Digestion of colostrum by the preruminant calf: Digestibility and origin of undigested protein fractions in ileal digesta

Abstract

Four diets (SMP, ML, DC and DCLC) containing 24, 18, 53 and 19% crude protein on a dry matter basis, respectively, were given to ileo-cæcal cannulated preruminant calves. In the SMP diet, protein was provided by skim milk powder. The ML diet was a mixture of raw whole milk and lactose. The DC and DCLC diets were first milking colostra diluted with water (DC) or water, lactose and UHT cream (DCLC). The apparent ileal digestibility of N was low with the DC and DCLC diets (0.71 and 0.70 vs. 0.92 with the SMP and ML). Comparisons of AA profiles suggested that could be due to: (1) an increased loss of endogenous protein (+ 480 and + 200% for DC and DCLC, respectively), (2) an incomplete digestion of immunoglobulins G (IgG) which constituted 49 and 42% of digesta protein for DC and DCLC. The proportion of immunoreactive IgG found by radial immunodiffusion was similar for DC digesta (47%) but lower for DCLC (6%). Indeed, immunoblotting of non-reduced protein showed intact and/or almost intact IgG were more abundant for DC than DCLC. However, in reduced samples, intact and/or slightly degraded γ heavy chains were abundant for both. In contrast, only traces of IgG were detected in SMP and ML digesta.