By John Patience, Stacie Gould and Cassie Holloway, Iowa State University; and Dean Boyd, Cate Zier-Rush and Amanda Elsbernd, The Hanor Co.
Last month, we discussed adding phytase at super-dosed levels to nursery diets, and reported substantial benefit from this practice. However, the results of research on super-dosing phytase in growing diets are less definitive.
To try to better answer the question, a study was conducted in a commercial research barn with 2,200 mixed sex pigs fed from 81 pounds to market at about 270 pounds. The test diets contained corn and soybean meal with 15% wheat middlings. The positive control diet was formulated to be balanced for energy and all nutrients, while the negative control diet contained 15 pounds less fat per ton and 0.15% less SID lysine. Both the positive and negative control diets were formulated to contain 225 FTU phytase per pound.
However, our negative control diet was not quite what we had expected; the phytase product contained much higher levels of phytase than indicated on the label, so the negative control diet contained about 500 FTU phytase per pound rather than the formulated 225 FTU per pound. Thus, the negative control diet already contained phytase approaching the lower end of what would be considered super-dosed levels. The super-dosed diets, of which there were three, contained 680, 1,034 and 1,134 FTU per pound.
Even so, the higher levels of phytase increased feed efficiency by 1% on both a live (P = 0.028) and carcass weight basis (P = 0.040). The higher levels of phytase also tended to improve growth rate on a live weight basis (P = 0.076) and on a carcass weight basis (P = 0.067). The elevation in gain resulted in an additional 2 pounds of carcass weight sold at closeout (P = 0.043).
This study did not really evaluate the impact of super-dosing, because of the higher-than-expected level of phytase in the control diet. However, it did demonstrate that exceeding 500 FTU of phytase per pound can be beneficial, and the magnitude of the improvement can be financially advantageous to the producer.
It is important to differentiate between the use of phytase to meet the pig’s basic requirement for phosphorus, and to use it at super-dosed levels to advance pig performance for reasons not explained by improved phosphorus availability. Phytase is routinely added to pig diets when supplemental phosphorus is needed to meet the pig’s requirement for phosphorus and thus avoid deficiency symptoms. Whenever the basal ingredients in a diet — such as corn and soybean meal — do not supply enough phosphorus, nutritionists previously would add monocalcium or dicalcium phosphate. Now, nutritionists will select phytase ahead of these mineral supplements because it is much less expensive, and better for the environment.
Typically, 250 to 500 FTU phytase per pound of diet are used for this purpose. Now, monocalcium or dicalcium phosphate are only added to the diet when phytase cannot fully meet the pig’s requirement for phosphorus.
There is one note of caution when using phytase. Excess calcium has been shown to diminish the ability of phytase to release phosphorus. Indeed, if calcium becomes too high in the diet, phytase can become completely ineffective. There is a growing body of information on the correct ratio of calcium to phosphorus, but for example, a 1.5:1 ratio of calcium to total phosphorus has been shown to reduce phytase effectiveness by about 50% and a ratio of 2.3:1 totally negated the value of phytase in the diet (Beaulieu et al., 2007).
Beaulieu, A.D., M.R. Bedford and J.F. Patience. 2007. Supplementing corn or corn-barley diets with an E. coli derived phytase decreases total and soluble P output by weanling and growing pigs. Can. J. Anim. Sci. 87:353-364.