390 Effects of dietary-induced pH changes on feed digestion, nitrogen metabolism, fermentation, and biohydrogenation of polyunsaturated fatty acids in dual-flow continuous culture fermenters

Abstract

Abstract Ruminal pH decreases as greater concentrations of grain are consumed, and as a result, reduces biohydrogenation of polyunsaturated fatty-acids. Our objective was to investigate effects of diet on pH and biohydrogenation activity in vitro. Eight dual-flow, continuous culture fermenters were blocked by side of the room and randomly assigned, within block, to 1 of 4 treatments. Treatments consisted of 100:0 roughage-to-concentrate (Grass), 50:50 roughage-to-concentrate plus flax oil supplement (Mix+F), 10:90 roughage-to-concentrate plus corn oil supplement (Con+C), or 10:90 roughage-to-concentrate plus flax oil supplement (Con+F). Fermenter pH, area under the curve, and maximum pH were lowest for Con+C and Con+F (P < 0.05). Apparent and true DM, OM, and NDF digestibility were greater with grain inclusion (P < 0.05) while ADF digestibility was not affected by treatment (P > 0.10). Protein degradation was lowered as grain inclusion increased (P < 0.05). Total VFA concentrations were lowest for Grass, highest for Con+C and Con+F, and intermediate for Mix+F (P < 0.05). Acetate-to-propionate was lowest for Con treatments (P < 0.05). Biohydrogenation of 18:2n-6 and 18:3n-3 fatty-acids were reduced (P < 0.01) with inclusion of concentrate regardless of roughage-to-concentrate ratio. Concentrations of stearic acid recovered from effluent were greatest for Grass, intermediate for Mix+F, and lowest for both Con+C and Con+F (P < 0.05). Linoleic acid proportions in effluent were greatest for Con+C and Con+F and intermediate for Mix+F (P < 0.05), and inclusion of concentrate, regardless of amount, increased the amount linoleic acid recovered from fermenter overflow (P < 0.01). Between Con+C and Con+F concentrations of alpha-linolenic acid (ALA) was greater when flax oil was supplemented (P < 0.01). Proportions of ALA in effluent was similar (P > 0.10) between Grass and Con+C; however, between Mix+F and Con+F ALA concentrations tended (P = 0.06) to be greater for Con+F. Omega6-to-omega3 ratios were similar across Grass, Mix+F, and Con+F (P > 0.10) and greatest for Con+C (P < 0.05).