Evaluation of the Neonatal Pig As a Model for Infant Nutrition: Effects of Different Proportions of Casein and Whey Protein in Milk on Nitrogen Metabolism and Composition of Digesta in the Stomach

Abstract

Summarygiven formulas containing predominantly whey proteins did Abbreviation DM, dry matterSimilarities in the digestive system of man and the pig suggest that results of studies on digestion and nutrition in the pig may be applicable to man (9). Some similarities in neonatal glucose metabolism have also been demonstrated (1 3). Other studies in neonatal pigs have assumed that results may be relevant, for example, in studies on protein nutrition (28, 23). However, no systematic comparisons of protein utilization have been made between the two species during the neonatal period. Such comparisons must inherently be rather superficial since ethical considerations limit the data on protein nutrition and digestion from infants to parameters of growth, nutrient retention, and analyses of blood.Between species, there is considerable variation in the proportions of casein and whey proteins in the protein of the milk. Whey proteins account for about 20, 50, and 80% of the total protein in bovine (26), porcine (27), and human milks (16), respectively. The desire to "humanize" dried milk formulas for infants which were previously based on unmodified bovine milk gave rise to studies in which formulas containing predominantly casein or whey protein were compared in infants. At the time of these studies, it was believed that whey proteins contributed only 60% of the total protein in human milk (16). Although not all differences were statistically significant, low birth weight infants show improved N retention (2) and reduced concentrations of urea in plasma (24), suggesting a better utilization of the protein.Increasing the protein concentrations in the milk also reduced the efficiency of protein utilization (24). In term infants, plasma urea concentration was also reduced by a formula containing predominantly whey proteins (19), but a recent study detected no differences in the utilization of casein and whey proteins (17). As it was desired to test the validity of the neonatal pig as a model for infant nutrition, milks containing either casein or whey as the predominant protein have been compared at two levels of protein intake in neonatal pigs. In view ofthe substantial proportion of whey proteins in sow's milk, enriching a milk substitute with whey proteins could also have important implications in the rearing of early weaned pigs.These studies have also been extended to compare gastric digestion and emptying following slaughter under standardized conditions. I n vifro studies in our laboratory (unpublished) showed that the coagulation time following the addition of bovine chymosin was inversely related to the casein content of the milks. Therefore, an increase in the proportion of whey protein might increase the rate of gastric emptying. Previous work has shown that whole cow's milk quickly coagulated in the stomach of the 4-week-old pig, followed by rapid draining of the whey (6). Also, the amount of dry matter in the stomach was usually decreased when milk was replaced by noncoagulating proteins derived from soybea...

Nutritional Regulation of Gastric Secretion, Digestion and Emptying

“…Casein and a-protein were more completely hydrolysed and the digesta left the stomach faster than raw or heated soya bean. A series of studies with 28-d-old piglets killed 1 h after feeding showed that the appearance of trichloroacetic acid (TCA)-soluble N in gastric contents was slower for bovine milk proteins than for fish proteins (Newport, 1979), isolated soya-bean protein (Newport, 1980) or a whey-supplemented milk (Newport & Henschel, 1984); heat-damaged milk proteins were less rapidly digested than undamaged proteins (Braude et al 1971).…”

“…Further evidence of the complexity of emptying of milk or casein-based diets is shown by the more rapid emptying of human milk than of infant formulas in infants (Cavell, 1981); this may be related in part to the amounts of whey protein as a percentage of total protein in bovine (20), porcine (50) and human (80) milks. Thus, Newport & Henschel (1984) found that the gastric emptying rate of protein was highest for diets with a high whey:casein ratio. The nature of the curd formed in the stomach after consumption of bovine milk is also related to the rates of gastric emptying; soft curds from UHT-treated or cultured milk emptied faster than the hard curds formed from raw or pasteurized milk in the studies by Meisel & Hagemeister (1984).…”

Enteral administration of bacteria fermented formula in newborn piglets: A high fidelity model for necrotizing enterocolitis (NEC)

“…The hypomotility of the premature infant allows for stasis resulting in prolonged interaction of gastrointestinal flora with enteral feeds as well as prolonged contact of the mucosa with potentially injurious byproducts of this interaction. Brush border enzymes beta-galactosidase (lactase) and alpha-glucosidases (sucrase, isomaltase, maltase, and glucoamylase) reach functional maturity at different gestational stages with lactase maturing the last between 30–34 weeks [ 43 , 44 ]. As the premature infant bowel is exposed to lactose-containing cow’s milk-based formula, the limited ability of the neonate’s small bowel to digest lactose provides the proximal colonic flora extra substrate to ferment.…”

Growth Responses of Preterm Pigs Fed Formulas with Different Protein Levels and Supplemented with Leucine or β-Hydroxyl β-Methylbutyrate

“…The BUN values measured during PN are comparable to preterm infants receiving primarily parenteral nutrition during the first week after delivery [ 48 ]. The low and sometimes undetectable BUN levels for preterm pigs fed the low protein formulas are comparable to those of term pigs fed low protein formulas [ 49 ] and preterm infants fed a low protein formula that still promotes growth [ 50 ]. The low BUN values suggest that the majority of the protein was partitioned into accretion of lean body mass, with little catabolism of dietary or tissue protein along with lower energetic costs for nitrogen disposal.…”