In egg production, health of the layer gut matters more than ever. That’s because new housing systems are presenting new health risks, notes Dr. Elijah Kiarie, assistant professor and McIntosh Family Professorship in Poultry Nutrition in the department of Animal Biosciences at the University of Guelph in Guelph, Ont.. In short, contact with more litter makes chickens more prone to the proliferation of gut pathogens.
Layers still housed in conventional cages (and all commercial layers in Canada were housed in these cages until recently) are separated from litter, and therefore do not generally require the use of antibiotics to promote health and growth. Nowadays, hens are being transitioned into new housing systems (mostly free-run or enriched colony cage) where they can scratch and dust bathe, exposing them to higher excreta dust levels and higher ammonia levels as well. Hens in free-run housing are at particular risk as they are direct contact with litter all the time on the barn floor. While manure belts are used in some free-run barns, their effectiveness can vary.
Regarding health issues in layers that require treatment with antibiotics, it’s very important to prevent these, as the withdrawal period for antibiotics in layers is very long. This is due to the length of time involved in egg formation and the fact that egg yolks are very efficient at accumulating antibiotics.
Indeed, if a disease issue occurs in a large percentage of a particular flock, it is often best economically to cull the entire flock. For their part, since meat birds raised in antibiotic-free programs inherently experience more disease challenge, it’s important to investigate strategies for suppressing pathogens and maintaining intestinal integrity, such as feeding probiotics, immune-nutrients (yeast) and organic acids.
Kiarie is currently leading a group of scientists and graduate students studying various aspects of poultry gut health in two areas: layers/pullets (Ilona Parenteau, Zipporah Mwaniki, Alisha Wornath-Van Humbeck, and Neijat Mohamed) and broilers/turkeys (Haley Leung, Emily Kim, Aizwarya Thanabalan and Mohsen Mohammadigheisar).
Kiarie notes that whether it’s layers or broilers/turkeys, gut health is a matter of a long-term generational view. Because developmental events related to immune system competence start during chick embryo development and continue after hatching for several weeks, a focus on maternal, embryonic and early post-hatch nutrition strategies is needed.
“Our research revolves around three concepts/themes that we believe are vital for maintaining a functional and healthy gut in poultry,” Kiarie explains. “Specific products and ideas may slightly differ for meat (broilers/turkey) and layers, but the approach is similar.” Here is a round up of their progress within these three themes.
Optimal gut function
Poultry require a certain amount of diet structure for the gut to properly develop and function. However, the composition and processing of modern low-fibre commercial poultry diets is focused on improving feed intake and efficiency, not on gut health, Kiarie notes.
Ironically, however, better feed efficiency can be achieved indirectly through providing diets with moderate amount of fibre. “With some fibre, you get a longer retention time in the gizzard, leading to more exposure of feed particles to gastric juices,” Kiarie explains. “This improves digestion and nutrient absorption and, therefore, better feed efficiency. We have found that today’s laying hens could adjust their gut physiology to handle more fibrous feed.”
Research is now focused on characterizing the impact of introducing higher-fibre diets to pullets and the subsequent effect of that layer productivity, longevity and more.
In addition, Kiarie’s team is studying how feed enzymes are best used to decrease the amount of undigested nutrients (such as protein and phosphorous) in the gut. Undigested nutrients can lead to higher numbers of pathogens in the gut and other negative health impacts. Kiarie notes the most common feed ingredients in the modern poultry diet (corn, wheat and soybean meal) can vary in nutritional value, and that diets with lower nutritional value result in more undigested nutrients.
Feed enzymes are one factor affecting the balance of good and bad microbes in the gut. Enzymes increase nutrient digestibility, but also result in the production of prebiotic materials in the gut that good bacteria can feed on. “The peculiarity with prebiotics is that they promote production of short chain fatty acids, which are known to have a microbiota stabilizing effect and one of these fatty acids, butyrate, has been shown to stimulate bird gut defenses against Clostridia species, Salmonella and E. coli,” Kiarie notes.
“It is time for the industry to embrace the role of feed enzymes not only in increasing feed digestibility but in how they transform feed metabolism. Our future research will systematically investigate combinations of enzymes with probiotics, as we believe they have both distinct and complimentary mode of action.”
High protein diets are another area of concern relating to microbial population balance. Birds eating these diets have increased concentration of bacteria such as Clostridia in the gut, and their excretions give off more ammonia as well. There is controversy over how low crude protein in layer diets can go, Kiarie notes, and “because their use can reduce egg production, size and so on, we are investigating supplementing these diets with various synthetic amino acids on hen performance and gut health.”
Kiarie and his colleagues are also currently investigating the potential of insect meal (Black soldier fly larvae meal) to replace soybean meal and amino acids in layer diets. A least cost formulation indicates that 20 per cent insect meal in an 18 per cent crude protein layer diet could replace all soybean meal, but the nutritive and functional value of insect meal must be fully characterized.
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Gut development and integrity
Kiarie notes that there are numerous substances known to enhance gut development that could be strategically applied in starter diets. Epidermal growth factors (EGF) are one example. They are a critical component of mammalian colostrum and milk.
Kiarie’s team recently provided EGF to broiler chicks challenged with Eimeria (which causes coccidiosis) to assess its ability to stimulate chick gut growth and function and how this affects growth performance. They observed that an increasing dose of EGF improved weight gain five days after hatching, and also improved the expression of genes related to gut health.
Nucleotides, the building blocks of DNA/RNA molecules involved in many functions at the cellular level, are another example. Chickens are capable of synthesizing adequate nucleotides, but production in young chicks and birds with gut health challenges can be impaired. The scientists did a similar trial to EGF and found birds fed nucleotides had higher intestinal villi height (the bumps that add more surface area to the intestine, and therefore better nutrient absorption), higher body weight gain and a trend for improved feed conversion.
Conclusions, implications and further research
Kiarie concludes that proper nutrition is unachievable without a healthy and functional gut. “Good gut health requires an intact gut, strong immunity and balanced microbe populations,” he notes. “Nutrition can no longer be considered to be just a calculation of nutrients but a synthesis of all elements provided by the feeds, nutrients, anti-nutrients, functional factors and implications on gut health and function. We believe the ability to find and evolve the next generation of feed additives will be driven by, among other factors, understanding the mechanisms of action and the implications on animal health and performance.”
Furthermore, Kiarie says the way most feed additives are evaluated is too simplistic and focuses on their individual effects, but poultry often receive diets containing a mix of additives where some can influence the effects of others. His team is, therefore, investigating possible combined effects and potential synergies.
“We also have to factor in differences in the physiological maturity of the gastrointestinal tract and determine if there is value in providing additives early in life for long-term health and performance,” Kiarie says. “These approaches will lead to a more consistent and profitable outcome in the use of additives.”
Kiarie and his colleagues believe three concepts are vital for poultry gut health: optimal gut function; microbial balance; and gut development and integrity. Specifically, they have found:
- Better feed efficiency can be achieved indirectly through providing higher amounts of fibre
- Feed enzymes could play a larger role in decreasing undigested nutrients; they also result in the production of prebiotic materials that good bacteria feed on.
- Research is needed into how low crude protein diets can be supplemented with synthetic amino acids.
- Insect meal may replace soybean meal and amino acids in layer diets someday, but more research is needed.
- Numerous substances known to enhance gut development could be strategically applied in starter diets.
- Feed additives should be evaluated in a more complex and synergistic way.