Growth, digestion, and protein metabolism in neonatal pigs given diets containing whey as the predominant or only source of milk protein.

Milk substitutes containing ratios of casein/whey protein ranging from 80:20 to 0:100 were given to neonatal pigs. A ratio of 60:40 gave maximum growth rate, efficiency of feed utilization and nitrogen retention, and the lowest concentration of urea in blood plasma. This ratio is close to that in sow's milk, suggesting the hypothesis that in each species the milk may be adapted to the protein requirements of their young; by analogy, a casein/whey protein ratio of 20:80 in humanized milk formula might lead to more efficient protein utilization by the infant. In general, changes in the proportion of casein and whey proteins in the diet produced similar effects on the free amino acids in blood plasma as were found in clinical studies reported in the literature, providing further evidence of similarities in the protein metabolism of infants and neonatal pigs. The amount of nitrogen in the digesta remaining in the stomach at 1 h after a meal indicated that whey proteins empty from the stomach more rapidly than casein.