J. Anim Sci.
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J. Anim Sci. 1974. 38:865-870.
© 1974 American Society of Animal Science
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Rumen Fluid Osmolality: Evaluation of Its Influence upon the Occurrence and Numbers of Holotrich Protozoa in Sheep1

B. A. Dehority and J. R. Males2

Ohio Agricultural Research and Development Center,3, Wooster 44691

Abstract

The osmotic pressure of rumen fluid was investigated as a possible factor influencing the occurrence and numbers of rumen holotrich protozoa in sheep. Fasting osmotic pressures, measured just prior to the daily feeding, ranged from 224 to 270, mOsmoles/kg, while holotrich numbers varied between 0 and 32.4 x 103/cm3 of rumen contents. These two variables were not correlated (r = 0.17). Correlations between holotrich numbers just prior to feeding and osmotic pressure at varying times after feeding were inconsistent between trials, ranging from –.72 to 0.90. Restricting feed intake tended to lower both osmolality and holotrich numbers. Inoculation with rumen contents containing both Isotricha and Dasytricha, while on restricted feed intake, allowed establishment of both genera in all animals. When the sheep were returned to the normal feed level, both osmolality and holotrich numbers increased markedly. Fasting osmotic pressure increased significantly during water restriction; however, except for a temporary initial increase in rumen fluid osmolality after feeding, results of the water restriction experiment were quite similar to those for feed restriction. Withholding water for 27 hr. increased the average fasting osmolality from 246 to 298 mOsmoles/kg and the osmolality 11/2 hr. after feeding from 393 to 416 mOsmoles/kg. Total holotrich numbers were determined 24, 96 and 168 hr. after the start of the experiment, and remained quite constant throughout. Within both the normal ranges of osmotic pressure and extremes caused by manipulation of feed and water intake, this parameter does not appear to be associated with the occurrence or numbers of holotrich protozoa.

Footnotes

1 Approved for publication as Journal Article No. 83-73 by the Associate Director of the Ohio Agricultural Research and Development Center.

2 Present address: Department of Animal Sciences and Industry, Oklahoma State University, Stillwater 74074.

3 Department of Animal Science.






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Copyright © 1974 by the American Society of Animal Science.