To achieve improvements in feed efficiency, mineral utilization or uptake, more than 85% of the phytate should be eliminated from the diet.

By CASEY BRADLEY, CARRIE WALK and CRAIG WYATT*

*Casey Bradley is a technical manager, Carrie Walk is a research manager and Craig Wyatt is a technical manager at AB Vista.

PHYTATE (e.g., IP6) is a significant anti-nutrient that binds other key nutrients important for growth, including calcium, zinc and iron, plus other trace minerals and amino acids.

Dietary phytate can increase maintenance costs and reduce energy utilization for growth. The combination of the anti-nutrient effects associated with phytate reduces animal performance. Therefore, aiming for near-complete dietary phytate destruction would be advantageous when it comes to improving gain and feed efficacy while targeting a lower cost of production.

Research has shown that, depending on the phytase source, up to 65% of phytate-phosphorus typically is released with a standard dose of phytase — 500 phytase units (FTU) per kilogram of feed — with the resultant production of lower phytate esters — IP5, IP4, IP3, IP2 and IP1 — as well as free inositol. These lower phytate esters (IP2-4) can accumulate in high levels compared to an untreated diet. They are also considered as anti-nutrients, binding to minerals such as calcium, zinc, iron and copper and interfering with pepsin activity.

Super-dosing phytase

Recent research shows that feeding a super-dose level (more than 1,500 FTU/kg) of an enhanced Escherichia coli phytase breaks down proportionately more phytate and lower phytate esters producing inositol in the gizzard of broilers (Figure 1) and the stomach of pigs. Inositol production is positively correlated with improvements in bodyweight gain and feed conversion ratio.

In addition, super-dosing phytase has been shown to increase zinc and magnesium digestibility and, subsequently, increase tibia zinc and magnesium concentrations as well as improve iron absorption in the animal, as measured by hemoglobin levels.

Specific phytase characteristics are required to ensure that maximum phytate destruction is achieved within the conditions of the gastrointestinal tract. There are currently a number of phytases on the market, each differing in its ability to hydrolyze phytate and the lower esters. There is no one unique property responsible for better performance in vivo; rather, a combination of characteristics is critical to achieving a consistent response in phytate destruction and feed efficiency.

Intrinsic thermostability

Phytases must survive the rigor of feed processing to be active and efficient at phytate breakdown in the animal. Thermostability can be achieved though intrinsic thermostability or by coating technology.

Intrinsically thermostable phytases can be used in feed without coating protection to ensure rapid action on phytate and highly efficient phytate hydrolysis, which can be further achieved through the use of super-doses of phytase.

Coating technologies can delay dissolution and, therefore, reduce the efficacy of the product, reducing phosphorus release and bone ash (Figure 2).

When applying at super-dosing levels for performance gains, it is important to destroy phytate and higher phytate esters quickly before they have the opportunity to exhibit negative anti-nutritional effects. Hence, anything that impedes dissolution of the phytase into solution, such as coating, will hinder this process and reduce performance.

Gastric pH, pepsin

A narrow window of opportunity exists within the gastrointestinal tract where phytate is soluble and more easily hydrolyzed. Phytases must deliver high and consistent activity for optimal phytate degradation at gastric pH (2.5-3.5), and most bacterial phytases have a high relative activity in this pH range.

In order to achieve this consistent activity, the phytase must also be resistant to pepsin hydrolysis at this pH. In vitro work indicates that the activity of third-generation phytases following a pepsin challenge can vary from a low of 66% to a high of 92%, with the enhanced E. coli phytase having the highest residual activity.

Fast action

A key characteristic influencing animal performance is the ability of a phytase to maintain high activity at low phytate concentrations to completely destroy phytate and the lower esters.

The phytase must work quickly and have a high affinity toward phytate and the lower phytate esters to ensure that, even in diets with low substrate levels, the enzyme works with full efficacy to release nutrients that would otherwise be unavailable.

Second, the phytase must work quickly to release phosphorus and other nutrients that will then limit the anti-nutritional effect of phytate at super-dosing levels, delivering improvements in feed conversion ratio and a return on investment.

The beneficial effect of reducing the lower esters can be seen in recent animal research on the enhanced E. coli, with super-dosing at 1,500 FTU/kg reducing IP4 and IP3 concentrations by 32% and 85%, respectively. These lower esters are detrimental in terms of their effect on nutrient utilization.

The Table illustrates the significant relationship (correlation) between the IP4 or IP3 concentration in the ileum and the negative effect IP4 and IP3 have on energy, protein and mineral utilization, as indicated by the negative correlations. This means that as the concentration of IP4 or IP3 in the ileum increases, the energy, protein or mineral digestibility decreases. Therefore, further phytate destruction to phytate esters below IP3 may explain part of the improved performance when super-dosing with an enhanced E. coli phytase.

Optimum characteristics

To achieve improved feed efficiency, mineral utilization or uptake, more than 85% of the phytate should be eliminated. Not all commercially available phytases are capable of quickly and effectively eliminating phytate and lower phytate esters due to the different characteristics they possesses.

For example, a typical corn/soybean meal-based diet contains approximately 1% phytate, and each phytate molecule contains six phosphates. To achieve 85% phytate destruction with super-dosing, this is equivalent to a 0.21% available phosphorus release value from phytase. If only one phosphate is removed from each phytate molecule, that would yield only 0.04% available phosphorus (or 16% phytate hydrolysis). Therefore, to achieve 0.21% available phosphorus or 85% phytate destruction, hydrolysis of both phytate and lower phytate esters is required.

Based on previously published standard curves (Figure 3), it can be shown that an enhanced E. coli phytase can achieve this destruction at approximately 1,500 FTU/kg, while other phytases are limited in their ability to deliver this level of phytate breakdown, even at higher dose rates.

The difference between a 0.21% available phosphorus/super-dosing application and a 0.15% available phosphorus/standard release is indicative of the phytase's ability to break down phytate at very low concentrations, as well as the lower esters (IP4, IP3 and IP2). It is this ability to target phytate and lower ester breakdown with a phytase at super-dosing levels that delivers better performance and a return on investment for producers.

Volume:88 Issue:01