Ciliates of Equids
Just as great a variety and number of ciliates swarm in the cecum and colon of equids as in the rumen and reticulum of ruminants. Hsiung (1930) gave descriptions of 51 species of 25 genera in his monograph, while Strelkov (1939) listed 87 species and forms. The fauna of the proximal large intestine (the cecum and ventral colon) differs from that of the distal large intestine (the dorsal and small colons). Strelkov (1939) listed 25 species and forms in the proximal fauna, 43 in the distal fauna, and 7 common to both. Mixing occurs at the pelvic flexure of the colon. All horses do not contain all species. Strelkov (1939) found an average of 7.7 species per horse in the proximal fauna and 16.6 species per horse in the distal fauna.
The highest populations of ciliates occur in the left dorsal colon and the lowest in the cecum (Adam, 1951). The ciliate population shows large daily variations. Adam (1953) obtained counts ranging from 1000 to 47,000 per ml in the cecum and from 14,000 to 3,072,000 per ml in the ventral colon of a single horse at different times and on different rations.
Almost nothing is known of the relationship of these protozoa to their host, but it is most likely that they are simply commensals. No cysts have been reported, and transmission is probably by mouth. Adam (1953) infected a horse with Cycloposthium edentatum and C. dentiferum by feeding fresh colon contents by stomach tube. Forsyth, Hirst and Oxford (1953) found that Cycloposthium stores a polysaccharide with a highly branched molecular structure closely similar to that of amylopectin.