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Impact of palmitic acid and pH on ruminal NDF digestibility and fermentation in a continuous culture system.

L. Padilla


Impact of palmitic acid and pH on ruminal NDF digestibility and fermentation in a continuous culture system.
L. Padilla*, A. Sears, F. Batistel. Department of Animal, Dairy and Veterinary Sciences, Utah State University Logan, UT.

Non-rumen bacteria incorporate exogenous long-chain saturated fatty acids to change membrane fluidity under low pH conditions. We hypothesized that rumen bacteria use a similar mechanism, thus, providing saturated fatty acids in the diet could support bacterial metabolism and growth and consequently enhance fiber digestibility. The objective of this study was to evaluate the effects of dietary palmitic acid and pH on ruminal NDF digestibility and fermentation. The study was conducted as a 2 � 2 factorial treatment arrangement in a replicated 4 � 4 Latin square using continuous culture fermenters (n = 8). Treatments were a control diet without supplemental fatty acids or the control diet plus 1.5% of palmitic acid factorialized with normal pH (diurnally ranging from 6.4 to 7.0) or low pH (diurnally ranging from 6.0 to 6.4). The control diet (40 g DM/day) was a 50:50 orchardgrass hay:concentrate mixture that provided 5.8 g CP, 14 g NDF, 7.3 g starch, and 1 g fatty acids fed twice daily. The fatty acid treatment maintained the same nutrient input into the fermenters as the control except for fatty acids. Both buffer solutions (normal and low pH) were delivered continuously at rate of 10%/h. Data were analyzed using a mixed model including the fixed effect of pH, fatty acid, and its interaction, and the random effects of period and fermenter. Data are reported as least squares means with differences declared at P ≤ 0.05. No interaction between fatty acids and pH were observed for the variables measured. Compared with control, palmitic acid increased NDF digestibility (45.2 vs. 39.34%, P = 0.03). The lower pH decreased NDF digestibility in 8.2 percentage units compared with normal pH (46.4 vs. 38.16%, P < 0.01). Furthermore, low pH decreased ammonia (7.30 vs. 5.64 mg/dL, P = 0.01) and total VFA concentration (168 vs. 138 mmol/d, P = 0.02) compared with normal pH; palmitic acid did not (P > 0.10) affect ammonia nor total VFA concentration. Our preliminary data indicate that rumen pH and palmitic acid independently affect NDF digestibility and rumen fermentation. Palmitic acid supplementation increased ruminal fiber digestibility under low and normal pH conditions.

Keywords: fatty acids, rumen, pH.