Proper nutrition is one of the management practices that can provide an optimal approach to improved gut health, performance, and profitability of the poultry business.
Broiler diets high in wheat or barley maize may increase the incidence of necrotic enteritis in comparison to corn-based diets. These cereal grains contain high levels of indigestible water-soluble non-starch polysaccharides (NSP). The ingestion of high levels of soluble NSP leads to increased digesta viscosity and decreased digesta passage rate and nutrient digestibility, thereby increasing the chances of rapid bacterial colonisation. A highly viscous intestinal environment will increase the proliferation of facultative anaerobes like gram-positive cocci and enterobacteria and in turn, create an environment that can support obligate anaerobes such as C. perfringens.
Animal protein ingredients such as fishmeal or meat and bone meal are often associated with an increased risk of necrotic enteritis, especially when fed in excessive amounts. This is probably due to the higher levels of methionine and glycine in fishmeal compared to most plant protein sources. Methionine and glycine have long been known to stimulate the growth and establishment of microflora such as C. perfringens and other pathogens in the gut. It is important to note that the inclusion of an increased level of fishmeal alone is no guarantee for the proliferation of C. perfringens. That is, the effects of a protein source are less pronounced with a corn-based diet as opposed to wheat-based or barley-based diets. It is, therefore, impossible here to connect a single dietary compound with the overall changes in the microflora.
Dietary fat affects immune competence either by altering the cell membrane structure or by modulating the synthesis of prostaglandins, which play an important regulatory part in many biological processes including the immune response.
In one study, the resistance of chickens to disease agents such as Escherichia coli and Mycobacterium tuberculosis was linearly enhanced as the level of lard or safflower oil was increased from 3% to 9%. Mortality associated with such diseases was also reduced with elevated levels of fat in the diet. Rancid fats and oils should be rejected since they facilitate the persistence of intestinal pathogens and the likelihood of intestinal inflammation.
Proper fat storage conditions should be evaluated frequently to control rancidity development. The addition of antioxidants and mycotoxin binders to feed can reduce the rancidity effects.
In one study, the addition of rice husk as a fibre source has promoted the growth of beneficial Lactobacillus bacteria which prevents mucosa infections and hence contributes to the process of digestion and absorption. There was also increased production of short-chain fatty acids (SCFA) due to the addition of fibre sources to the diet. The production of SCFA in the cecum increased from only 22 mg/g to 51 mg/g with fibre feeding. This was linked with a bacteriostatic effect on some enteric bacteria such as C. perfringens and Escherichia coli thereby improving the health and performance of birds.
The rate of inclusion of fibre depends largely on the particle size of feed, i.e. 7.5 g/kg with a particle size of 1-2 mm and 15 g/kg of feed with a particle size below 1 mm.
Coccidiosis, an enteric disease of major economic importance worldwide, is caused by Eimeria spp specialised in invading and replicating in the intestine. The disease causes losses in production and high morbidity ranging from bloody enteritis, with high mortality, to being subclinical and silent but affecting feed intake and efficiency.
To counter these complicated effects, there are nutritional strategies including formulation of key amino acids, vitamins, short and medium-chain fatty acids, prebiotics, and enzymes, among others, that can be utilised to reduce the infection, alleviate the signs, and boost the compensatory growth after infection.
Herbal plants that might be used in poultry feeding include the spiny acanthus (Acanthus spinosus), ginger (Zingiber officinale), and the Indian Curcuma (Curcuma longa). Studies have shown that such species of plants act as natural antibiotics against coccidiosis and other microbial diseases. They could, therefore, be used in place of synthetic antibiotics which in many cases reduce body vitamin B and vitamin K due to their effect on the gut micro-flora synthesising the vitamins, in addition to their high costs relative to the natural plants.
Green tea leaves (Camellia sinensis) have also been used in the field of therapeutic nutrition, mainly because of the presence of polyphenol derivatives such as carnitine and catechin, which play an important role in fatty acid oxidation and the production of ATP. The said derivatives also play an important role in the prophylaxis and/or treatment of neuropathic diseases, striate opacity, pancreatitis, fibroid tumours, etc. These effects, however, have so far been observed with laboratory animals only, and further work is needed to ascertain the potential role of tea leaves in the therapeutic nutrition of poultry.
Pelleting maintains the normal structure and function of the gastrointestinal tract. The gizzards of birds fed pelleted diets were better developed compared with other birds whose gizzards were atrophied when fed ground diets since they had no hard particles to grind down.
The well-developed gizzard can be regarded as a barrier in preventing pathogenic bacteria from entering the distal GIT. In pellet-fed birds, there is also an increased concentration of VFA and reduced pH. The reduced pH has an antimicrobial effect on pathogenic bacteria entering the distal part of GIT.
In one study, there was a reduction of Salmonella in the caeca associated with decreasing caecal pH and increasing amounts of VFA with a reduction in the numbers of caecal Enterobacteriaceae in broilers during growth.
Acidifying drinking water for poultry with sodium bisulphate for the first 7 days of life provides a second layer of protection to the lactic acid-producing bacteria (LAPBs) that are part of the crop’s normal ecology. This helps the newly hatched bird to maintain a low crop pH until it has established its population of stable LAPBs. A low crop pH also reduces the number of Salmonella, Clostridium, or other harmful microflora that pass farther along the digestive tract and enables the bird to colonise with normal gut flora.
References are available from the author upon request.