and Nutrient-Nutrient Interactions The Production of 10-Hydroxystearic and 10-Ketostearic Acids Is an Alternative Route of Oleic Acid Transformation by the Ruminal Microbiota in Cattle

The formation of hydroxystearic acid (HSA) and ketostearic acid (KSA) from oleic acid transformation has been documented in a variety of microbial species, including several isolated from the rumen of domesticated ruminant species. However, their ruminal production rates have not been established as inﬂuenced by fatty acid source. Dosing continuous cultures of mixed ruminal microorganisms with 1- 13 C-oleic acid increased the 13 C enrichment of both HSA and KSA at 24 h postdosing, and showed that the majority (96 and 85%, respectively) of the HSA and KSA present in the 24-h samples originated from oleic acid. Several experiments using batch cultures of ruminal microorganisms showed that production of HSA and KSA was directly related to oleic acid input but was not affected by elaidic acid input, and that HSA was further metabolized to KSA but not to other fatty acids. When continuous cultures of ruminal microorganisms were supplemented with soybean oil or canola oil, production of 10-HSA 1 10-KSA was related to oleic acid input but not to linoleic acid input. Daily production of 10-HSA 1 10-KSA across treatments was 14.4 m mol/100 m mol oleic acid input into the cultures or 31.1 m mol/100 m mol oleic acid net loss. The results of this study quantify the formation of 10-HSA and 10-KSA from oleic acid transformation by ruminal microorganisms, and show that their accumulation in ruminal contents is directly related to the extent of oleic acid input and biotransformation by the rumen microbiota. J. Nutr. 136: 926–931, 2006. of 10-HSA and 10-KSA. Isotope experiment. Details of fermenter speciﬁcations and isotope dosing were described previously (11). Brieﬂy, 4 dual-ﬂow continuous culture vessels were used in a 4 3 4 Latin square with 10-d periods to evaluate 2 pH (5.5 and 6.5) and 2 liquid dilution rates (0.05 and 0.10 h (cid:2) 1 ) arranged factorially. Data were averaged across treatments in this study to determine the overall transfer of oleic acid carbons to HSA and KSA across all conditions. A total of 22 g of feed (55% alfalfa pellets and 45% concentrate, DM basis) was introduced daily into the fermenters in 2 equal amounts at 0830 and 1630 h. Diets contained 29 g/kg added oleic acid with an additional 885 m mol of oleic acid in 5 mL of ethanol injected directly into each fermenter on d 1–9 just after the morning feeding. On d 10, 885 m mol of 1- 13 C-oleic acid replaced the unlabeled oleic acid in the 5 mL injection. Samples of mixed culture contents were taken at 0 h (just before injection of the stable isotope) and again at 24 h after injection of the isotope. Samples were imme-diately stored at (cid:2) 5 8 C. Production experiment. Fermentors were modiﬁed slightly from the design described by Teather and Sauer (10) to include a sidearm that angled downward rather than straight out to allow for greater gravitational pull on overﬂow contents and minimize clogging at higher feeding rates. As a result of this modiﬁcation, feed was introduced into fermenters at 60 g/d without evidence of clogging. Diets consisted of 500 g/kg alfalfa pellets and 500 g/kg concentrate and contained either 1 ) no added lipid (control), 2 ) 50 g/kg soybean oil (SBO), or 3 ) 50 g/kg canola oil (CO). Ingredients in the control concentrate (g/kg) were: 375 ground corn, 100 soybean meal, 12.2 CaHPO