Phytase added to swine diets reduces the phosphorus in manure, but does not impact pig performance or the cost of feed rations, according to researchers at Iowa State University and Kirkwood Community College, Cedar Rapids, IA. The project was funded by the Iowa Pork Industry Center.

Four replications of 100 crossbred pigs were tested in Kirkwood's 600-head, double-curtain sided, totally slotted facility. Fifty pigs, averaging 90 lb., were assigned by sex to the control and phytase diets. Barrows and gilts alternated between test and control diets.

Phytase activity is expressed as phytase units (FTU)/unit of feed. Typical inclusion rate for corn/soy diets is 115 to 150 FTU/lb. For example, BASF's Natuphos 5000 contains a guaranteed minimum of 5,000 FTU/g. or 2,268,000 FTU/lb. For the project, split sex diets were formulated to be nutritionally comparable in four phases with high oil corn, soybean meal and from 125 to 150 FTU/lb. of phytase.

Liquid and solid manure samples were taken every two weeks and tested for nitrogen, phosphorus and potassium. Initial water dilution levels in the shallow manure pits under the test and control pens were standardized to 30 gal. of water per pig. The pigs came off test at approximately 240 lb.


Feeding phytase reduced the phosphorus (P2O5) in the solid manure by 17% and lessened the liquid manure P2O5 by 22%. The average daily gain was 2.03 lb. for the control pigs and 1.97 lb. for the phytase-fed pigs. Feed efficiency was 2.91 for the control group, 2.75 for the phytase group. The cost of the phytase diets ranged from $0.59 to $1.20/ton less than the control diets.

Researchers: Larry McMullen, Iowa State University Extension Service; Arlin Karsten, DVM, Kirkwood Community College. Contact McMullen at (319) 462-2791 or email