In an effort to find alternative sources of phytase for swine diets, University of Wisconsin researchers have genetically engineered a strain of alfalfa that expresses high levels of the enzyme. If the alfalfa source could be used in swine diets, the product may have an improved shelf life and serve as a more cost-effective phytase source.

Supplementing a corn-soybean meal diet with transgenic alfalfa leaf meal phytase was evaluated by measuring pig growth, apparent calcium and phosphorus digestibility and gain in bone mineral content.

Twenty 22-lb. barrows were fed corn-soybean meal basal diets with 0.45, 0.50, or 0.55% total phosphorus without phytase, plus 0.45% total phosphorus diets with either 200 or 400 FTU/kg. of diet. Only 2.66 lb. or 5.33 lb. of alfalfa leaf meal per ton of complete diet was required to obtain the desired levels of phytase activity. Diets were formulated to contain 1.15% lysine, and a calcium-to-total-phosphorus ratio of 1.1:1.

Two replicates of 10 barrows were individually penned and fed their respective diets for 16 days in Trial 1, 13 days in Trial 2. Pigs spent four days in metabolism crates for total fecal and urine collection to analyze phosphorus and calcium content. Dual-energy x-ray absorptiometry scans initially determined bone mineral content. Pigs were re-scanned on days 1 and 4 of the collection period.

Pigs fed 0.45% phosphorus diets supplemented with 200 or 400 FTU/ kg. showed an 18-28% increase in ADG and an 18-24% increase in ADFI compared to pigs fed diets supplemented with only 0.45% total phosphorus.

In pigs fed 200 FTU/kg., phosphorus retention improved by 32%; and calcium retention improved by 35%. No differences were detected in phosphorus or calcium digestibility or fecal phosphorus excretion.

Phytase supplementation of 200 or 400 FTU/kg. improved bone mineral content gain over the trial by 72% and 76%, respectively.

The addition of 200 or 400 FTU/kg. to the 0.40% phosphorus diet was equal to adding 0.48% or 0.50% phosphorus to the diet. Thus, 200 FTU/kg. from transgenic alfalfa leaf meal was equal to 0.08% added phosphorus.

Researchers: Kari L. Saddoris and Tom D. Crenshaw, University of Wisconsin, Madison. Contact Crenshaw at (608) 263-4423, or e-mail crenshaw@calshp.cals.wisc.edu.