Animals undergoing a challenge to their state of health mount a vigorous response which involves both the innate and acquired immune systems. The varied non-specific responses of an animal to infection, inflammation or trauma are collectively referred to as the acute phase response (APR). The APR is a very complex reaction involving both local and systemic effects. Acute-phase proteins (APP) are a group of blood proteins primarily synthesised in the liver in response to pro-inflammatory cytokines being released primarily from leukocyte activation during an APR. The use of APP for diagnostic purposes in both human and veterinary medicine has increased greatly within the last decade.
The aim of this thesis was to investigate the APR in chickens in response to i) vaccination using a Newcastle disease and Infectious Bronchitis (N/B) Live, freeze-dried virus vaccine; ii) an experimental challenge with Poultry red Mite (PRM); (iii) an LPS challenge experiment with an E. coli LPS. Four APP namely serum amyloid A (SAA), alpha 1 acid glycoproteins (AGP), ovotransferrin (OVT) and ceruloplasmin (CP) were studied in detail along with other blood component including heterophile / lymphocyte (H/L) ratios and corticosterone. For SAA, AGP and CP, species specific ELISA kits are now commercially available, but these had not previously been validated. The results from chapter 2 demonstrated that all three ELISAs gave good accuracy, had a suitably low detection limit and allowed discrimination between different levels of APP in chicken samples. For OVT a lab based radial immunodiffusion assay (RID) was used.
The results of the current study have shown that a mild response of APP (SAA and AGP) in SPF chick post vaccination at day one and two post vaccination. H/L ratios also increased, and this measure was deemed more sensitive and consistent in terms of measuring the mild stress response under the conditions employed than the APP though of these the SAA was the most promising.
In the other experimental challenge with PRM in laying hens, the serum levels of SAA were also significantly increased, and this was subsequently found to be positively correlated with the level of PRM infestation which was monitored for several months, further serum protein profile alterations were described in this study. Whereas, LPS challenge induced significant with high magnitude of APP (SAA, AGP and OVT). In addition, local expression of APP has been investigated and significant changes of other blood components were described. Looking for the APR by non-invasive way in chickens challenged with LPS, there were interesting sensitive detection of the body surface temperature. Also, a significant correlation of the cloacal with the body surface temperature changes in development of pyrexia.
In summary, the research presented in this thesis has demonstrated that SAA is the most sensitive APP and therefore potentially the most useful biomarker in chickens (layers and broilers): this APP increased more rapidly and by a greater magnitude than the other APP following a range of stimuli. AGP and OVT moderately increased and usually peaked later than SAA, while CP rarely changed.
Further research is needed to investigate the relationship between the local and systemic APR and to determine the significance of extrahepatic versus hepatic production of APP in the chicken and, the associated H/L ratio and thermal imaging in early disease recognition as both of these measurements proved to be useful in such studies
