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Post-Prandial Compositional Changes of Fluid- and Particle-Associated Ruminal Microorganisms¹

Louisiana State University Agricultural Center Baton Rouge 70803 and United States Department of Agriculture Madison, WI 53706

Abstract

Two ruminally cannulated cows were fed a diet containing 65% alfalfa haylage and 35% concentrate every 12 h. During two collection periods, whole ruminal contents were sampled before feeding, when feed not eaten was removed (1 h after initiation of feeding) and 1, 2, 3, 4, 6, 8, 10 and 12 h after removal. At each sampling, fluid-associated microorganisms were obtained by straining whole ruminal contents through eight layers of cheesecloth. A portion of the particle-associated population was obtained by chilling squeezed particles before seven successive extractions with saline solution. Microbial ash concentrations ranged from 9.9 to 16.6% of dry matter, with differences due to population (P<.01) and to time after feeding for both fluid- (P<.05) and particle-associated (P<.01) microorganisms. Within 1 h after initiation of feeding, N decreased (P<.05) from a pre-feeding concentration of 9.5% of organic matter to 7.7% for fluid-associated microorganisms, and from 9.2 to 6.7% for particle-associated microorganisms. Both populations did not return to pre-feeding concentrations until 6 h after feed removal. Nucleic acid concentrations decreased (P<.05) in both populations after feeding, and did not return to pre-feeding concentrations until 6 h for fluid-associated and 4 h for particle-associated microorganisms. Nucleic acid-to-N ratios were higher (P<.01) in the fluid- than particle-associated organisms. Decreases (P<.01) in lipid concentrations due to feeding were observed only in the particle-associated fraction. Mean lipid concentration of particle-associated microorganisms was 22.4% of organic matter compared with 24.2% for fluid-associated microorganisms. Polysaccharide concentrations increased after feeding and remained higher (P<.05) until 6 h after feed removal for both populations. Peak polysaccharide concentrations were obtained 1 h after feed removal, and were 20.3% of organic matter for fluid-associated and 33.6% for particle-associated microorganisms. Results are interpreted to indicate that when studying chemical composition of ruminal microorganisms, measurements should be made on both fluid- and particle-associated microorganisms.

¹ A portion of these data was presented at the VI Int. Symp. on Ruminant Physiology, Banff, Alberta, Canada, 1984.

² Dept. of Anim. Sci., Louisiana State Univ.

³ Present address: Dept. of Anim. Sci., Univ. of Arizona, Tucson 85721.

⁴ U.S. Dairy Forage Res. Center, USDA-ARS, Univ. of Wisconsin, Madison 53706.

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