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Abstract: Effects of a docosahexaenoic acid (DHA)-edible algae product, Aquagrow-DHA, on lipolysis and biohydrogenation of linoleic acid (C18:2 n-6) was studied in 24h in vitro incubations with buffer (20ml), sheep rumen contents (5ml), hay (0.4g) and sunflower oil (20mg). Four Aquagrow-DHA levels (0, 20.8, 41.6, 83.3mg) were tested and addition of lard ensured that the total fat content was constant. Increasing Aquagrow-DHA proportionally inhibited hydrogenation of C18:2 n-6, provoking an accumulation of C18:1 trans fatty acids (mainly C18:1 t10+t11). Analogous incubations for 6 and 24h with linseed oil (20mg) instead of sunflower oil, resulted in the accumulation of C18:2 t11c15 and, to a lower extent, C18:1 t10+t11 and showed that Aquagrow-DHA reduced the rate of lipolysis of linolenic acid (C18:3 n-3). Comparison of these results with incubations with the individual constituents of Aquagrow-DHA and whole algae biomass revealed that the observed effects were related to the presence of DHA. Finally, incubations under a 50:50 H2:CO2 atmosphere suggested a direct inhibitory effect of unesterified DHA on hydrogenating bacteria involved in the conversion of C18:2 t11c15 and C18:1 trans isomers, rather than on H2 availability. [Copyright &y& Elsevier]

Abstract: In 24h in vitro incubations with 25ml of buffered rumen fluid, four doses (0, 20.8, 41.6 and 83.3mg) of a DHA-edible algae product, Aquagrow-DHA, were examined in combination with sunflower (20mg) or linseed oil (20mg). One treatment contained no Aquagrow-DHA, linseed or sunflower oil and one was supplemented with Aquagrow-DHA (166.6mg) only. Addition of lard ensured that total fat content was constant among incubations. Increasing amounts of Aquagrow-DHA progressively inhibited CH4 to a maximum of 80% (P<0.001). Increased CH4 inhibition was accompanied by decreased acetate (P<0.001) and butyrate (P<0.001), and increased propionate (P<0.001) proportions, but also by depression of the short chain fatty acid (SCFA) production by 30% at the highest Aquagrow-DHA level (P<0.001). However, SCFA inhibition only occurred when the Aquagrow-DHA dose exceeded 41.6mg and CH4 production was reduced by about 30% (P<0.05) at this dose. Inhibitory effects were linked to the amount of unesterified polyunsaturated fatty acids, particularly docosahexaenoic acid. Incubations under partial H2 atmosphere suggested that a direct toxic effect to rumen methanogens was caused by higher amounts of unesterified DHA (>41.6mgAquagrow-DHA/incubation) only, whereas suppression of rumen methanogenesis at lower doses seemed to be indirect through a lack of substrate. This indicates bacteria providing H2 to the rumen methanogens to be more sensitive to unesterified DHA than rumen methanogens. [Copyright &y& Elsevier]

Abstract: Previously, combining docosahexaenoic acid (DHA) with linoleic acid in rumen cultures enhanced vaccenic acid (VA) and conjugated linoleic acid (CLA) accumulations. The objective of this experiment was to examine the effect of two pH levels and two polyunsaturated C18 fatty acid (FA) sources on VA and CLA accumulations in rumen cultures incubated with DHA. High pH culture treatments consisted of 10mg DHA+20mg linoleic acid (LOH), or 10mg DHA+20mg linolenic acid (LNH). Low pH culture treatments consisted of 10mg DHA+20mg linoleic acid (LOL), or 10mg DHA+20mg linolenic acid (LNL). Treatments were incubated in triplicate in 125ml flasks containing 500mg finely ground TMR, 10ml strained ruminal fluid, 40ml media, and 2ml reducing solution. Ruminal fluid was collected from fermenters fed high forage (pH 6.7) or high grain diets (pH 5.4). A 5-ml sample of culture contents was taken at 0 and 24h for fatty acid analysis by gas liquid chromatography. After 24h of incubation, VA was the predominant trans C18:1 FA isomer in the high pH cultures and its concentration was greater with LOH (20.9mg/culture) than with LNH (9.3mg/culture). Similarly, t10 C18:1 was the predominant trans C18:1 FA isomer in the low pH cultures and its concentration was greater with LOL (12.8mg/culture) than with LNL (4.5mg/culture). The c9t11 CLA (0.74mg/culture) and tt CLA (0.67mg/culture) were the predominant CLA isomers in the LOH cultures, while t10c12 CLA (1.47mg/culture) and tt CLA (1.27mg/culture) were the predominant CLA isomers in the LOL cultures. The t11t13 CLA increased in linolenic acid cultures, particularly when linolenic acid incubated under low pH condition (0.95mg/culture). Additions of linolenic acid to rumen cultures caused a dramatic increase in the concentration of t11c15 C18:2 (9.84 and 8.45mg/culture, for treatments LNH and LNL, respectively). The concentrations of VA and c9t11 CLA in rumen cultures were greatest when DHA was incubated with linoleic acid at high pH. In contrast, t10 C18:1 replaced VA and c9t11 CLA disappeared when linoleic and linolenic acids were incubated under the low pH condition. This study shows that the best approach to increase ruminal VA production, and potentially c9t11 CLA levels in ruminant food products, is by combining a DHA source (such as fish oil or algae) and linoleic acid source under high ruminal pH condition. [Copyright &y& Elsevier]