Carbohydrates of pigeon milk and their changes in the first week of secretion

The carbohydrate content of pigeon crop secretion called pigeon milk (PM) was in the range of 0.9-1.5%. Sugars of trichloroacetic acid soluble (TCA-S) fraction increased by 67% between day-1 and day-5 of secretion while those of TCA- insoluble (TCA-P) fraction remained fairly constant. Sialic acids constituted 5-9% of carbohydrates. The proportion of lipid- and protein-bound sialic acids was 51% and 31% respectively; the former increased from 41% to 68% between day-1 and day-5 whereas the latter decreased from 45% to 21% during the corresponding period. Some of the sugars of PM were fucose (40%), glucosamine (31%), galactose (12%), mannose (9%) and glucose (8%). The free sugars whose content was very low (0.05%) included fucose, mannose, glucose and some unidentified oligosaccharides. The proportion of lipid- and protein-bound sugars was 31% and 63% respectively; the former decreased by 7% from day-1 to day-5 while the latter increased by 11% during the same period. Gel chromatography of PM confirmed the presence of sialic acids and glucosamine; the latter existed both in free and bound form. The nature of changes in the carbohydrate composition of PM in the first week of secretion was more quantitative than qualitative.