New-Generation Phytase

New-Generation Phytase Benefits Poultry Performance and the Environment

New-generation phytase products will have an increasing and vital role to play in helping poultry producers to stay ahead of tightening economic pressures and environmental standards by reducing feed costs and minimizing phosphorus waste. However, to maximize the potential benefits, nutritionists must fully appreciate and account for the greater efficacy over traditional phytases when formulating poultry diets, Dr. Janet Remus, technical services manager with Danisco Animal Nutrition, told delegates attending the 3rd Mid-Atlantic Nutrition Conference in Maryland recently.

Presenting a paper entitled ‘Phytate and interaction with nutrients – considerations on the use of a matrix when applying phytase to poultry diets,’ Dr. Remus explained that increasing pressure on profit margins and tighter environmental standards regarding phosphorus provide an overwhelming case for using new-generation phytase products in poultry rations.

She emphasized the importance of knowing how much phytate is present in poultry diets when assigning non-mineral matrix values to phytase.

Phytate comprises a myoinositol ring structure to which six phosphate groups are attached, this negatively charged (anionic) structure usually being chelated with positively charged minerals (cations), proteins and/or starch. However, phosphorus bound by phytate is predominantly unavailable to poultry species, due to their lack of sufficient endogenous phytase activity to make this ‘bound’ phosphorus available. The passage of this ‘bound’ phosphate through the bird into the environment has made it the focus of environmental concerns and created a serious ‘perception’ issue for poultry producers and the wider agricultural community.

These issues aside, poultry are generally incapable of utilizing phytate phosphorus sufficiently well to support optimal growth and production without the addition of inorganic phosphorus sources such as dicalcium or monocalcium phosphate.

Feed ingredients of plant origin typically contain phytate, but although the phytate levels can alter from year to year due to variations in growing conditions, unfortunately no quick and easy method exists to measure them. This is further complicated by the fact that phytate is held in different areas of the seed across plant species. In soybeans, for example, phytate is found in conjunction with globoids (protein bodies) that are widely dispersed throughout the seed, while corn holds the majority of its phytate in the germ and most phytate in wheat is located in the aleurone.

The scientific community often describes phosphorus (P) in one of five ways:
‘Total’  – The level in the diet (or ingredient), whether bound by phytate or not.

‘Digestible’ – The difference in content between the feed P consumed and the feed P remaining undigested at the terminal ileum in poultry.

‘Available’ – Typically assessed by metabolic measurements such as weight gain and bone mineralization and expressed relative to an inorganic P source.

‘Retained’ – The difference between the level in the feed and in the excreta.

‘Nonphytate’ – The difference between total and phytate P in a raw material.

Practical nutritionists often use the terms ‘bioavailable P’ or ‘digestible P,’ the former being more common in North America and the latter widely used in Europe. 

Dr. Remus also emphasized that in addition to the different methods of describing phosphorus, not all phytases are the same. Whereas the first major phytases in commercial use were derived from different species of fungi, the latest-generation product in the North American  market, Danisco’s 6-phytase Phyzyme XP, is derived from Escherichia coli, which has demonstrated increased benefits in bone mineralization, phosphorus utilisation and bird performance.

While all phytases are capable of cleaving phosphorus off the phytate molecule given the right conditions, the performance of individual phytases in the bird varies according to a number of biochemical attributes, including pH profile, specific activity and resistance to attack by endogenous proteases. Although certain feed ingredients contain ‘native’ phytases that can cleave phosphorus from phytate, doubts remain as to their effective contribution in feed formulation. For example, phytase activity in cereals will be affected by cultivar, age of the grain, drying and storage conditions, and by pelleting temperature, so formulating diets allowing for the consistent presence of ‘native’ phytase activity alone is
impractical.

Adding phytase to the diet frees some bound phosphate and reduces the requirement for inorganic phosphorus, which is the primary method of achieving economic savings from phytase use in least-cost feed formulations. Recent research on phytases of E. coli origin has reported higher phosphate digestibility in poultry than with traditional fungal phytases, but to reduce total dietary phosphate without detriment to performance it is important to understand the content and bioavailability of phosphorus in various raw material sources, as well as the phosphorus needs of the animal. In broilers, which are selected for rapid growth, the issue is particularly pertinent and raises a question over how well estimates of phosphorus requirement produced even 10 years ago reflect current genetic lines. In addition, most nutritionists agree that there has been some ‘over-formulation’ of phosphorus in diets due to concerns over the birds’ needs under commercial conditions.

