The effect of microbial phytase on true and apparent ileal amino acid digestibilities in growing-finishing pigs

¹ Agriculture and Agri-Food Canada, Sherbrooke, Québec, Canada, J1M 1Z3
² INRA, USC340 Animal et Fonctionnalités des Produits Animaux, INPL-ENSAIA, BP 172, F-54505 Vandoeuvre-les-Nancy, France

^* To whom correspondence should be addressed. E-mail: pomarc{at}agr.gc.ca.

	Abstract

Ten 56-d old 15-kg barrows were surgically fitted with a post-valvular T-cecum cannula at the ileo-cecal junction to evaluate the effect of microbial phytase on apparent and true ileal AA digestibility and N utilization. A semi-purified corn starch and soybean meal-basal diet was formulated to contain 3.4 Mcal DE/kg, 17.0% CP, 0.8% Ca, and 0.6% P but had a low phytate-P concentration (0.13%). Chromic oxide and dysprosium chloride were used as indigestible markers. The basal diet was supplemented with 0 or 1,000 phytase units/kg microbial phytase. Postprandial plasma urea-N and -amino N, excretion of Ca, P, and N in feces and urine and ileal AA digestibilities were determined 3 times at 4-wk intervals starting at 70 d of age. The homoarginine (HA) method was used to determine endogenous AA flow by replacing 50% of the basal protein by guanidinated protein. Microbial phytase had no effect on apparent ileal digestibility (AID) or on true ileal digestibilities of N and most AA but did increase AID for arginine (P = 0.006) and methionine (P = 0.037). However, in HA diets, phytase increased the AID of CP (P = 0.01) and several AA. Addition of microbial phytase had no effect on the postprandial -amino N concentrations in plasma but increased the overall plasma urea-N concentrations (P = 0.035). Pigs fed phytase-supplemented diets had decreased P in feces (P = 0.003) and greater P in urine (P = 0.001) but comparable total P excretion than pigs fed no phytase-supplemented diets. In conclusion, the addition of phytase to semi-purified soybean meal basal diet did not affect the AID of several AA. Also, differences between basal and HA diets on N digestibilities indicated that that guanidination may limit the utilization of the homoarginine method in the determination of endogenous protein losses.

Key Words: amino acids, apparent ileal digestibility, homoarginine, phytase, pigs, true ileal digestibility