Submitted to: Journal Dairy Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: August 28, 1998
Publication Date: N/A
Technical Abstract: The purpose of this study was to determine if individual fibrolytic species were differentially affected by diet. Four cows were used in a balanced 4 x 4 Latin square design with factorial arrangement of treatments (2 fiber sources and 2 fiber levels). Diets containing alfalfa silage or corn silage with either 24 or 32% aNDF (using sodium sulfite and amylase) were fed at 12 h intervals during 4-week periods. After dietary adaptation (23 d), the relative population sizes of Fibrobacter succinogenes, Ruminococcus flavefaciens and R. albus were determined from ruminal samples collected 3 h post-feeding over 3-5 feeding cycles. Population sizes were determined using oligonucleotide probes to species-specific 16S ribosomal RNAs, and were calculated as a fraction of total bacterial RNA. R. albus was the most abundant of the three species, accounting for up to 3% of the bacterial population. The other two species each typically accounted for <1% of the population. Relationships among cow, diet, and microbial population were obscured somewhat by the inherently high variability of the RNA probe method. However, analysis of variance revealed that the effects of diet on the populations were not significant (p<0.05), while differences among cows were noted for some populations. The relative population size of each species was positively correlated (P<0.05) with one another, and R. albus populations were positively correlated with milk production (P<0.05). The data suggest that populations of these three fibrolytic species respond coordinately, and that population levels of individual species are more dependent on cow than on diet.