Feed, along with all feed ingredients, should be evaluated for quality because feed has a greater impact on gut health than any other factor. Contaminants and particle size need to be considered because these can impact gut health directly or through modulation of the bacterial population in the gut. Feed access with correct feeder spacing is crucial for the flock at all ages. But don’t forget the most important nutrient: water.
Birds rely on optimal gut health to be able to digest feed efficiently. However, the composition of the feed itself can impact gut health directly and indirectly. For example, feed contaminants such as mycotoxins can directly damage the gastrointestinal tract.
Some feed ingredients and changes in feed formulation can impact gut health indirectly by selecting and nourishing the growth of specific bacteria species in the gut. In some cases, these changes can cause the microbiota population to become unstable and lead to gut health issues.
Feed access, formulation, digestibility, quality, processing and additives are all important factors in promoting and maintaining gut health. This article considers some of the nutritional elements significant to gut health.
Access to feed and water is important for young chicks to support intestinal growth and development. Feed intake stimulates gut development (i.e., villi elongate, crypts proliferate, enzymatic activity increases, mucus is secreted, and enterocytes develop). In addition, feed intake will cause the intestines to increase in length. These developments increase the surface area available for absorbing nutrients and provide a hospitable environment for the microbiota.
Delays in access to feed and water will slow gut development and gut microbiota establishment. Since the microbiota act as a barrier to pathogenic infection, early establishment can also provide young chicks with protection from disease.
The main management objective after placing chicks on the farm is to achieve as much intake of water and feed as possible to support growth and gut health. Failure to achieve this objective will lead to irreversible problems with ﬂock performance, negatively impacting growth, feed conversion, ﬂock uniformity and gut health. When placing, ensure that chicks have easy access to feed and water. Check the chicks to ensure they are getting adequate feed and water by doing crop checks. For detailed information on chick placement and management, see Cobb’s updated Cobb Breeder Management Guide.
Access to feed and water is important not only for chick development but for the entire flock. Feed withdrawal can cause compositional changes in the microbiota, thinning of the intestines and a reduction in villi height. Unlike broilers that are fed ad libitum, broiler breeder feeding programmes are designed to manage bodyweight and promote egg production. Therefore, broiler breeders are usually fed once per day, although some producers use alternative feeding plans.
Breeders have acclimated to these feeding programmes by increasing the feed retention time in the gastrointestinal tract so the maximum amount of nutrients can be extracted from the feed. However, it is important to feed birds at the same time of the day to prevent stress and keep the microbiota population stable. It is also crucial to ensure that feeder and water space is correct based on stocking density. Incorrect feed/water space can result in gut health, production performance and animal welfare issues.
In many regions, broiler breeders are fed a diet based on corn-soybean meal. Other regions use cereals, such as wheat or barley, as alternatives to corn. Similarly, protein sources other than soybean meal can be used, including lupin, sunflower meal, canola meal or rapeseed meal. The notable differences between these ingredients are the amount and type of non-starch polysaccharides (NSPs) in these plant-based ingredients (Table 1).
Some consider NSPs as anti-nutritive because of their impact on digestive viscosity. However, these complex polysaccharides can be fermented to support a healthy microbial community and produce fatty acids that the chicken can use as an energy source. Different NSPs are selectively fermented by different bacteria, and therefore targeted enrichment of bacterial species can be accomplished by using a specific NSP.
Given the differences in NSP types in corn-soybean meal versus wheat-based diets, the question of which diet is better for gut health arises. Unfortunately, there are too many confounding variables involved to answer the question. For example, the NSPs in the digestive tract are structurally complex and interact with other nutrients and digestive components, making it difficult to determine their fates. Other factors to consider include the impact of processing on feed ingredients and variable quality (of corn or wheat).
Feed additives can be used to promote nutrient uptake (acidifiers), extend shelf-life (antioxidants) and improve digestibility (enzymes). Acidifiers in feed reduce the gastrointestinal pH, which promotes the absorption of calcium and protein and selects for beneficial bacterial species. Antioxidants can be used to prevent fat rancidity, as rancid fat in the intestine has been shown to challenge microbiota stability and select for E. coli populations. Although enzymes can be added to improve digestibility, these are used more in broiler production than in broiler breeders. Generally, we highly recommend testing any feed additive before making it part of your nutrition programme.
Feed safety is an important criterion in ingredient selection. Contaminants in feed can impact gut health by directly damaging the intestines and disrupting the microbiota. To reduce the risk of contamination, feed safety assessments with testing and auditing are prudent.
Ingredient hazards can be classified into 3 main groups: chemical, biological and physical. Chemical hazards include pesticides, heavy metals, dioxins, melamine and antibiotic residues. Pesticides are primarily monitored in grain products, whereas heavy metals are associated with mineral sources. Microbes present biological hazards that can cause health issues and include bacteria, primarily Salmonella, as well as fungi, that can produce mycotoxins. The last group – physical hazards – are contaminants such as plastic, glass or metal. Physical hazards can be detected with in-process interventions (magnets) and laboratory analyses.
It should be noted that processing raw ingredients can impact feed quality. For example, undercooking or overcooking soybeans can impact digestibility and protein availability. Depending on corn processing and storage conditions, retrograded starch can form, which is less digestible. As indicated, grains held under poor storage conditions can become mouldy, leading to mycotoxin contamination. Mycotoxins are heat stable, so once present, they cannot be removed, and producers are limited to using mycotoxin binders.
The choice of feed form (i.e., pellet, mash or crumble) depends on multiple factors, such as flock age and feed formulation. Among feed forms, particle size and uniformity are important in mash and crumble feeds but not as significant in pelleted feeds because pelleted feed is highly processed.
Particle size for mash and crumble feeds is an important consideration for age, as chicks may have difficulty digesting large particles since the gizzard and intestinal tract are not fully developed. Uniformity of particle size is also important because older birds may select larger particles and leave fine particles. Both cases can cause nutritional, gut health and overall health issues.
With respect to size, small particles provide more surface area for digestive enzymes and secretions to reach and are considered easier to digest. Conversely, large particle size is thought to stimulate gizzard development and activity, and larger particles are retained longer in the intestinal tract. A longer retention time can help release more starch in cereal grains which will facilitate bacterial fermentation. Currently, a particle size of 900 to 1100 µm is recommended for optimal digestibility.