By John Patience, Stacie Gould and Cassie Holloway, Iowa State University; Dean Koehler and Leah Gesing, VitaPlus Corp.
In many plants, such as corn and soybean meal, much of the phosphorus is stored in a compound called phytate. Why is this important? There are three reasons. First, the pig cannot digest phytate-bound phosphorus, so it passes through the pig into the manure; this is good for producing nutrient-rich fertilizer to be applied to corn and soybean fields, but not so good for feeding pigs.
Plus, if there is too much phosphorus in the manure relative to crop needs, the excess phosphorus can have adverse effects on the environment.
Second, when the phytate-bound phosphorus is poorly utilized, a phosphorus supplement, such as monocalcium phosphate or dicalcium phosphate, must be added to the diet to prevent a phosphorus deficiency; this is expensive.
Thirdly, phytate not only ties up phosphorus, but it can also make minerals and possibly amino acids less unavailable, too. So, when it comes to feeding pigs, not much good can be said about phytate.
For many years, an enzyme called phytase has been added to pig diets to help the pig utilize phytate-bound phosphorus — and it works very well. Most pig diets used in this country contain phytase if the quantity of available phosphorus in the diet is below the pig’s requirement. It is the cheapest way to help meet the pig’s requirement for phosphorus.
In most cases, sufficient phytase is added to the diet to release enough phosphorus to meet the pig’s requirement. However, more recently, people have investigated feeding much higher levels of phytase, in order to improve pig performance, presumably due to making other nutrients like minerals, amino acids or energy more available to the pig. This is referred to as super-dosing — adding levels of phytase to a diet well above that needed to meet the pig’s requirement for phosphorus.
Recent research at Iowa State University has demonstrated that super-dosing phytase in diets for pigs up to 50 pounds is beneficial, improving both rate (4%) and efficiency of gain (4%) when fed typical nursery diets. In the accompanying table, a typical nursery feeding program is identified as Treatment 1, and Treatment 2 is the same program with super-dosed phytase added. The study also looked at feeding a lower energy and lower amino acid diet, identified in the table as Treatment 3. If super-dosing phytase improves nutrient digestibility, then the response should be greater when the pigs are fed slightly deficient diets. Treatment 4 is the slightly deficient feeding program but with phytase added. In terms of growth rate, this did not turn out to be true. Unlike in the standard feeding program, there was no improvement in growth rate, but feed efficiency was improved by 3%.
Next month, we will discuss the use of super-dosing phytase in grow-finish diets.
In a related study, samples of digesta were collected from the end of the small intestine to determine to what extent super-dosing phytase destroyed the phytate molecule. As shown in the accompanying figure, the higher the level of phytase added to the diet, the greater was the reduction in phytate. At the highest level of phytase, 65% of the phytate was broken down. This is important to understand, because this could lead to improving the digestibility of other nutrients in the diet. However, the growth study does not support this, because phytase was no more effective in the nutrient-deficient diet than it was in a regular diet. It could also be that the breaking down of phytate makes it more available to the pig, which can then use it for various purposes in growth or maintenance. Because the phytate molecule has such an impact on the utilization of the diet, it is important that we learn more about it.
We concluded from these studies that adding phytase at super-dosed levels — in this case 1,130 FTU per pound — to nursery diets improves growth performance, but reducing nutrient content of the diet in anticipation of achieving a greater response is not recommended. We also concluded that one way in which super-dosed phytase may be working in the gut of the pig is the destruction of phytate. We need further research to understand how this might benefit the pig.