The biggest challenges facing the poultry industry today include disease prevention, particularly in the absence of antibiotics, and optimum nutrition, especially with regards to being able to incorporate novel/local ingredients into the diet. Interestingly these two are linked as much of the disease pressure that challenges current poultry production is enteric in its nature. Since the presence or absence of specific nutrients/antinutrients in the diet will influence the structure of the microbiome, it is clear that the diet has a role to play in the susceptibility of the animal to enteric and perhaps even systemic disease.
Feed enzymes play a role in moderating nutrient flow to the lower intestine by two mechanisms. The first is that they simply improve the digestibility of nutrients at the ileal level and as a result, there is less substrate remaining for the microbiota resident in the large intestine. A well-digested diet restricts nutrient supply to the large intestine which generally is considered beneficial if the goal is to minimise the risk of rapid increases in microbial populations. This is particularly true with regards to minimising the flow of undigested nitrogen into the large intestine as this not only provides the nutrients needed for many potential pathogens, but putrefaction of protein also yields undesirable amines, indoles, skatole and many other products which are damaging to the structure of the intestine. Thus the use of enzymes which improve the digestibility of amino acids should play a key role in the future nutrition of poultry. It is important to note, however, that the value of such products is maximised only when the matrices for each amino acid is employed and thus the total protein content of the diet reduced. In this way, performance of the animal is maintained, ie the digestible amino acid content of the diet is maintained, but with a diet which is lower in protein. By definition, such a strategy will reduce the flow of nitrogen into the large intestine and thus reduce the risk of a putrefactive fermentation. Almost all feed enzyme in use today, phytases, NSPases and proteases, can play a role in this regard, with phytases probably being the most under-utilised in terms of application of the benefits they bring in dietary formulations.
The second mechanism relates to the first but is likely specific to NSP’ases. Most species of bacteria that can putrefy proteins can ferment carbohydrates, and if both are available the preference is for the latter. If there are equal quantities of both, then the fermentable carbohydrate will quickly be consumed such that in the more distal regions of the intestine there will be proportionately more fermentable proteins. NSP’ases produce soluble fragments or oligo-saccharides from their action on cereal and oilseed meal cell wall material which are prebiotic in their nature. This means they are fermentable by the intestinal microbiota but neither digestible nor absorbed by the host animal. Since NSP’ases continue to work on the cell wall material in the digesta with passage through the small intestine, they continuously produce fermentable carbohydrates which replenish that consumed and ideally maintains an optimal fermentable carbohydrate: protein ratio. In this role, it is important that the NSP’ase is dosed sufficiently such that the optimum rate of oligomer production is achieved. Excessive dosage may be detrimental with some NSP’ases. Some enzymes may “over-process” the oligomers to simple sugars which are absorbed by the animal and are often excreted in the urine, causing litter moisture problems. Thus correct dosage is essential if such benefits are to be realised. In most commercial situations the recognition of the importance of correct dosage for phytases is real and apparent, whereas with NSP’ases, checking in feed activity regularly is not considered important. As we move forward into an era with fewer and fewer anti-microbial products, such a view will have to change.
Feed enzymes are by no means a panacea, but they should play a role in future antibiotic-free programmes along with other nutritional and managerial interventions.
Presented at the XXV Latin American Poultry Congress in Guadalajara, Mexico.