Because phytate chelates certain minerals, the use of phytase has been shown to increase the availability of cationic minerals such as calcium, zinc, copper, cobalt, iron, magnesium, nickel and manganese.  This offers further benefits from the use of phytase, particularly as the excretion of some of these minerals have a negative impact on the environment.

Belief among animal nutritionists in applying matrix values to amino acids and protein when using phytase has been debatable, but the general trends emerging in the scientific literature are that phytase improves amino acid availability, albeit to varying degrees. For example, in recent studies the use of rice bran to increase the phytate level in a corn soy diet decreased the apparent ileal digestibility of lysine, methionine, threonine, leucine, valine, tryptophan and isoleucine, which was reversed by the addition of an E. coli phytase (Phyzyme XP).

As the addition of phytate has been shown to decrease the availability of wheat starch by 60 per cent, it has been proposed that phytate may directly interact with starch, or the protein closely associated with the starch granules. Phytate may also reduce the activity of endogenous amylase, although this relationship could depend on the level of calcium in the diet, as this enzyme requires calcium for its activity. Phytase has been shown to increase diet AME with addition of up to 750 FTU/kg, while in recent studies the addition of an E. coli-origin phytase to corn/soy diets, using rice bran to vary the phytate level, found that phytase increased diet AME by up to 0.39 MJ/kg (93 kcal/kg) on a dry matter basis.
While the improvements in the availability of key amino acids and energy with phytase are relatively small, they can nevertheless have a significant economic impact in feed formulation. Some believe, however, that set matrix values inadequately reflect the anti-nutritional impact of phytate across different ages of poultry under different dietary conditions. It is anticipated that higher phosphate bio-efficacies for the new generation E. coli phytase should also translate to higher amino acid and AME matrix values than for traditional phytases.

Of the three phytases in the U.S. market, only one phytase supplier has published matrix values for nutrients other than calcium and phosphorus for poultry species. As our understanding of the consequences of phytate origin and level and the dynamics of its interactions with phytase in the gut develops, so nutritionists will assign matrix values to amino acids and energy with greater confidence. In the future, under certain situations, it may even be more appropriate to relate phytase use to dietary levels of phytate rather than simply remove a set quantity of inorganic phosphorus. In addition, because phytate is associated with cell wall fibre (NSP) in some ingredients, phytase and NSP enzymes may provide some synergistic effects.

To commercial nutritionists, Dr. Remus offered the following advice:
•    Determine ‘typical’ dietary phytate levels, as this can influence the matrix values that may be assigned to non-mineral nutrients and the optimal phytase inclusion level.

•    Assign appropriate inclusion levels to the phytase product or premix in formulation and ensure matrix values are correct for the inclusion level of phytase.

•    Determine the phosphorus content of key sources (and the variation therein – particularly in the case of ingredients such as meat and bone) and select sources with high biological values and minimal variation. In the case of inorganic sources, periodically review/adjust the phosphorus availability/digestibility values in line with published information.

•    Ensure you are familiar with your supplier’s recommendations concerning the use of their phytase product.

•    Periodically evaluate feed for added phytase activity level. It is important to recognise that enzymes are temperature sensitive to varying degrees and under practical conditions milling/pelleting temperatures and steam pressure affect in-feed enzyme activity when using dry products. Liquid application systems should also be checked periodically for both in-feed absolute recovery of phytase from pelleted feed and for coefficient of variation.

Summarizing, Dr. Remus emphasized that although the use of phytase in feed is currently linked to the level of inorganic phosphate, in that the use of phytase requires a certain quantity of inorganic phosphorus to be removed, this approach fails to consider the underlying content of phytate in the diet. Adjusting the level of phytase relative to phytate could therefore prove to be a more viable approach in the future. Ultimately, said Dr. Remus, phytate level and therefore the potential for phosphorus excretion must be considered to enable an economically optimal quantity of phytase to be added and more accurately impact the level of phosphorus released into the environment. 

Danisco Animal Nutrition is a division of Danisco A/S (Denmark).