Volume 89, Issue 1, January (2003), pp. 97-103 © The Author 2003
doi:10.1079/BJN2002752

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Effects of feed intake on composition of sheep rumen contents and their microbial population size

C. A. Rodríguez^1*, J. González¹, M. R. Alvir¹, R. Redondo² and C. Cajarville^1>†
1Departamento de Producción Animal, Universidad Politécnica de Madrid, 28040 Madrid, Spain
²Servicio Interdepartamental de Investigación, Universidad Autónoma de Madrid, 28049 Madrid, Spain

 (Received 8 November 2001–Revised 6 August 2002–Accepted 6 September 2002)

The present study was conducted to determine the effect of feed intake on the composition of the rumen contents of sheep and on their bacterial densities. Whole rumen contents were sampled after a period of continuous inter-rumen infusion of ¹⁵NH₃ from four rumen-cannulated wethers successively fed on a hay–concentrate diet (2:1, w/w on a DM basis) at two rates of feed intake: 40 and 80 g DM/kg body weight^0·75. Total weight and chemical composition of rumen contents, as well as the distribution by size and chemical composition of particles, were determined. The populations of bacteria associated with the liquid (liquid-associated bacteria, LAB) and solid (solid-associated bacteria, SAB) fractions of rumen digesta and the distribution of SAB according to feed particle size were also examined. The greater feed intake caused an increase in the mass of the rumen contents, while its chemical composition did not change, except for a higher content of organic matter (P=0·023). The distribution of feed particles by size was similar at both levels of intake. The concentrations of neutral- and acid-detergent fibre in feed particles decreased and those of total, dietary, and microbial N increased, both with a quadratic response (P=0·001), as particle size decreased. The proportion of LAB in the microbial biomass of rumen digesta reached only 8·0 %. This proportion and the density of LAB were unaffected by the level of feed intake, whereas an apparent reduction (10·4 %) occurred with the SAB biomass in whole rumen contents. A systematic, but not significant, reduction (mean value 11·9 %) in the level of microbial colonisation in the different particle fractions with the increase of feed intake was also observed.

*Corresponding author: Dr C. A. Rodríguez, fax +34 91 5499763, email crodriguez@pan.etsia.upm.es
†Present address: Departamento de Nutricio´n Animal, Universidad de la Republica Oriental del Uruguay, 11600 Montevideo, Uruguay.

Keywords:
Rumen contents: Chemical composition: Feed intake: Microbial population size