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Summary. Six rumen-fistulated and defaunated wethers were fed twice daily a pelleted diet of barley and dehydrated lucern at a rate of 50 g dry matter/kg body weight °-!5. Two months later, the sheep were divided into three equal groups. Each group was then inoculated in the rumen with one of the following three genera of protozoa : Polyplastron multivesiculatum (P), Entodinium sp. (E), or lsotricha prostoma (I). After two months, each group was subdivided and inoculated with an additional genus to obtain two sheep for each P + E, P + I and E + I combination. After an additional two months, two sheep were inoculated with a mixture of several genera to restore them to a conventional state. At the end of each of the four two-month periods, the total digestibility of organic matter (OM), acid detergent fiber (ADF), nitrogen (N) and fermentation in the rumen were measured.The P + E genera combination could not be obtained because E disappeared when the sheep were inoculated with the P species. However, these two genera can coexist in a rumen containing at least four different genera of protozoa.OM and ADF digestibilities were improved mainly by inoculating the P genus and, to a lesser extent, the E genus, but the effect of I was negative. N digestibility tended to be higher after ciliate inoculation, compared to the defaunated state. Furthermore, the pH in inoculated sheep was generally lower, and volatile fatty acid (VFA) and ammonia levels were higher.The composition of the VFA mixture was strongly influenced by inoculation with the E genus : the propionic acid proportion increased at the expense of the acetic and butyric acid proportions. This result was confirmed by the lower CH 4/ C0 2 ratio observed in the rumen gas composition in sheep inoculated with the E genus. With P alone or with other ciliates, the butyric acid proportion increased. The rumen lactic acid concentration increased after inoculation with the I genus. In the conventional animals, fermentation patterns were similar to those observed in the P-inoculated animals but the differences increased and became significant.Of the three ciliates studied, the P genus had the greatest effect on the digestive parameters which were similar to those found in conventional sheep. This effect could be explained by the ability of the P genus to hydrolyse and ferment most carbohydrates and by its predatory action on bacteria and protozoa.Introduction.

1. The effect of protozoa on digestion in the rumen was studied using either defaunated or faunated sheep. 2. Six wethers, each fitted with rumen and simple duodenal cannulas, were given two isonitrogenous diets containing either lucerne (Medicago sativa) hay (diet L) or sodium hydroxide-treated wheat straw (diet S). The diets were given in eight equal portions per day at 3-h intervals. The mean intake of dry matter, 53 g/kg body-weight0 75 per d, was similar for the two diets and each diet had a similar digestible organic matter content. Diet L promoted a large protozoal population and was rich in nitrogen sources of low rumen-degradability, while diet S supported a smaller protozoal population and was rich in rumen-degradable N.3. Digesta flow at the duodenum was estimated by means of a dual-marker technique usingchromium-mordanted lucerne hay and polyethylene glycol as markers. The microbial flow at the duodenum was estimated using diaminopimelic acid (DAPA), nucleic-acid purine bases (PB) and 35S incorporation simultaneously. The different microbial markers were compared in the defaunated sheep. Protozoal N contribution was estimated in faunated sheep.4. Defaunated sheep had lower rumen ammonia concentrations and molar proportions of butyric acid than faunated sheep, but they had higher molar proportions of propionic acid.5. Rumen organic matter digestion was reduced by defaunation, but this decrease was compensated for by increased intestinal digestion.6. There was a net increase of N flow (approximately 10 g/d) between mouth and duodenum in defaunated sheep. This was explained by increases in both microbial and dietary N flows from the rumen compared with faunated sheep.7. The influence of protozoa on solid-and liquid-phase retention times in the rumen is discussed, as well as the protozoal contribution to microbial N flow in the duodenum of faunated sheep.Although some work has demonstrated the proteolytic activity of protozoa (Warner, 1956;Williams et al. 1961 ; Abou Akkada & Howard, 1962), the quantitative contribution of these micro-organisms to the degradation of feed protein in the rumen is still unclear. Moreover, few in vivo experiments have examined the effect of protozoa on rumen bacterial protein synthesis (Lindsay & Hogan, 1972;Ushida et al. 1984). Recently, Australian workers (Bird & Leng, 1978; Bird et al. 1979) demonstrated the positive effect of defaunation on animal growth when given a high-energy diet with low content of rumen-undegradable protein.These results suggest that defaunation increases protein flow to the small intestine as suggested by Veira et al. (1984), and this increase in the protein available to the animal has a marked effect on animal performance under circumstances in which the intestinal protein supply is limiting.The objective of the present study was, therefore, to investigate quantitatively the contribution of protozoa to nitrogen digestion in sheep, and particularly the effect of defaunation on the passage of dietary and microbial N to the duodenum. The protozoal ...

Les méthodes de dosage de l'amidon sont nombreuses, mais aucune n'est à la fois spécifique et rapide. La