Last month's newsletter included a research report on research into a novel E. coli phytase expressed in corn, called GraINzyme. Results of that research indicated that adding GraINzyme phytase to diets fed to young growing pigs increased growth performance, digestibility of calcium and phosphorus, and bone mineralization. The comparative effects of GraINzyme and a commercial phytase was not tested in the previous study. Therefore, an experiment was conducted to compare effects of addition of GraINzyme phytase to the commercial phytase AxtraPhy in diets fed to growing pigs.

A total of 48 young growing pigs with an average initial body weight of 11.15 kg were individually housed and used in a 28-day experiment. Pigs were fed one of 6 diets. The positive control was a corn-soybean meal diet in which all nutrients were supplied according to current recommendations. The negative control diet was similar to the positive control except that inclusion of total calcium was reduced by 0.20 percentage units, and inclusion of digestible phosphorus was reduced by 0.18 percentage units. For each of the remaining four diets, a source of phytase was added to the negative control diet: 500 or 1,000 phytase units (FTU) per kg of AxtraPhy (Danisco Animal Nutrition, Marlborough, UK) or 500 or 1,000 FTU/kg of GraINzyme (Agrivida, Inc., Woburn, MA).

At the conclusion of the experiment, pigs were weighed and average daily gain, average daily feed intake, and gain:feed ratio (G:F) were calculated. The right femur was removed from each pig after euthanasia, and bone ash and concentrations of calcium and phosphorus in bone ash were measured.

Average daily feed intake did not differ among treatments (Table 1). However average daily gain, G:F ratio, and final body weight were greater (P < 0.05) in pigs fed the positive control diet than pigs fed the negative control diet. No significant growth performance differences (P > 0.05) were observed if GraINzyme or AxtraPhy where fed at equivalent phytase doses. However, when 500 FTU/kg was fed, AxtraPhy pigs, but not GraINzyme pigs, had average daily gain and final body weight (P > 0.05) that was not different from the positive control pigs.

Bones from pigs fed diets containing either GraINzyme or AxtraPhy had greater (P < 0.05) concentrations (g) of bone ash, bone calcium, and bone phosphorus than pigs fed the negative control diet, but less (P < 0.05) than pigs fed the positive control diet. Bone ash and bone phosphorus weight were greater (P < 0.05) in pigs fed 1000 FTU/kg AxtraPhy than in pigs fed GraINzyme, but not different (P > 0.05) if 500 FTU/kg of either phytase was fed. The percentage of calcium and phosphorus within the bone ash did not differ among dietary treatments.

• Addition of GraINzyme phytase to a P-deficient diet improved growth performance of young growing pigs.
• GraINzyme phytase is effective in releasing phosphorus and calcium bound to phytate, but may require higher inclusion to obtain similar bone mineralization responses as AxtraPhy under conditions tested in this study (calcium and phosphorus reduced by 0.20% and 0.18%, respectively)

Table 1. Growth performance (d 0-28, kg) of pigs fed experimental diets

^a-c Means within a row lacking a common superscript letter are different (P < 0.05).

Table 2. Bone ash, calcium, and phosphorus in pigs fed experimental diets

^a-d Means within a row lacking a common superscript letter are different (P < 0.05).

This report is based on unpublished research by Cristhiam J. Muñoz and Hans H. Stein.