The effect of in ovo growth hormone administration at eighteen days of embryogenesis on posthatch broiler growth and immune response

Abstract

The purpose of the following studies was to determine the effects of in ovo manipulation of growth hormone (GH) at eighteen days of embryogenesis on the posthatch growth of broilers as well as selected parameters of immune function. Broiler body weights were increased during the first 3 wk of life following albumenous 18 day embryonic administration of either recombinant bovine GH, recombinant porcine GH or thyrotropin-releasing hormone. However, these growth improvements did not persist beyond 3 wk of age in either sex and neither hatchability nor sex ratio were altered . Increasing total dietary protein, methionine and lysine levels of the starter diet 20% above National Research Council recommendations had no consistent impact on 18 day in ovo GH-related growth of male or female broilers. Subsequently, more moderate increases in dietary protein (22% starter, 22% grower) were found to increase 18 day ovine GH (oGH) -treated female, but not male, body weights at 4, 6 and 8 wk. When neonatal B-lymphocytes were exposed to 2.0 []g/ml oGH in vitro, enhanced mitogen stimulated proliferation (DNA synthesis) was observed in 2 trials. Furthermore, neonatal B-lymphocytes obtained from chicks treated at 11 days of incubation with albumenous oGH (25 []g) injection, were observed to exhibit an enhanced proliferative response to in vitro mitogen stimulation in 2 trials. Separation of cells by sex indicated that this response occurred primarily in female chicks. The final study investigated the possible effects of injection site on the in ovo administration of GH. Dye injections indicated that amnionic injections were possible and subsequently it was determined that amnionic injections increased the bioavailability of GH administered in ovo at 18 days of embryonation. The results of these investigations provide evidence that albumenous in ovo GH administration at 18 days of embryogenesis does not provide an effective means for improving post-hatch growth of broiler chicks and suggest that alternative injection methodologies may improve the bioavailability of GH administered at this time. While a positive GH-related effect on B-lymphocyte proliferation was observed, the possibility of enhanced immune function and vaccine response remains to be evaluated.