The overall goals of our research program are to improve the efficiency by which soft tissue growth occurs in domestic poultry, and the quality of the final products derived from these tissues, which constitute muscle foods for human consumption. In order to achieve these goals, we maintain multiple research efforts. These include (1) a basic research program focused on understanding what endocrine and metabolic factors are involved in the regulation of muscle and adipose tissue growth, including thyroid and pancreatic hormones and, in particular, the growth hormone (GH)/insulin-like growth factor I (IGF-I) axis. Our immediate studies are directed at the mechanism by which the GH is communicated to target cells to generate a response, and focus on the GH receptor, soluble GH binding proteins (GHBPs), and GH signal transduction components such as JAK2. In addition to investigating these endocrine and metabolic factors in normal growth, we collaborate in the use of models of abnormal growth, which help to provide even further insights into these processes. These include the pathological model of growth retardation found in spiking mortality (stunting/runting) syndrome in broilers, in which the GH/IGF-I axis and pancreatic hormone reserves are markedly deranged, as well as the genetic model of the sex-linked dwarf chicken, in which target tissue receptors for GH are defective, resulting in retardation of skeletal and lean tissue growth. Growth and metabolism-related disorders in commercial poultry production situations underline the need to understand the regulation of both normal and abnormal growth and metabolic processes in birds, in order to effectively manage growth-related and metabolic problems and reduce mortality, as well as improve the efficiency of poultry meat production.
We also maintain (2) a more applied program of research whose goal is to improve the efficiency of production, and the quality of poultry meat. This program includes development of preslaughter technologies to reduce carcass contamination in meat birds, and studies to establish the relationship between GH and voluntary feed intake in broilers.
- PTYSC 407, Comparative Physiology of Domestic Animals
- PHSIO 572, Animal Physiology
Research Support Associate
- Jill Hadley
- Melissa Costell: Ontogeny of the thyrotropic and somatotropic responses to GH during late postnatal development
Efforts will focus on establishing a dynamic, hepatocyte perifusion culture system to study ( in vitro ) the role of GH patterns on GH signal transduction, and to establish the ability to measure changes in GH signal transduction components in this system. This will involve very labor-intensive procedures that must be developed from the "ground up."
Studies were conducted to investigate the role of thyroid hormones in regulation of GH receptor (GH-R) and tissue IGF-1 production in the absence of GH action. Endocrinologically, the sex-linked dwarf chicken is hypothyroid, hypersomatotropic, and during early posthatch growth, has markedly reduced circulating IGF-1 concentrations compared to normal. Through collaborative studies, it has been determined that a significant level of IGF-1 production is GH-independent and tissue specific in the chicken, and that FG action may modify the effect of other regulatory hormones on IGF-1 production, which is a unique finding.
A considerable number of collaborative studies have been completed with the investigatories at Georgia Poultry Laboratory on spiking mortality syndrome (SMS) in broilers. It has been demonstrated (and over the past year has generated a significant data base to the effect) that pancreatic glucagon levels are severly depleted, in fact virtually abolished, in broilers with SMS exhibiting severe hypoglycemia. In fact tissue (pancreatic) glucagon levels were so highly correlated with plasma glucose concentrations, as to suggest the latter can be used as an indicator of pancreatic alpha cell status for field purposes.
Considerable effort has also been put into perfecting a reliable and sensitive assay for cell membrane-bound GH-R/GHBP using chemiluminescence detection. Such an assay is essential to efforts to further investigate the regulation of GHBP in the chicken.
Vasilatos-Younken, R., Y. Zhou, X. H. Wang, J. P. McMurtry, E. Decuypere, N. Buys, V. Darras, and F. Tomas. 2000. "Altered chicken thyroid hormone metabolism with chronic growth hormone (GH) enhancement in vivo : Consequences for skeletal muscle growth." J. Endocrinol. 166:609-20.
Wang, X. H., J. Day, Y. Zhou, J. Beard, and R. Vasilatos-Younken. 2000. "Evidence of a role for neuropeptide Y and monoamines in mediating the appetite suppressive effect of growth hormone." J. Endocrinol. 166:621-30.
McMurtry, J. P., C. Ashwell, R. Richards, and R. Vasilatos-Younken. 2000. "Leptin: Molecular biology and physiology in birds." In: Avian Endocrinology . A. Dawson & C. M. Chartuvedi, eds. New Dehli, India: Narosa Publishing House; pp. 1-7.
Wang, X.-H., J. R. Day, and R. Vasilatos-Younken. 2001. "Distribution of neuropeptide Y (NPY) gene expression in the chicken brain." Mol. Cell. Endocrinol. 174:129-36.
Farhat, A., C. W. Maddox, M. E. Edwards, M. H. Costell, J. A. Hadley, and R. Vasilatos-Younken. 2002. "Oral lavage with polyethylene glycol reduces microbial colonization in the gastrointestinal tract of broilers." Poultry Sci. 81:585-89.
Farhat, A., M. E. Edwards, M. H. Costell, J. A. Hadley, P. N. Walker, and R. Vasilatos-Younken. 2002. "A low residue nutritive supplement as an alternative to feed withdrawal in broilers: Efficacy of gastrointestinal tract emptying and maintenance of live weight prior to slaughter." Poultry Sci. 81:1,406-14.
Zhou, Y., X.-H. Wang, J. A. Hadley, S. J. Corey and R. Vasilatos-Younken. 2003. "Regulation of JAK2 protein expression by chronic, pulsatile GH administration in vivo : A proposed mechanism for ligand enhancement of signal transduction." J. Endocrinol. (submitted) .