Recovery of N-15-lactoferrin is higher than that of N-15-casein in the small intestine of suckling, but not adult miniature pigs

Performance of biological functions of lactoferrin in the small intestine r equires at least some resistance to degradation. Therefore, we studied prec ecal digestibility of lactoferrin in comparison to casein both in suckling and adult miniature pigs, applying N-15-labeled proteins. In study 1, 43 pi glets (10-d-old), deprived of food for 12 h received 10 mt of sow's milk su pplemented with 120 mg of N-15-labeled protein (porcine or bovine lactoferr in or bovine casein). Piglets were anesthetized 150 min later, after which the small intestine was excised, cut into three sections, and chyme was col lected. In study 2, nine food-deprived boars fitted with T-canulae at the t erminal ileum were given two semisynthetic experimental meals (204 g) in a cross-over design, 2 wk apart. One contained 7.5% (g/100 g) N-15-labeled bo vine casein, the other 1.25% N-15-labeled bovine lactoferrin. Both were adj usted to 15% total protein with nonlabeled casein. Ileal chyme was collecte d from the canula over 33 h postprandialy. All diets contained the indigest ible marker chromic oxide. N-15-digestibility of lactoferrin, both porcine (84.4 +/- 3.2%) and bovine (82.3 +/- 4.8%), was significantly lower than ca sein digestibility (97.6 +/- 0.5%) in the distal small intestine of sucklin g piglets (P < 0.05). Based on immunoblotting after acrylamide electrophore sis, 4.5% of non- and partially digested lactoferrin was found in the last third of the small intestine of piglets. In adult miniature pigs there was no difference in N-15-digestibility of bovine lactoferrin compared to bovin e casein (90.7 +/- 1.9% vs. 93.9 +/- 1.0%, P > 0.05). In suckling miniature pigs, the reduced digestibility of lactoferrin may provide the prerequisit e for biological actions along the whole intestinal tract. The source of la ctoferrin, porcine or bovine, made no difference in this respect.