2000 have been predicted. Indications already exist that this magnitude of expansion is not likely to be met by increased production output and genetic selection alone, and that other methods of improving growth performance per bird via exogenous manipulation of the growth process are needed. Studies in mammalian species clearly demonstrate the importance of growth hormone (GH) and its potential for enhancing productivity in domestic mammals. However, the role of GH in growth of poultry appears to be much more complex. Taken collectively, studies to date indicate that significant, positive effects of GH on growth performance of normal, growing poultry are possible. Expression of such effects appear to be largely contingent on the period of posthatch development (late posthatch being more responsive than early), and the pattern of several key metabolic regulatory hormones resulting in response to GH. Such regulatory hormone responses are largely influenced by the pattern or magnitude of exposure (acute versus chronic) to GH in birds. At this time, the available information on the potential for insulin-like growth factors to enhance growth is limited, and further studies are needed before a definitive role for these peptides in growth and development of poultry can be assigned.