Sites of phytase activity in the gastrointestinal tract of young pigs

Abstract

The sites of supplemental phytase activity in the gastrointestinal tracts (GIT) of young pigs fed added microbial phytase were determined in two tests. In Test 1, samples of diets and GIT (stomach, upper and lower small intestine) contents were taken from pigs (BW = 20.3 kg) that had been fed a soybean meal-based semi-purified diet containing two levels of available P (0.5 and 1.6 g kg −1 aP), without or with added microbial phytase (1050 U kg −1 diet) for 5 weeks. There was no detectable phytase activity in the diets and GIT contents of pigs fed the basal diets without added phytase, and phytase activity did not differ for diets or GIT contents between the two dietary P levels. For pigs fed diets with added phytase, phytase activity in the digesta from stomach was higher ( P < 0.001) than that from upper small intestine (51 or 31% of diet activity). No phytase activity was detectable in the digesta of the lower small intestine. In Test 2, samples of diets and GIT contents were taken from young pigs (BW = 16.7 kg) that had been fed a corn and soybean meal diet with added microbial phytase (750 U kg −1 of diet) containing one of three levels of citric acid (0, 15, and 30 g kg −1) for 4 weeks. Adding 30 g kg −1 citric acid decreased ( P < 0.06) phytase activity in the stomach digesta; but there was no difference between the 15 and 30 g kg −1 added citric acid. About 40% of the added phytase activity remained in the digesta of the stomach from pigs fed the diet without added citric acid; whereas, only 27% of the phytase activity remained in the stomach digesta from pigs fed the diet with added citric acid. Again, phytase activity in the digesta from stomach was higher ( P < 0.05) than that in digesta from upper small intestine (16 and 10% of added activity, respectively for diets without and with citric acid). As in Test 1, no phytase activity was detectable in lower small intestine digesta. In summary, the stomach is the site of highest added microbial phytase activity most likely because of a more favorable pH and lower protease activity.