Feeding birds in the context of an antibiotics ban brings challenges, but also opportunities. Nutrition is about more than offering nutrients to meet requirements for maximum performance. Nutrition’s role goes beyond this to embrace raw materials, feed additives selection and ideal bacterial ecology. All this supports top digestion and absorption, along with balanced microflora, and an adequate immune response. Ensuring an optimal function of the gastrointestinal system is vital to successful egg production.

People are aware of food safety issues due to high profile food scandals linked to animal production. Nowadays, the public, government regulatory agencies and the animal food industry are working to fulfil expectations for the production of quality, safe products. The shift towards less antibiotic use worldwide brings new opportunities for improving gut health through nutrition to promote health in the egg industry.

In order to express an animal’s genetic potential, the digestive tract must support an optimal digestion and absorption of nutrients, minimising gastrointestinal illness, stabilising and/or positively modulating the microbial ecology, and enabling the bird to mount an effective immune response. Opportunities to optimise gut health of the pullets and layers, preventing pathogenic insults that may directly or indirectly affect performance are often overlooked.

Gut health challenges in egg production

In the rearing house, birds are exposed to continuous stressors (vaccination programs, beak trimming, medical treatment, etc.) this results in feed intake depression. In addition, the focus is on flock uniformity, body weight and sexual maturity at the expected age. The gut development (physiologically and immunologically) and the microbial ecosystem are often not considered. In some cases, birds are systematically treated with antibiotics in their first five days of arrival, when their digestive tract is still in an immature state, and microbiome establishment is an up-hill struggle.

The challenges inherent in egg production, combined with physiological stress due to hormonal changes, make it difficult to accomplish optimal feed utilisation and maximum production while maintaining egg quality. Moreover, the reality is that many flocks in production suffer a lack of uniformity, bacterial enteritis, necrotic enteritis (NE), dysbiosis (microbial imbalance) and focal duodenal necrotic. Later in the production cycle, further challenges are faced with a leaky gut and reduction in villi length associated with reduction of nutrient absorption, mainly minerals. As a result, increased cracked eggs, micro cracks and dirty eggs are seen, plus a reduction of total eggs.

Coccidiosis was ranked as the most important threat during rearing, regardless of the housing system (cage or non-cage), according to a survey conducted in 2014 by the Association of Veterinarians of Egg Production in USA. It also highlighted colibacilosis as the main issue in cage-housed layers. The survey’s participants indicated that gastrointestinal problems are responsible of 50 percent of health issues of the flock when birds are in production and 40 percent when they are growing. Other health problems also mentioned were viral diseases related to the respiratory system. It’s important not to overlook the fact that such challenges may drive secondary bacterial diseases, leading to performance losses.

If the gut function is impacted by pathogens, there is not only an immunological response but also a change in passage rate, digestion, mucin secretion, and an increase in turnover rates of the intestinal epithelium. As a result of reduced feed intake, there is a higher maintenance nutritional requirement, as nutrients are diverted to bolster the immune system. Energy and nutrients expended to mount a strong enough immune response to defeat disease, as a consequence of a disturbed microbial ecosystem, reduce absorption and digestion of nutrients - increasing Feed Conversion Rate (FCR) - overstimulating the immune system. As a consequence they trigger enteritis and noticeable performance losses.

Laying hens can maximise feed utilisation efficiency for egg production, when a healthy gut is developed. A healthy gut can be defined as ‘a steady state where the microbiome and the intestinal tract exist in symbiotic equilibrium and where the welfare and performance of the animal is not constrained by intestinal dysfunction’. Not only is the gut the major organ for nutrient digestion and absorption, it also works as the first protective mechanism to exogenous pathogens which can colonise and/or enter the host cell tissues. The gut is the largest immunological organ in the body, therefore a more robust gut should make for a healthier animal which can optimise nutrients better.

