Do Cationic Antimicrobial Peptides (CAMPs) impact on the microbiota & consequent gut health of commercially important broilers?'

The poultry industry aims to produce healthy birds that survive and grow in all environments in which poultry are managed. However, recent regulations limiting the use of antibiotics in livestock means that birds raised in commercial settings are often severely compromised through the environmental challenges associated with intensive production regimes. This often leads to reduced growth performance, disease & increased bird mortality. As well as the resultant economic impact, such losses raise important issues & concerns regarding bird welfare. Research is thus pivotal to understand and exploit, through breeding, the natural defences of commercially important bird lines. Such research will help to keep birds healthy, reduce bird losses arising through disease, and maintain a safe & secure, national & international, food source. Birds and mammals have natural defence mechanisms that function from hatch or birth and quickly destroy any microbes that would normally kill them. A group of effectors of this innate system are small positively charged molecules called antimicrobial peptides (AMPs), which are synthesised constitutively or induced, and display broad spectrum activity against bacteria, fungi and viruses. In the chicken there are 13 of these peptides which are called Avian beta-Defensins (AvBDs), and these are synthesised by a plethora of body surfaces including those of the gastrointestinal (GI) tract. At the GI tract or gut surface they exist in very high concentrations and kill pathogenic microbes trying to cross the gut barrier & invade the body. However there is a suggestion that at more dilute concentrations, as exist in the gut lumen, they allow the selective growth of commensal bacteria that help to inhibit the growth of potential pathogens & as such help to maintain a healthy gut. In collaboration with a leading poultry breeding company we have found that the expression of gut AvBDs in two pedigree bird lines is line specific, indicative of a genetic influence, displays regional variation and importantly is responsive to the environmental conditions in which the birds are maintained. These data therefore suggest that the gut AMP response of birds is important in protecting birds from disease and, importantly, can probably be manipulated through selective breeding programmes as well as environmental factors. This project will, in collaboration with an international poultry breeding company, extrapolate our research to include commercial lines derived from the pedigree stocks. We will apply a range of molecular & cellular techniques to determine & compare the GI AvBD profiles of four lines reared from hatch to 21 days in either high hygiene or low hygiene conditions, and investigate whether the AvBD patterns are (1) specific to each bird line, (2) responsive to the living conditions of the birds (3) correlated with specific groups of indigenous microbiota, & (4) associated with good or poor gut health and disease resistance. Scientifically these data will allow GI factors associated with the gut microbiota, gut health & disease resistance to be established. Such factors may be used as genetic selection tools to improve disease resistance in commercially important lines of poultry & exploited through selective breeding programmes.

Preliminary data indicates that Avian beta-Defensin (AvBD) gene expression in the gut epithelia of two commercial elite pedigree bird lines is specific to a particular bird line, displays regional variation, but is responsive to the environmental conditions in which the birds are maintained. A key question is whether the commercial bird lines derived from the pedigree stocks and central to a successful and bio-secure poultry industry also exhibit such characteristics and, if so, whether such properties are similarly affected by environment, and impact on bird gut health & welfare in general. Our objective is to define the roles of cationic antimicrobial peptides, CAMPs, specifically AvBDs, in bird gut health & disease resistance. To achieve this we will in collaboration with Aviagen Ltd, set up a trial in which four of the company's commercial bird lines, selected for balanced breeding goals, are raised in either a pedigree environment (high hygiene) or a sib-testing environment (low hygiene) and sampled at 0, 7 ,14 & 21 days of age respectively. Using molecular (qRT-PCR) and cellular (immunohistochemistry) techniques we will investigate & compare regional patterns of AvBD gene expression in the GI epithelia of the commercial bird lines and determine the influence of bird genetics (SNPs) & rearing environment on such patterns. We will through 16SrDNA profiling & LC MS/MS analyses of gut scrapes & samples establish whether patterns of AvBD expression impact on the gut microbiota and are associated with a specific cationic proteome. Scientifically these molecular, genetic, proteomic & microbiota data, in conjunction with gut immunohistochemistry, will allow the roles of the AvBDs and other GI factors in bird gut health & disease resistance to be established. Commercially such information may be used to improve disease resistance in broiler lines & exploited through selective breeding programmes.

Strategically this research proposal fits within the Animal health and Global Security research priorities of BBSRC. The research is a collaborative project with Aviagen Ltd, a world leading poultry breeder & supplier. It is intended long term that the knowledge arising from the project will be used by Company R&D for future genetic selection & breeding programmes to improve disease resistance in their commercial livestock. This will, in due course, have economic and social impacts for the Company as well as the UK economy per se. In turn national & international poultry businesses who are customers of the Company and rearing birds for use in the food industry will benefit economically from the more disease resistant livestock. This will be achieved through a reduction in bird wastage concomitant with the reduced susceptibility of the birds to disease. In addition the research will impact on the consumer ie society, who will benefit from a safer, more secure food supply but without either nutritional compromise or a cost premium. Globally, the improved disease resistance in intensively produced domestic poultry will help to reduce the threat of diseases, with their origin in poultry, transferring to humans. This reduction in infection risk has potential impact both with respect to national & international economies and public health. The project will interrogate potential relationships between CAMPs, part of the innate immune system, and the bird gut microbiota. Identification of CAMP/microbial patterns or interactions signals the possibility of selecting for specific gut microbial populations by stimulation of innate defences through environmental factors &/or diet. In relation to the latter it is feasible that nutritionists & immunologists, through the selection of specific microbial populations, could design and test nutritional programmes that manipulate gut innate immunity & improve disease resistance. Underpinned by the science this concept has significant impact not only in relation to livestock production but also arguably in relation to diet & well being of human populations including young & ageing populations.