Milk Protein - More Than Just Amino Acids? A Study On Growth And Growth Biomarkers In Piglets

Some studies indicate that milk protein may stimulate growth and growth factors beyond what can be expected from supplying the dietary amino acids, i.e. milk proteins may have bioactive functions. The aim of this study was to test this by using blends of plant and milk proteins in diets formulated to contain digestible amino acids according to requirements. Ninety-six piglets were divided into 48 pens and fed 4 different diets for 3 weeks for measurement of performance. Protein in the diets came from either 100% milk, 50% milk + 50% rice protein, 50% milk + 50% rape seed protein, or 50% rice + 50% rape seed protein and supplemented with crystalline amino acids to meet the requirements of piglets. At the end of the study, a 1-h postprandial blood sample was taken and a liver sample for gene expression analysis. All pigs had a high gain and a low FCR, but feed intake and daily gain was lowest and FCR poorest in the diet containing only plant protein. The differences were not associated with differences in growth insulin, IGF-1, or hepatic gene expression of genes related to growth and protein metabolism. Plasma levels of all essential amino acids except cysteine and lysine decreased markedly when fed a diet containing only plant protein. However, there were no indications that milk protein, beyond a favorable amino acid composition and high digestibility, specifically stimulated growth factors and other biomarkers of growth.