The intestinal protozoan parasite Spironucleus spp. is associated with disease in pheasants (Phasianus colchicus) and other game birds. Affected flocks suffer considerable morbidity and mortality. Intestinal histopathology is minimal, but affected birds present with diarrhoea and loss of weight, consistent with malabsorption/secretory abnormalities. To examine the mechanism by which Spironucleus spp. causes disease, we studied fluid transport in the small intestine of normal and diseased pheasants.

Absorption was investigated using everted sacs of small intestine (adapted from Wilson & Wiseman (1954), taken from birds killed humanely for diagnostic purposes). Saline, designed to approximate the constituents of pheasant plasma, comprised (mM): NaCl 132, KCl 4, Na₂HPO₄ 4, NaHCO₃ 25, MgCl₂ 1, CaCl₂ 1, glucose 20, glycine 1, pH 7.4 when bubbled with 5 % CO₂ and 95 % O₂ at 37 °C, and osmolality 337 ± 5 mosmol kg^-1. Intestinal cylinders were everted using Hartmann’s aural forceps, sealed at their distal end with ligatures (Ethicon Mersilk, 3.5 metric) and tied to 1 ml syringes. The serosal side of the sac was filled with saline and the mucosal side was open to the bath. Absorption was followed by measuring the change in weight of the preparation and is given in µl (g dry tissue min)^-1. The effects of ion substitutions (Na⁺ replaced with choline; Cl^– replaced with NO₃^–; glucose with mannitol) and various inhibitors (amiloride 1 mM; furosemide, ouabain and phloretin, all 100 µM) were examined.

Mean absorption rate in healthy birds was 56 ± 6 µl (g min)^-1 (means ± S.E.M., n = 32). This was inhibited by 84 ± 3, 64 ± 13 and 57 ± 9 % by ouabain, Na⁺ and Cl^– substitution, respectively (n = 4; P < 0.05; Student’s paired t test). Removal of mucosal glucose inhibited absorption by 50 ± 4 %, whilst exclusion of glycine was without effect. Mucosal application of amiloride, furosemide and phloretin all inhibited absorption by > 30 %. In birds infected with Spironucleus spp., absorption fell to 24 ± 4 µl (g min)^-1 (n = 18; P < 0.0001; Student’s unpaired t test).

These findings show that absorption in pheasant intestine is driven by serosal Na⁺/K⁺ pumps, coupled to mucosal Na⁺ entry via amiloride-sensitive and Cl^–-dependent mechanisms, together with mucosal entry pathways for glucose. Thus pheasant intestine shares many of the features described for chicken small intestine (Barfull et al. 2002). Infection with Spironucleus spp. was associated with reduced absorption rates, which may be important in its pathology.

This work was supported by the Game Conservancy Trust. We thank Dr A.E. Hill and Dr B. Shachar-Hill for advice with methodology.