Influencing gut populations to promote better health, reduce the use of antibiotics and improve performance has arguably become as important as bird genetics in recent years.
Getting nutrition right – whether that’s by formulating diets to support bacteria considered beneficial, or using additives to suppress bacterial populations considered harmful – can make the world of difference.
We outline some key trends and strategies from experts, offering farmers insights into the research currently under way.
Good gut health: Laying the foundations
Conditions in the early days of the modern commercial broiler’s life means the development of its microbiome is vastly different to that of its jungle fowl ancestor.
In most species, the pioneer microbiome is maternally derived, with transfer of bacteria taking place during birth and at feeding. Horizontal transmission from faecal material takes place in all species in the wild.
But commercial chicks are reared to high levels of biosecurity and hygiene and have no contact with their mothers. This, combined with hatchery vaccinations, sprays or gel drops, mean their developing microbiome is very different.
Chicks may acquire a “humanised” microbiome from hatchery workers, and the lack of diversity early in life leads to poor development of gut and mucosal immunity, which may be a contribution to poor gut health and infection susceptibility.
Areas to focus on for enhanced gut health
- Immunosuppressive diseases (IBD, PCVAD)
- Vaccination and health of breeders
- Robust neonate/optimal immunity
- Nutritionally optimal diets
- Enhanced management practice
- Greater data recording and analysis (water and feed intake, temperature)
- Feed and water quality and consistency, including additives
Paul Wigley, professor of avian infection and immunity at Liverpool University, says that as a result, common members of the microbiome (Escherichia coli, Enterococcus spp) are often causes of early mortality in broilers.
Prof Wigley adds that, while enhanced genetics through breeds such as the Ross 308 or Cobb had some effect on the microbiome, it was less significant than the external environment.
And while technology has allowed science to find hundreds of novel bacterial genomes from the chicken caecum, it is likely we have only covered about 20% of the taxa in the caeca.
Antimicrobials have played a key role as therapeutics, prophylactic drugs and growth promoters, but increased antibiotics stewardship in the EU means there is a need for alternatives, including pathogen control against NE, colibaccillosis and food-borne pathogens.
Competitive exclusion products – which occupy a physical niche preventing colonisation, produce metabolites that inhibit other species and stimulate immunity – can play a role and seem most effective when linked to closely related organisms, such as between salmonella serovars.
But neither they nor probiotics are really effective when dealing with campylobacter – the most common cause of food-borne bacterial gastroenteritis (more than 500,000 cases a year), with 60-70% of retail chicken still campylobacter positive despite the efforts to reduce it.
Prof Wigley says a more “nuclear” effective option against Campylobacter jejuni might be a faecal or caeca transplant approach, which could reduce pathogen carriage by exclusion, improve immune development or even do both.
In tests, transplant material has been harvested from “clean” eight-week-old broiler chickens, diluted and snap-frozen. Material has then been fed to chicks within four hours of hatch.
Results of five batches of tests have shown that this transplant method can reduce Campylobacter jejuni by cutting shedding rates, as it changes the number and type of bugs in the microbiome of the bird.
Facts about poultry microbiomes
- Made up of about 500 bacterial taxa
- A big range of protobacteria and archaebacterial species
- Hugely variable
- Differs between intestinal compartments – caecum and ilium very different
- Ceaca have the greatest numbers (c10CFU/g).
- Excess amounts of gamma-proteobacteria (enterobacteriacae) can be associated with poor gut health
- Can be modulated to improve health and/or productivity.
The effect of going antibiotics free
More than half of US broilers were raised without antibiotics last year and the trend, particularly in developed nations, is for an ongoing decline in use in the years ahead.
Antibiotic growth promoters (AGPs) have been associated with increases in certain bacterial families in the gut, such as lachmospiraceae, genera (including faecalibacterium) or species (some lactobacilli). But perhaps the most consistent effects seem to be enhanced epithelial structure and function, aiding nutrient digestibility.
AGPs have effected modification of the gut microbiota, but data investigating their effects on gut immune parameters – such as cell populations, cytokines and chemokines – are more limited.
