Stress activates a number of endocrine pathways that alter an animal's physiology in a manner which can result in undesirable meat quality. Animals frequently exhibit meat quality defects, including ecchymosis, at slaughter due to the stress of slaughter. This thesis explores how stress related hormones interact with adrenergic receptors to alter muscle and vascular physiology. Fallow deer were exposed to either a transciptional regulator (hydrocortisone), a beta adrenergic recptor agonist (clenbuterol) or a beta adrenergic receptor antagonist (propranolol). The administration of hydrocortisone resulted in a negative feed-back type reduction in circulating cortisol. Animals treated with propranolol and clenbuterol displayed less severe eccymosis. These results indicated that the beta 2 adrenergic receptor (B2AR) is important in controlling ecchymosis severity. B2AR was also found to be important in mediating vascular dynamics, growth and energy pathways. To investigate how adrenergic receptors alter skeletal muscle gene expression and meat quality, an in vivo wistar rat model was developed in conjunction with in vitro muscle cell (L6) experiments. Gene expression of B2AR, its associated kinase (BARK) and collagen type III, prolyl- 4-hydroxylase (P4Hy) was measured in rat muscle and L6 cells. Following exposure to clenbuterol and hydrocortisone, growth and meat quality were determined. The L6 experiments revealed that gene expression following exposure to hydrocortisone and B2AR ligands paralleled the in vivo rat changes in B2AR, BARK, collagen type III, and P4Hy gene expression. In both L6 and wistar rat models the B2AR and BARK genes are similarly expressed following clenbuterol exposure. Both rats and deer exposed to clenbuterol had significant increases in growth rate and a reduction of intramuscular fat. The B2AR therefore appears to be a major mediator of many interrelated events including energy distribution, growth and vascular response to stress. Habituating animals to stress stimuli may increase their coping ability and improve welfare and meat quality. / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:ADTP/182343 |
| Date | January 1998 |
| Creators | Grogan, Shawn Patrick, University of Western Sydney, Hawkesbury, Faculty of Environmental Management and Agriculture, School of Agriculture and Rural Development |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Source | THESIS_FEMA_ARD_Grogan_S.xml |
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