Maximum Phytate Destruction25 January 2016
Phytate (IP6) is a significant anti-nutrient, binding other key nutrients important for growth including Ca, Zn, Fe, plus other trace minerals and amino acids. Dietary phytate can increase maintenance costs and reduce energy utilization for growth, writes Casey Bradley, AB Vista Technical Manager, Carrie Walk, AB Vista Research Manager and Craig Wyatt, AB Vista Technical Manager.
Phytate anti-nutrient is costing producers
The combination of the anti-nutrient effects associated with phytate reduces animal performance. Therefore, targeting near complete dietary phytate destruction would be advantageous in regards to improving gain and feed efficacy while targeting a lower cost of production.
Research has shown that, dependent on the phytase source, typically up to 65% of phytate P is released with a standard dose (500FTU/kg) of phytase with the resultant production of lower esters, IP5, IP4, IP3, IP2 and IP1 as well as free inositol. These lower esters (IP2-4) can accumulate in high levels when compared to an untreated diet and are also considered as anti-nutrients, binding to minerals, such as Ca, Zn, Fe, and Cu and interfering with pepsin activity
Superdosing phytase for phytate destruction
Recent research shows feeding a superdose level (>1500 FTU/kg) of an enhanced E.coli phytase breaks down proportionately more phytate and lower phytate esters producing inositol in the gizzard of broilers (Fig 1) and the stomach of pigs.
Inositol production is positively correlated with improvements in body weight gain and feed conversion ratio. In addition, superdosing phytase has been shown to increase Zn and Mg digestibility and subsequently increase tibia Zn and Mg concentrations as well as improve Fe absorption in the animal as measured by haemoglobin levels.
Figure 1 An enhanced E.coli phytase shows in the broiler gizzard the near complete phytate destruction, no increase in lower phytate esters (IP4 or IP3) and an increase in production of inositol (adapted from Walk et al., 2014). * below the limits of detection.
Specific phytase characteristics are required to ensure 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 their ability to hydrolyze phytate and the lower esters. There is no one unique property responsible for better performance in vivo, but rather a combination of characteristics are critical to achieve a consistent response in phytate destruction and feed efficiency.
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 superdoses of phytase. Coating technologies can delay dissolution and therefore reduce the efficacy of the product reducing P release and bone ash (Fig 2).
When applying at superdosing 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 reducing performance.
Figure 2. Effect of a coating on phytase granulates on pelleting stability (A) and toe ash (B) in broilers (Klein Holkenborg and Braun, 2001).
Gastric pH and pepsin stability
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
Ability to work quickly and at low concentrations of phytate
A key characteristic influencing animal performance is the ability of a phytase to maintain high activity at low phytate concentrations to complete destroy phytate and the lower esters.
The phytase must work quickly and have a high affinity towards phytate and 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.
Secondly, the phytase must work quickly to release P and other nutrients which will then limit the anti-nutritional effect of phytate at superdosing levels, delivering improvements in feed conversion ratio and a return on investment.
The beneficial effect of reducing the lower esters can be shown in recent animal research on the enhanced E. coli with superdosing at 1500 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.
Table 1 illustrates the significant relationship (correlation) between IP4 or IP3 concentration in 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 IP4 or IP3 concentration in the ileum increase, the energy, protein or mineral digestibility was decreased. Therefore, further phytate destruction to phytate esters below IP3 may explain part of the improved performance when superdosing with an enhanced E. coli phytase.
Table 1. Multivariate pair-wise correlations of nutrient digestibility and IP3 or IP4 concentrations in the ileum of 21-day old broilers (abstract Beeson et al., 2015).
1Multivariate pair-wise correlations; only significant correlations are presented (P < 0.05), where the R2 is > ± 0.6.
Optimum phytase characteristics, means more nutrient release per unit of activity
To achieve improved feed efficiency, mineral utilization or uptake, >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 soy-based diet contains approximately 1% phytate and each phytate molecule contains six phosphates. To achieve 85% phytate destruction with superdosing, this is equivalent to a 0.21% available P release value from phytase. If only one phosphate is removed from each phytate molecule, that would only yield 0.04% avP (or 16% phytate hydrolysis). Therefore, to achieve 0.21% available P or 85% phytate destruction, hydrolysis of both phytate and lower phytate esters is required.
Based on previously published standard curves (Fig 3), it can be shown that an enhanced E. coli phytase can achieve this destruction at ?1500 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% avP/superdosing application and a 0.15% avP standard release is indicative of the phytase’s ability to breakdown 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 superdosing levels that delivers better performance and a return on investment for producers.
Figure 3: Phosphorus release for different commercial phytases (derived from suppliers’ published data)