Leon Broom, head of the Gut Health Consultancy, Exeter, says there is evidence the reduction of AGPs is leading to an increasing incidence of intestinal diseases, such as coccidiosis and necrotic enteritis.
As a result, it is important to understand the key factors affecting the microbiome, including age, diet, breed, biosecurity, hygiene, housing and drugs given to birds. Research published this year show how microbiota changes over time as the maternal influence wanes and the environmental influence takes over.
There is a huge amount of diversity in broilers in the first 12 days and this continues to rise until day 20, when the gut stabilises.
Prior to slaughter, there is evidence of gut diversity beginning to decline. Scientists have been trying to work out which bacteria are positive (lachnospiraceae, erysipelotrichaccae) and which are negative (gammaproteobacteria, faecalibacterium) and which have both positive and negative effects (clostridium, lactobacillus).
Immune development in broilers at birth was based on low numbers of herterophils and macrophages and immature T- and B-cells. Between week one and two, mature heterophil and B-cell numbers increased and by week four, the endogenous intestinal IgA had rapidly increased and the bird displayed more mature immune responses.
Dr Broom said various studies have reported that greater inflammatory responses are associated with better diseases resistance and also improved growth performance.
Three key goals for sustainable poultrymeat production
The interplay between a lower carbon footprint, increasing demand for slower-growing birds and a continued need to reduce antimicrobial use is important to consider.
1. Carbon-neutral targets
Carsten Pedersen, owner of Livestock Feeding Consultancy, says one of the largest issues facing the poultry industry is the challenge to become carbon neutral.
Dr Pedersen says the broiler sector is becoming more efficient, pointing out Aviagen’s decision to raise the bar for entry to its Ross Club, which recognises the top broiler growers in the UK.
From July, the Ross Club 400 became the Ross Club 420, with the qualifying entry level raised to a European performance efficiency factor (EPEF) of 420 and above.
Feed conversion rates in the poultry sector are among the best in the agricultural industry. Modern broilers weigh about 2.5kg at 39 days, with a liveweight feed conversion ratio of about 1.6kg of bodyweight gain, compared with about 2.9kg of feed a kilogramme gained in the pig sector and 6.8kg in the beef industry.
Dr Pederson says feed additives already play a role in lowering the environmental effects of animal performance by reducing the amount of non-digestible nutrients, but there is the potential to do more. “The industry needs much more education and knowledge transfer for the farmer so they know how to use them.”
2. Slower-growing birds
A challenge facing the sector is the drive by animal welfare groups to press for slower-growing birds, which Dr Pedersen says has far greater environmental implications (see “Daily liveweight gain by breed”).
“Genetics play a major role in animal performance. Consumers have a choice to make,” he says.
Daily liveweight gain by breed
Ross 308 – 65g/day
Ranger Classic – 50g/day
Rambler Ranger – 35g/day
3. Antibiotics use
On the subject of antimicrobials, poultry vet Daniel Parker, from Slate Hall Veterinary Practice, warns that after years of declining antibiotics use in the sector, figures covering 2018 will show a rise in use.
The causes are unclear, but could be due to the fact that 2018 was one of the hottest summers on record and heat stress can cause disease that requires antibiotics treatment.
Mr Parker says the UK poultry industry would not be going down the “no antibiotics ever” route, common in some US companies.
Broiler production issues
There are three key areas where antibiotics are being used:
1. Chick quality (43% of antibiotics)
Yolk sac infection
Early septicaemia – E coli, enterococcus, pseudomonas
2. Leg health (47%)
Femoral head necrosis
Purulent arthritis (the main issue this year)
3. Enteric issues (10%)
One of the major benefits to the health and welfare of the industry has come from the introduction of the Renewable Heat Incentive, which has prompted producers to switch from oil and gas heaters to woodchip burners.
This has reduced moisture content in sheds, led to better litter quality, reduced coccidiosis and enhanced gut health: “It’s all simple stuff, but has made a tremendous difference.”
Other areas where farmers perhaps need to do more is around drinking water hygiene, ensuring that biofilm is removed through high-pressure flushing and use of ultrasonics and in temperature control: “Farmers need to ensure that chicks don’t get too hot, either in the hatchery, during transport or in sheds.”
All the experts were talking at the recent Gut Health Symposium