Optimising enzyme utilisation in poultry diets

It is generally accepted that chickens fed wheat or rye are less responsive to enzyme treatment compared to those fed other conventional feed ingredients. Photo: Peter Roek

Enzyme supplementation in poultry nutrition allows flexibility in diet formulation, enhances performance and litter quality, improves poultry health, and reduces total production costs. How chickens respond to enzyme treatment, however, may vary depending on one or more of the factors listed below.

When developing an enzyme system that can effectively improve chicken performance under different feeding, management and environmental conditions, the use of enzyme supplements should be based on a thorough understanding of multiple factors to achieve optimum results.

It is generally accepted that chickens fed wheat or rye are less responsive to enzyme treatment compared to those fed other conventional feed ingredients. This is due to the presence of appreciable amounts of non-starch polysaccharides, such as pentosans in wheat and rye, which are held responsible for the reduction in nutrient digestibility and performance in chickens.

It is assumed that an increase in viscosity is the primary mechanism by which these water-soluble non-starch polysaccharides reduce the response to enzyme treatment. An increase in the viscosity of digesta may limit the mixing of nutrients and impair the diffusion of enzymes within the intestinal contents, resulting in poor digestibility. The viscous character of non-starch polysaccharides in wheat and rye is also responsible for the excessive stimulation of intestinal microbial activity, which means that more nutrients are fermented instead of being enzymatically hydrolysed, thereby masking the enzyme effect on the dietary protein and other nutrients.

Feed processing

Overheating of feeds, (i.e., above 80°C) during pelleting or expanding, also increases the subsequent intestinal viscosity. Viscosity will influence the scale of the response observed with the addition of enzymes and hence reduce nutrient digestibility and feed efficiency due to the linear relationship between these parameters and viscosity (R²=0.94). The effects of overheating on enzyme activity may vary, however, depending on the origin of the enzyme, i.e. bacterial enzymes, such as transglycosylases, transpeptidases, carboxypeptidases and endopeptidases, are more resistant to heat than those derived from fungi, such as proteases, amylases, cellulases and lipases. In all cases, overheating during feed processing should be avoided, especially with heat-sensitive enzymes, for better results.

Enzyme form

In a study comparing liquid and dry forms of enzyme supplements, no differences were noted in terms of the body weight of broiler chickens at 35 days of age when both forms of the enzymes were given in similar concentrations. The response of chickens to liquid enzymes may be enhanced only at higher doses. When liquid enzymes were applied at 1ml/litre, the birds exhibited increased growth (1,677 g) compared to the group given an enzyme level of 0.5 ml/litre (1,627 g) at similar feed intakes. In this case, however, the cost-benefit ratio should be taken into account.

Further studies on enzyme forms have shown that coating dry enzymes can reduce the efficacy of the product compared to an uncoated version. This was attributed to the delayed release of the enzymes from the coated product in the digestive tract, thereby affecting their instant role in nutrient utilisation.

Timing of enzyme application

In one study, the application of enzymes during the period from 1-21 days of age yielded stronger effects than their use during 22-37 days of age (Table 1). This may be because the gastro-intestinal tract is in development and has a limited capacity to handle the digestion process through endogenous enzyme secretion during the first three weeks of age. There is also a slower rate of passage of feed through the gastro-intestinal tract during the early stages of life which later increases due to the increased feed intake as the bird grows older, thereby reducing the response to exogenous enzyme treatment as the bird grows older.

Frequency of enzyme application

How chickens respond to enzymes may also vary depending on the frequency of enzyme application. It was found that the intermittent use of enzymes (i.e., the use of enzymes for 1 day followed by a day off) significantly increased chicken performance in terms of dry matter digestibility, weight gain, feed efficiency and production index compared with continuous enzyme application, particularly during the first three weeks of age (Table 2). This was probably due to the positive feedback mechanism of exogenous enzymes on gastro-intestinal enzyme secretion under the intermittent application system. The latter system can thus replace continuous enzyme applications at all ages while saving over 60% on the cost, although further research is needed on the cost-saving aspect.

Artificial premixes vs natural enzyme sources

A study was conducted to compare the performance of broiler chickens fed diets supplemented with either artificial enzyme premixes or dried fig meal. Growth rate and feed efficiency increased by 7% and 12%, respectively, when the dried figs were fed over the artificial sources. No information, however, is available on the effect of using dried figs in diets fed to laying hens. The cost of a dried fig diet varies from one part of the world to another but, in all cases, is less than one containing the commercial enzyme preparations.

Stocking density

High stocking density affects the microbial profile of the litter, particularly where the litter material is not sufficiently dry and friable. In one study, the mould count (10⁵) increased from 0.6 to 1.3 in the litter at stocking rates of 10 and 17 chickens/m², respectively. Upon inhalation of a greater amount of toxins produced by mouldy litter, this would reduce the activities of lipase, amylase, trypsin and chymotrypsin enzymes in the gastro-intestinal tract which leads to insufficient digestion and absorption of protein, fat and carbohydrates, all of which are needed to perform various biological functions. An adequate supply of these enzymes, therefore, should be considered in this case to achieve better utilisation of feed nutrients and hence improve bird performance. This should, of course, be coupled with other known management plans that help to maintain high-quality litter in chicken houses.

Effects of heat stress

Heat stress is a major source of systemic oxidative stress since it causes an imbalance between the production and accumulation of oxygen-reactive species in cells and tissues and the ability of a biological system to detoxify these reactive products. Oxidative stress affects growth performance and the meat quality of broilers and promotes inflammation of the ovaries in layers, thereby leading to impaired laying performance. Antioxidant enzymes such as superoxide dismutase, catalase and glutathione peroxidase enzymes represent the primary defence system involved in protecting cells from the damaging effects of oxidative stress, as they work by de-activating free radicals before they attack cellular components. Commercial preparations containing enzymes other than these types may not be equally effective in combating oxidative stress.