Estimation of ileal output of gastro-intestinal glycoprotein in weaned piglets using three different methods

Mucin is the main constituent of gastrointestinal mucus and is responsible for its physicochemical and physiological properties. Previous studies have suggested that this glycoprotein represents a major component of undigested endogenous protein at the ileum. The aim of the study was to estimate the ileal output of this glycoprotein using three methods: direct ELISA, hexosamine-based method and ethanol precipitation. For setting up the ELISA assay, the glycoprotein was isolated from intestinal mucus scraping by cesium chloride density gradient ultracentrifugation and a rabbit hyperimmune plasma was raised against the purified glycoprotein. Ileal outputs of hexosamine and glycoprotein were measured in weaned piglets fed a control diet (C) based on casein or diets which contained 50% crude protein supplied by white (WCP) or black (BCP) chickpea. The hexosamine output was higher (P < 0.05) with the WCP diet (2.3 and 1.5 g x kg(-1) of dry matter intake for glucosamine and galactosamine, respectively) than with diet C (1.1 and 0.7 g x kg(-1) of DMI). The hexosamine-based and ethanol precipitation methods, but not the ELISA, showed significant differences between the diet treatments (P < 0.05). Although hexosamine-based and ethanol precipitation methods for the estimation of ileal glycoprotein appeared to be more satisfactory than the developed ELISA to display diet effects in this study, it remains to be determined whether the higher glycoprotein data variability observed with ELISA reflects the actual biological variability of the phenomenon or not.