Interspecific variation in sugar and amino acid transport by the avian cecum.

Previous studies of cecal sugar and amino acid transport in the domestic chicken led to a widely held generalization that the avian cecum is unimportant as a site of nutrient transport. In fact, we found that the uptake capacity of the cecum for hexose sugars and amino acids is substantial in some species of birds. Cecal transport of glucose was measurable in all five study species (Canada goose, sage grouse, domestic chicken, red-necked phalarope, and rock dove), approached or exceeded intestinal levels in the grouse and phalarope, and accounted for between 0.1% (rock dove) and 49% (sage grouse) of the whole gut's integrated uptake capacity. Proline uptake averaged higher in the proximal portion of the cecum than in any region of the small intestine for all species but the goose. The ceca contributed between 2% (rock dove) and 25% (sage grouse) of the gut's integrated uptake capacity for proline. Similar ranges were found for fructose, lysine, leucine, and aspartate. Future studies should be undertaken to search for phylogenetic and ecological correlates of the interspecific variation in cecal transport and to determine how nutrient transport integrates with other functions of the avian cecum.