Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: April 10, 2012
Publication Date: July 15, 2012
Citation: Mohammed, R., Brink, G.E., Stevenson, D.M., Beauchemin, K.A., Weimer, P.J. 2012. Orchardgrass forage effects on bacterial communities and long-chain fatty acid profiles in the rumen of Holstein heifers [abstract]. Journal of Dairy Science. 95(suppl 2):614. Technical Abstract: The aim of this study was to determine if ruminal bacterial community composition (BCC) and long-chain fatty acid (FA) profiles differed in heifers grazing in orchardgrass pasture (OP) versus those fed hay (OH) harvested from the same field at the same stage of maturity. Five ruminally cannulated Holstein heifers (age: 17.0 +/- 0.89 months) were allotted to OP or OH in three 28-d periods. Three of these heifers were offered OP, OH, and OP successively in the 3 periods while the other 2 heifers remained on OP for all periods. Ruminal digesta were collected on three consecutive days near the end of each period. Microbial DNA was extracted from solid and liquid phases of digesta, amplified by PCR using domain-level bacterial primers, and subjected to automated ribosomal intergenic spacer analysis (ARISA). Total ruminal volatile fatty acids (mM) and acetate (mol/100 mol) were greater for OH than for OP, while butyrate was less. The ARISA profiles for the OP and OH diets formed distinct clusters, indicating that ruminal BCC was affected by diet. Branched-chain FA (% total FA methyl esters) in rumen digesta (13:0 anteiso, 14:0 iso, 15:0 iso, 15:0 anteiso and 18:0 iso) were greater for OH than OP. Total trans(t)-18:1, t11-, and t10-18:1 were greater for OP than OH. Conjugated linoleic acid (CLA) isomers (c9, t11-CLA and t10, c12-CLA) were not influenced by the diets. Relative population size (RPS) of Butyrivibrio fibrisolvens and Megasphaera elsdenii in the liquid phase of rumen digesta (fraction of total 16S rRNA gene copy number) were not affected by diet. Regression analysis of ruminal t10-18:1 and RPS of M. elsdenii was not significant. Unexpectedly, the relationship between ruminal t11-18:1 and RPS of B. fibrisolvens was negative (R2 = 0.52; P = 0.04), suggesting that there are likely yet unidentified polyunsaturated FA biohydrogenating rumen bacteria. The differences in ruminal chemistry and BCC in heifers fed OP and OH reflect possible alterations in substrate availability to the rumen microflora due to differences in the form of diet (fresh vs. conserved forage).