Digestion of soybean globulins, glycinin, α-conglycinin and β-conglycinin in the preruminant and the ruminant calf

Two experiments involving either preruminant (exp. 1) or ruminant (exp. 2) fistulated calves were conducted to study the in vivo digestion of glycinin, α-conglycinin and β-conglycinin from soybean. It was incorporated as a flour (product A, antigenic in vitro) or a protein concentrate (product B, non antigenic in vitro) in milk replacers (exp. 1), or as a meal (product C, antigenic in vitro) in a weaning starter (exp. 2). ELISA detection of residual globulin immunoreactivity was determined on ileal digesta in exp. 1, and on duodenal, ileal and faecal digesta in exp. 2. Ileal flow of glycinin, α-conglycinin and β-conglycinin represented 10.3, 1.2 and 0.9% of corresponding globulin amounts ingested, in the case of product A (exp. 1). Immunoreactive α-conglycinin could only be detected in ileal digesta (1.3% of intake) of calves fed the diet containing product B. In exp. 2, immunoreactive globulins entered the duodenum in low amounts (below 1% of respective intake), especially after weaning. Accordingly, their flow at the ileum and in feces, although measurable, had no meaning from the nutritional point of view. Fermentation in the rumen of weaned calves appeared to be efficient in inactivating most of the potentially harmful dietary constituents. Key words: Soybean, protein, digestion, calf, weaning, glycinin