nutrient Metabolism Gastric Emptying Regulates the Kinetics of Nitrogen Absorption from 15N-Labeled Milk and 15N-Labeled Yogurt in Miniature Pigs1'2

Thirty-six miniature pigs divided into two groups of 18 animals were fed '^rH-labeled milk or yogurt. Polyethylene glycol 4000 was added to the diets as a non-absorbable marker of the liquid phase. Animals were slaughtered 1, 2, 4, 8 and 12 h after meal in gestion, and the gastrointestinal tract was removed and divided into 10 parts. Polyethylene glycol, total nitrogen and '^N enrichment were measured in the digesta. Both the intestinal delivery of the liquid phase and the nitrog enous fraction of the chyme were delayed more in pigs fed yogurt than in pigs fed milk. No stimulatory effect of diet ingestion on endogenous nitrogen secretion was found. Both milk proteins and yogurt proteins were highly digestible: 93% of the exogenous nitrogen disap peared 12 h after feeding. The kinetics of exogenous nitrogen delivery into the intestine was correlated (r = 0.999 for milk and / = 0.974 for yogurt) with that of exogenous nitrogen absorption. These results suggest that milk proteins are rapidly absorbed after they reach the intestine. Gastric emptying is a major factor con trolling the kinetics of milk nitrogen absorption. J. Nutr. 124: 1970-1977, 1994.