faunation decreased acetate and butyrate production, while it increased propionate production.Defaunation decreased also total VFA production. These effects were observed with both diets, but were clearer under the presence of a larger protozoal population promoted by FC diet.Defaunation decreased methane and carbon dioxide production with FC diet, while it had no clear effect on these gas production with AF diet. Consequently protozoa enhance acetate, butyrate, methane and carbon dioxide production and depress propionate production.Defaunation, therefore, may improve energy efficiency of diets, if total VFA production is not greatly depressed.However their quantitative contribution to these end products may depend on their population size. Jpn. J. Zootech. Sci., 57 (1): 71-77, 1986 Key words: defaunation, methanogenesis, VFA, sheep rumen Role of protozoa on the rumen fermentation has been widely studied in last 20 years1-10) and the important contribution of protozoa in butyrate and ammonia production is demonstrated. As to protozoal contribution to other volatile fatty acids, such as acetate and propionate production, there have been some disagreements between results published so far (JOUANY et al.)8). Magnitude of effects of defaunation may depend on characteristics of diet given to the experimental animals, since the diet influences not only the size of protozoal population but also the type of bacterial population.Protozoa produce hydrogen11) which will be further utilized in methane formation. It is, therefore, probable that defaunation promotes a decline of methane production. However the effect of defaunation on the methanogenesis may be detectable under some particular dietary conditions in which effect of defaunation on acetate and propionate is clear, because methane formation is linked with acetate production12) and decrease in methane formation coincides with increase in propionate production13). It is likely that protozoal population size is one of the major factors which decide their quantitative contribution to the methane production.In the present work, the effect of defaunation on rumen VFA and gas production was studied using sheep fed two types of diets which promote two different size Jpn. J. Zootech. Sci., 57 (1): 71-77 71 1986

It has long been known in the field of plant physiology that nitrate taken up by a cell as the anion NO3-is partly reduced and assimilated to amino acids and protein.However, when the intake of nitrate by the plants exceeds the consumption, nitrate is accumulated in large amounts in the plants.When cattle or sheep are fed with the forage containing much nitrate, there is a danger of nitrate poisoning2). Even if the concentrations of nitrate were not so large as to be lethal to the animals, the economic performance of the ruminants would be reduced. That is, the high concentrations of nitrate in the feed seem to cause an abortion8), loss in body weight gains29) and decrease in milk production7) of the ruminants. Therefore, it is important for a stockman to have an accurate knowledge on the concentrations of nitrate in forage crops in his field.

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