Broadly speaking, four types of enzymes currently dominate the animal feed market: enzymes to break down fiber, protein, starch and phytic acid.

Fiber-degrading enzymes

One of the main limitations to digestion is the fact that monogastrics (pigs and poultry) do not produce the enzymes to digest fiber. In diets containing ingredients such as wheat, barley, rye or triticale (the main ‘viscous' cereals), a large proportion of this fiber is soluble and insoluble arabinoxylan and β-glucan. The soluble fiber can increase the viscosity of the contents of the small intestine, impeding the digestion of nutrients and thereby reducing the growth of the animal. It has also been linked with the incidence of digestive disorders such as non-specific colitis in swine, and sticky litter and hock burns in poultry.

The fiber content of wheat and barley can vary considerably according to variety, growing location, climatic conditions, etc. This in turn means that there can be considerable variability in the nutritional value of these ingredients and hence diets containing them. In breaking down the fiber, enzymes (e.g. xylanase targeting arabinoxylans, β-glucanase targeting β-glucans) can reduce this variability in nutritional value, giving rise to improvements in the performance of the feed and the consistency of the response. An added benefit is the reduced incidence of certain digestive disorders.

Protein-degrading enzymes

Various raw materials contribute to the protein content in the diet and ultimately the amino acids that fuel lean meat deposition. There is considerable variability in the quality and availability of protein from the different raw materials typically found in monogastric diets. Within the primary vegetable protein sources such as soybean meal, certain anti-nutritional factors (ANFs), such as lectins and trypsin inhibitors, can lead to damage to the absorptive surface of the gut, impairing nutrient digestion. In addition, the underdeveloped digestive system of young animals may not be able to make optimal use of the large storage proteins found in the soybean meal (glycinin and β-conglycinin).

The addition of a protease can help to neutralize the negative effects of the proteinaceous ANFs in addition to breaking down the large storage protein molecules into smaller, absorbable fractions.

Starch-degrading enzymes

To many nutritionists maize is viewed as the ‘gold standard' of raw materials. Most nutritionists do not consider maize digestion as being poor: in fact most would argue that it is better than 95% digested. However, recent evidence suggests that, at the ileal level, starch digestibility rarely exceeds 85% in broilers between 4 and 21 days of age. The addition of an amylase to animal feed can help to expose the starch more rapidly to digestion in the small intestine, and in doing so lead to improved growth rates from enhanced nutrient uptake.

At weaning, piglets often suffer a growth check because of changes in their nutrition, environment and immune status. The addition of an amylase, usually in conjunction with other enzymes, to augment the animal's endogenous enzyme production has been shown to improve nutrient digestibility and absorption and, hence, growth rate for a range of diets.

Phytic acid-degrading enzymes

Phosphorus is required for bone mineralization, immunity, fertility and growth and is an essential mineral for all animals. Swine and poultry digest only about 30–40% of the phosphorus found in feedstuffs of vegetable origin, with the remainder being tied up in a form inaccessible to the animal – phytic acid. In many instances additional phosphorus must be added to the diet to meet the animal's requirement. More than half of the phosphorus consumed from such feedstuffs is excreted in the faeces, which can result in major environmental pollution. By adding a phytase to the diet, the phytic acid is broken down, liberating more of the phosphorus for use by the animal.

The two main benefits of phytase supplementation are, firstly, the reduction in feed costs from the reduced additional supplementation of phosphorus to the diet and, secondly, environmental from reduced excretion of waste products and the threat of pollution.