The Role of Protozoa in Feed Digestion - Review -

  • Jouany, J.P. (INRA, SRNH, Centre de Clermont-Theix) ;
  • Ushida, K. (INRA, SRNH, Centre de Clermont-Theix)
  • Published : 1999.01.01


Protozoa can represent as half of the total rumen microbial biomass. Around 10 genera are generally present on the same time in the rumen. Based on nutritional aspects they can be divided in large entodiniomorphs, small entodiniomorphs and isotrichs. Their feeding behaviour and their enzymatic activities differ considerably. Many comparisons between defaunated and refaunated animals were carried out during the last two decades to explain the global role of protozoa at the ruminal or animal levels. It is now generally considered that a presence of an abundant protozoal population in the rumen has a negative effect on the amino acid (AA) supply to ruminants and contribute to generate more methane but, nevertheless, protozoa must not be considered as parasites. They are useful for numerous reasons. They stabilise rumen pH when animal are fed diets rich in available starch and decrease the redox potential of rumen digesta. Because cellulolytic bacteria are very sensitive to these two parameters, protozoa indirectly stimulate the bacterial cellulolytic activity and supply their own activity to the rumen microbial ecosystem. They could also supply some peptides in the rumen medium which can stimulate the growth of the rumen microbiota, but this aspect has never been considered in the past. Their high contribution to ammonia production has bad consequences on the urinary nitrogen excretion but means also that less dietary soluble nitrogen is necessary when protozoa are present. Changes in the molar percentages of VFA and gases from rumen fermentations are not so large that they could alter significantly the use of energy by animals. The answer of animals to elimination of protozoa (defaunation) depends on the balance between energy and protein needs of animals and the supply of nutrients supplied through the diet. Defaunation is useful in case of diets short in protein nitrogen but not limited in energy supply for animals having high needs of proteins.


Rumen Protozoa;Carbohydrate Digestion;Protein Digestion;Ecosystem;Fermentation;Review

Cited by

  1. Sociobiology of biodegradation and the role of predatory protozoa in biodegrading communities vol.32, pp.4, 2007,
  2. Effect of defaunation on body conformation changes, wool yield and fibre characteristics of growing lambs in a hot semiarid environment vol.47, pp.7, 2007,
  3. Efficiency of monolaurin in mitigating ruminal methanogenesis and modifying C-isotope fractionation when incubating diets composed of either C3 or C4 plants in a rumen simulation technique (Rusitec) system vol.102, pp.09, 2009,
  4. The role of pH on the survival of rumen protozoa in steers vol.39, pp.10, 2010,
  5. Review on Mycotoxin Issues in Ruminants: Occurrence in Forages, Effects of Mycotoxin Ingestion on Health Status and Animal Performance and Practical Strategies to Counteract Their Negative Effects vol.7, pp.8, 2015,
  6. Technical note: A method for isolating glycogen granules from ruminal protozoa for further characterization 1 vol.99, pp.3, 2016,
  7. The Planktonic Core Microbiome and Core Functions in the Cattle Rumen by Next Generation Sequencing vol.9, pp.1664-302X, 2018,
  8. Effect of Linseed Oil Supplementation on Ruminal Digestion in Dairy Cows Fed Diets with Different Forage:Concentrate Ratios vol.86, pp.12, 2003,