|Practice tip||Peer reviewed|
Cite as: Jacela JY, DeRouchey JM, Tokach MD, et al. Feed additives for swine: Fact sheets – high dietary levels of copper and zinc for young pigs, and phytase.J Swine Health Prod. 2010;18(2):87–91.
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Phytase is an enzyme that increases availability of phosphorus in pig diets.
Phytase lowers the amount of supplemental phosphorus required in the diet.
Because of improved dietary phosphorus utilization, less phosphorus is excreted in the manure.
Phytase is susceptible to degradation during extended storage periods.
Pigs need dietary phosphorus for normal body maintenance and growth. It is an essential element that is required in many physiological processes in the pig’s body and thus sufficient amounts must be included in the diet. This element is abundant in most grains found in swine diets. However, only a small amount of phosphorus is utilized from grains, because the majority of the phosphorus exists in a form (phytate) that is not digestible in swine. The digestibility of phytate phosphorus can be increased when supplemental phytase is included in the diet.
What is phytate?
Phytate or phytic acid is the main storage form of phosphorus in grains and oil seeds. Pigs are unable to digest phytate, as they lack digestive enzymes that break it down. As a result, a substantial amount of phosphorus is excreted as waste, with only 14% of the total phosphorus bioavailable in corn and up to approximately 50% in wheat.1,2 Because phosphorus is an essential element, inorganic phosphorus, which is highly available, is typically supplemented in the diet to meet the pig’s requirement. Phytate also has other antinutritive effects, as it is known to reduce the availability and utilization of other nutrients.3-5
Phytase is an enzyme that specifically acts on phytate, breaking it down to release phosphorus in a form available to the animal. This greatly reduces the need for supplemental inorganic phosphorus and improves the nutritional value of feedstuffs. Phytase activity is expressed as phytase units or FTUs. One FTU is the activity of phytase required to liberate 1 μmol of inorganic phosphorus per minute at pH 5.5 from an excess of 15 M sodium phytate at 37°C. Unlike the nonstarch-polysaccharide-degrading enzymes, phytase is the only exogenous enzyme that has been consistently shown to be highly beneficial to pigs.6 The proven efficacy of phytase has resulted in worldwide acceptance and use in pig production.7
What is phytase derived from?
Some ingredients possess intrinsic phytase activity, which varies greatly among plant species. Corn and soybean meal contain negligible levels of phytase activity compared to wheat, which contains considerably higher levels of intrinsic phytase.8 The majority of phytase activity in cereal grains is found in the aleurone layers.9 However, this may be lost when ingredients are subjected to high temperatures, such as during the pelleting process.10 Commercially available exogenous phytases are commonly derived from either fungi or bacteria, such as Aspergillus niger and Escherichia coli,6 but can also be expressed in yeasts.11,12
How much phytase should be added to pig diets?
The amount of phytase needed in a diet depends on the dietary ingredients used and enzyme activity for the product to be used. However, it is important to note that differences in laboratory assays exist, as well as differences among company products, ie, 1 FTU of one product may not be equivalent to 1 FTU of the other. It is important to obtain from the supplier the actual amount of phosphorus release based on their claimed enzyme activity for accurate diet formulation. In general, manufacturers’ recommended levels of commercially available phytases can replace inorganic phosphorus levels by 0.12% in pig diets. As the amount of phytase added to a diet increases, the release of phosphorus from phytate also increases in a curvilinear fashion.13 This means that phosphorus release diminishes with each additional unit of phytase until additional dietary levels of phytase fail to result in a further response.
What affects the efficacy of phytase?
Several factors can influence the efficacy of phytase, including the amount of phytate in the diet, the amount of phytase added to the diet, and the type of phytase. Studies have shown greater responses to phytase in pigs fed diets that contain higher amounts of phytate.6 Phytase derived from E coli bacteria is also more efficacious than the fungal phytases in terms of the amount of phosphorus released per unit of phytase, according to published data.14-16 However, analytical techniques being used to determine phosphorus release vary among commercial phytase manufacturers. Because of this, the amount of phosphorus released per unit of phytase may differ between two phytase products, as shown in a recent study using a standard assay procedure.17 Thus, depending on the assay used, different results of phytase activity may be reported.
Because phytase is a protein, it is susceptible to denaturation when subjected to excessive heat, such as during pelleting. This may be addressed by spraying liquid phytase onto the cooled pellets to maintain the stability of the enzyme. In addition, heat-stable phytases are available. Phytase is also sensitive to degradation when stored in premixes under high temperature and moisture conditions. Hence, proper storage procedures and frequent rotation of products containing phytase must be practiced. Phytase products should be stored only in cool, dark, dry areas. The manufacturer’s recommendations should always be followed, especially when phytase is included in vitamins and trace-mineral premixes.
The calcium-to-phosphorus ratio (Ca:P) of the diet may affect the magnitude of response to phytase. Studies have shown that wider Ca:P can result in decreased absorption of phosphorus.18-20 Thus, a range of 1:1 to 1.25:1 Ca:P is recommended.
Nonphosphorus effect of phytase
In some studies in which pigs were fed diets with adequate levels of available phosphorus supplemented with phytase, improvements in growth performance were still observed,6 suggesting that phytase has a positive effect on other nutrients, eg, increased digestibility of energy and amino acids. However, results of other studies21-23 are not in agreement, thus there is no justification for assigning a nutrient value (energy or amino acid digestibility) other than phosphorus release to phytase. Phytase does improve availability of calcium and other minerals in the diet.24 It should be noted that addition of phytase also results in an overall increase in energy value of the diet. The reason for this is that more corn is added to the diet as the amount of inorganic phosphorus (which has no energy value) is reduced.
Phytase is an enzyme that increases the digestibility of phytate phosphorus, which improves the overall availability of dietary phosphorus. The use of this enzyme as a feed additive in swine diets reduces the requirement for inorganic phosphorus supplementation. As inorganic phosphorus is replaced by corn or other grains in the diet formulation, the diet’s overall energy content increases. Improved phosphorus utilization and reduced inorganic phosphorus in the diet result in less phosphorus excretion from pigs. Phytase also can increase availability of other minerals such as calcium. As phytase is sensitive to high temperature and humidity, proper storage and handling procedures should be followed to maintain the efficacy of the product. Heat stability of the product must also be considered when diets are pelleted.
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* Non-refereed reference.