Biohydrogenation kinetics of oleic, linoleic and alpha-linolenic acids in vivo

Abstract Text: Biohydrogenation (BH) of unsaturated fatty acids (FA) has been extensively studied in vitro; however, in vitro BH rates and extents may not parallel BH pathways in vivo.  The objective was to assess rate and extend of oleic (OA), linoleic (LA) and alpha-linolenic acid (ALA) biohydrogenation in vivo.  Each FA was characterized in a separate experiment (EXP.1 – oleic, EXP.2 – linoleic, and EXP.3 – alpha-linolenic) using 4 ruminally cannulated lactating Holstein cows in each experiment.  A single bolus consisting of 200 g of an oilseed (EXP.1 87% OA sunflower, EXP.2 70% LA safflower, and EXP.3 54% ALA flaxseed) and 12 g of heptadecanoic acid (17:0) was mixed with rumen contents.  Rumen digesta was collected at -1, -0.25, 0.1, 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4, and 6 h relative to the bolus.  Samples were immediately placed on dry ice, stored at -20^oC, freeze-dried, methylated and analyzed by GC-FID.  On the day of infusion, cows were fed at a rate of 4.2%/h of expected daily DMI.  The geometric mean of the 4 cows was calculated and the disappearance of 17:0, OA, LA, and ALA was fit to a single exponential decay model using the nonlinear procedure of JMP Pro.  Overall, the boluses increased total fat in the rumen from 4.1 to 7.4% and enriched 17:0 from 0.4 to 2.5% of FA. The bolus enriched OA from 9.0 to 30.1% of FA in EXP. 1, LA from 12.5 to 35.9% of FA in EXP.2, and ALA from 1.9 to 19.8% of FA in EXP.3.  The fractional rate of 17:0 disappearance was 10.9, 8.5, and 6.7%/h in EXP.1, 2 and 3, respectively, and was used as a marker of FA passage.  The fractional rate of disappearance of OA was 55%/h, LA was 61.2%/h, and ALA was 93.9%/h in EXP.1, 2 and 3, respectively, and all three unsaturated FA reached pre-bolus concentration within 4 h.  Based on kd/(kd+kp), the extent of BH was 83.4% for OA, 87.8% for LA, and 93.3% for ALA in EXP.1, 2 and 3, respectively.  Assuming that BH equals disappearance minus passage, the BH rates were 44.0, 52.7, and 87.1%/h for OA, LA, and ALA in EXP.1, 2 and 3, respectively.  In conclusion, the extent of oleic, linoleic, and alpha-linolenic biohydrogenation was near expected values, but the rate of ruminal biohydrogenation was higher than that commonly observed in vitro for these three unsaturated FA. 

Keywords: rumen, biohydrogenation