362 



THE CaiATES 



The protozoa are an important source 

 of volatile fatty acids. Carroll and Hun- 

 gate (1954) estimated that about 2. 2 kg of 

 volatile fatty acids are produced per 100 

 kg rumen contents in cattle. Gutierrez 

 (1955) calculated that the fermentation 

 acids produced by the rumen holotrichs 

 would constitute a little more than 10% of 

 this amount. If the ophryoscolecids pro- 

 duced an equal amount, then protozoa 

 would provide about 20% of the fermenta- 

 tion products available to their host 

 (Hungate, 1955). As Hungate (1955) re- 

 marked, Gruby and Delafond, who first 

 discovered the rumen protozoa in 1843, 

 guessed that they supplied 1/5 of the food 

 used by their hosts, and the results of 

 investigations during the next 110 years 

 have not significantly modified that esti- 

 mate. 



Another advantage to the host lies in 

 the fact that the holotrichs take up soluble 

 carbohydrates from the medium and con- 

 vert them into stored starch, withholding 

 them for a while and then fermenting them 

 for a long time. This smooths out the 

 fermentation process, which would proceed 

 much more irregularly if it depended upon 

 bacteria alone (Hungate, 1955; Oxford, 

 1955). Entodiniuni and Epidiniuni, too, 

 help smooth out the fermentation process 

 by converting starch into reserve foods. 

 In addition, as Hungate (1959) pointed out, 

 when animals are shifted from hay to 

 grain, there is a period of adaptation dur- 

 ing which lactic acid is produced explo- 

 sively by Streptococcus bovis and may be 

 extremely harmful. The adaptation period 

 may be due to the time needed for Ento- 

 diniuni, Epidiniuni and other bacteria- 

 feeding protozoa to multiply enough to keep 

 the streptococci in check. 



ventral colon) differs from that of the dis- 

 tal 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. Mix- 

 ing occurs at the pelvic flexure of the 

 colon. All horses do not contain all spe- 

 cies. 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 vari- 

 ations. Adam (1953) obtained counts rang- 

 ing 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 rela- 

 tionship of these protozoa to their host, 

 but it is most likely that they are simply 

 commensals. No cysts have been re- 

 ported, and transmission is probably by 

 mouth. Adam (1953) infected a horse with 

 Cycloposthium edentatuni and C. denti- 

 ferum 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. 



FAMILY BUETSCHLIIDAE 



The characters of this holotrichasin 

 gymnostomorid family have been given 

 above (p. 349). 



B. 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 descrip- 

 tions 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 



Genus ALLOIOZONA Hsiung, 1930 



The cilia are present in 3 zones- - 

 anterior, equatorial and posterior. 



Alloiozona trizona Hsiung, 1930 is 

 ovoid, with both ends rounded, and meas- 

 ures 50 to 90 by 30 to 60 /i. The cytostome 

 is at the anterior end and is surrounded by 

 a shallow groove provided with short cilia. 

 The cytopharynx is funnel-shaped. The 