Managing gut health through nutrition

Crude fibre has been regarded as an inert nutrient in monogastric animals. However, this is not the case, as it can have roles in improving gut health, enhancing nutrient digestion and modulating behaviour. A minimum constraint should be established, for instance five per cent in diets for laying hens. Besides the fibre content in the diet, there are benefits to the digestive system of birds when coarse particles are fed. Flocks fed with larger particles will develop larger and more muscular gizzards and longer intestinal tracts. Coarser feed particles require more time in the gizzard to be ground into smaller particles, before they can enter into small intestine. Increased retention time stimulates pH drop, which has a bacteriocidal effect. Larger feed particles have a longer transit time through the gut, which improves the length of microvilli and increases the absorptive surface area in the intestine, and thereby positively affects digestibility and nutrient absorption.

Layers have a preference for larger particles, and the preference becomes stronger with age. Therefore, hen behaviour also improves, not only due to birds having to spend more time eating, but also because they have less time for vices such as feather pecking / cannibalism. Feeds containing high levels of powdery raw materials should be avoided. Birds find it more difficult to consume fine grist; and, once consumed, there is a direct outflow through the gizzard without utilisation. Hence a feed of larger grit size is desirable. An addition of two per cent oil also assists in achieving a homogenous feed with optimal particle distribution.

Dietary ‘protein’ has significant effect on the gut health

The primary role of amino acids from feed for animals is for growth and development of organs and tissues, mainly to serve as building blocks in protein synthesis. However, amino acids are also essential in many metabolic pathways to regulate physiological functions and modulate response in the body’s immune system; mucin, epithelial cells, antibodies, enzymes, hormones, etc.

Nonetheless, a proportion of amino acids and non-amino acid nitrogen offered through the feed is not well processed in the digestive tract, generating substrates for microbes and toxins for the animal. This material can thus insult the ileum, causing overgrowth of pathogenic bacteria, imbalance in the gut ecosystem, gut irritation, dysbacteriosis and in some cases subclinical necrotic enteritis. Large and insoluble protein particles which are not assimilated by the animal, go to the large intestine, leaving the digestive system through the faeces. However, small/soluble protein particles pass through the ileocecal junction into the cecum, where their breakdown (putrefaction) takes place and ammonia, amines, indoles and branched chain fatty acids are produced. These compounds can be toxic and problematic.

Excess of ‘protein’ not only increases production costs, it also generates health problems in the bird. However, reduction of crude protein (total nitrogen) in feed must be accompanied by the balancing of the amino acid profile and supply according to the requirements of the birds. Precise (amino acids) nutrition implies raw material (amino acid) knowledge, digestibility, awareness of poor processing of protein sources, and the use available pure amino acids. This approach can then meet the demand of maintenance, health challenges and egg production without excess of nitrogen. The correct balance of digestible amino acids – also called: ‘Ideal Amino Acid Profile’ – is shown Table 1.

Table 1. Recommendations for standardiaed ileal digestible amino acids for laying hens. AMINOHen®, % of diet & daily amino acid intake/mg

	Lys	Met	Met+Cys	Thr	Trp	Arg	Ile	Val
Ratio to Lys	100	50	91	70	21	104	80	88
Intake, mg/d dig AA	831	415	756	582	174	864	665	731

*Digestible amino acid demand for laying hens and optimal contents in feed (100g) daily feed intake.

Supporting the above, Drew, MD et al. 2004 studied the effects of dietary protein source and level on intestinal populations of Clostridium perfringens in broiler chickens. Two studies demonstrated that the level of dietary crude protein (230 and 400 g/kg) and protein source (soy protein concentrate or low-temperature-dried fishmeal) of diets affect the growth of C. perfringens populations in the lower intestinal of the broiler chicken.

A significant interaction between protein source and level was observed where the number of C. perfringens present in the ileum and cecum increased as the level of crude protein in the diets increased in the birds fed fishmeal-based diets, (P < 0.05) but not in the birds fed soy protein concentrate based diets. This suggests that the level of crude protein, protein source, and amino acid content of diets might all be predisposing factors to outbreaks of clinical necrotic enteritis.