HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Interpretive Summary Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Sylvester, J. T. Articles by Firkins, J. L. Search for Related Content PubMed PubMed Citation Articles by Sylvester, J. T. Articles by Firkins, J. L.

Rumen ciliated protozoa decrease generation time and adjust 18S ribosomal DNA copies to adapt to decreased transfer interval, starvation, and monensin¹

J. T. Sylvester^*,, S. K. R. Karnati^*, B. A. Dehority^*,, M. Morrison^*,, G. L. Smith^*, N. R. St-Pierre^* and J. L. Firkins^*,2

^* Department of Animal Sciences, The Ohio State University, Columbus 43210
Current position: Buckeye Nutrition, 330 E. Schultz Ave., Dalton, OH 44618
Ohio Agricultural Research and Development Center, The Ohio State University, Wooster 44691
CSIRO Livestock Industries, Queensland Biosciences Precinct, University of Queensland, 306 Carmody Road, St Lucia, Queensland, Australia 4067

² Corresponding author: firkins.1{at}osu.edu

Defaunation studies have documented decreased ammonia concentrations associated with reduced microbial protein recycling and wastage of dietary protein, whereas many methods to suppress protozoa can reduce feed intake or depress ruminal organic matter or fiber digestibility. Therefore, more research is needed to optimize dietary conditions that improve protozoal growth and ruminal outflow relative to autolysis and recycling. Response in growth rate to ruminal outflow was simulated by abrupt changes in transfer interval of batch cultures, and substrate availability was evaluated by feeding without or with abrupt addition of monensin, which was postulated to inhibit digestive vacuole function. In experiment 1, Entodinium caudatum, a mix of Entodinium species, Epidinium caudatum, or Ophryoscolex caudatus cultures rapidly adjusted their generation times to approach respective changes in transfer interval from 3 to 2 or 1 d (cultures were always fed at 24-h intervals). Monensin (0.25 µM) consistently delayed this response. To evaluate a metabolic upshift associated with feeding or a downshift associated with substrate depletion, experiment 2 used real-time PCR to quantify protozoal 18S rRNA gene (rDNA) copies that were expressed relative to cell numbers or to the cellular constituents N and nucleic acids after feeding without or with monensin (0.5 µM). The 18S rDNA copies per milligram of nucleic acids were least for Ophryoscolex compared with the other cultures. When averaged over cultures (no culture x treatment interaction), 18S rDNA copies per unit of nucleic acids decreased at 16 h when cultures were starved but increased with feeding unless monensin uncoupled availability of consumed substrate. Rumen protozoal growth increased in response to decreased transfer interval in experiment 1. Substrate availability appeared to initiate metabolic responses preparing for cell growth, explaining how cultures could rapidly adjust to decreasing transfer interval in experiment 2. Because feeding was not coupled with transfer in experiment 2, however, a metabolic control probably arrested cell division to prevent overgrowth relative to substrate availability.

Key Words: rumen protozoal growth • protozoal generation time • monensin • protozoal 18S ribosomal DNA copies

This article has been cited by other articles:

				E. R. Oelker, C. Reveneau, and J. L. Firkins Interaction of molasses and monensin in alfalfa hay- or corn silage-based diets on rumen fermentation, total tract digestibility, and milk production by Holstein cows J Dairy Sci, January 1, 2009; 92(1): 270 - 285. [Abstract] [Full Text] [PDF]