title: Rumen metabolism of 22:6n-3 in vitro is dependent on its concentration and inoculum size, but less dependent on substrate carbohydrate composition.
abstract: Ruminal disappearance of linoleic and linolenic acid has been studied extensively. Less is known of the metabolism of docosahexaenoic acid (22:6n-3). The aim of this study was to identify factors which affect the disappearance of 22:6n-3 during in vitro batch incubations using rumen fluid from sheep. In experiment 1, the effect of the rumen fluid/buffer ratio (0.2 or 0.4), substrate (cellulose or cellulose/glucose), time of 22:6n-3 addition (0.08 mg/mL after 0 or 6 h of incubation) and incubation time (24 or 48 h) was evaluated. A mixture design was used in experiment 2 to evaluate the effect of carbohydrate type (cellulose, glucose, cellobiose and starch) on 22:6n-3 disappearance (0.08 mg/mL). In experiment 3, several concentrations of 22:6n-3 (0.05-0.30 mg/mL) were evaluated with different substrate mixtures (combinations of cellobiose, starch and cellulose). In a final experiment, the effect of the rumen fluid/buffer ratio (0.20, 0.35 and 0.50) and substrate (glucose, cellobiose and starch) was evaluated. In this experiment, 22:6n-3 was added as a proportion of rumen fluid ranging from 0.1 to 0.4 mg/mL rumen fluid, contrary to former experiments where concentrations were relative to culture medium. Low levels of 22:6n-3 (0.05 mg/mL) allowed extensive metabolism whereas increasing amounts of 22:6n-3 hampered its disappearance. A greater proportion of rumen fluid resulted in increased disappearance of 22:6n-3. The effect of carbohydrate type was small compared with the former two factors. These results suggest that in vitro metabolism of 22:6n-3 is mostly dictated by the conditions at the start of the incubation, i.e., inoculum, probably reflecting the density of bacteria able to metabolize 22:6n-3.
authors.affiliation: Laboratory for Animal Nutrition and Animal Product Quality, Ghent University, Proefhoevestraat 10, 9090, Melle, Belgium, bruno.vlaeminck@ugent.be.
authors.forename: B
authors.initials: B
authors.lastname: Vlaeminck
authors.forename: T
authors.initials: T
authors.lastname: Braeckman
authors.forename: V
authors.initials: V
authors.lastname: Fievez
mesh_terms: D000818:Animals; D002482:Cellulose / Q000737:chemistry; D005750:Gastric Juice / Q000737:chemistry; D006865:Hydrogenation; D019787:Linoleic Acid / Q000737:chemistry*; D050356:Lipid Metabolism; D012417:Rumen / Q000378:metabolism*; D034561:Sheep, Domestic; D012996:Solutions; D017962:alpha-Linolenic Acid / Q000737:chemistry*
chemical_list: D012996:Solutions; D017962:alpha-Linolenic Acid; D002482:Cellulose; D019787:Linoleic Acid
references.citation: J Dairy Sci. 2004 Apr;87(4):1047-50
references.pmid: 15259240
references.citation: Lipids. 2008 Mar;43(3):259-73
references.pmid: 18214567
references.citation: J Dairy Sci. 2008 Mar;91(3):1122-32
references.pmid: 18292268
references.citation: Mol Syst Biol. 2012;8:617
references.pmid: 23047527
references.citation: Br J Nutr. 2006 Jun;95(6):1199-211
references.pmid: 16768845
references.citation: J Dairy Sci. 2011 Sep;94(9):4676-83
references.pmid: 21854940
references.citation: J Anim Sci. 2008 Feb;86(2):397-412
references.pmid: 18042812
references.citation: Benef Microbes. 2013 Dec 1;4(4):299-312
references.pmid: 24311313
references.citation: BMC Microbiol. 2010 Feb 18;10:52
references.pmid: 20167098
references.citation: Lipids. 2011 Jul;46(7):587-606
references.pmid: 21562931
references.citation: J Dairy Sci. 2004 Mar;87(3):645-51
references.pmid: 15202649
references.citation: J Exp Med. 1947 Jan 1;85(1):9-22
references.pmid: 19871602
references.citation: Appl Environ Microbiol. 2000 Dec;66(12):5226-30
references.pmid: 11097894
references.citation: Animal. 2010 Sep;4(9):1528-40
references.pmid: 22444700
references.citation: Antonie Van Leeuwenhoek. 2007 May;91(4):303-14
references.pmid: 17072533
references.citation: J Nutr. 2012 Aug;142(8):1437-48
references.pmid: 22739367
references.citation: Biotechnol Bioeng. 1999;66(4):203-10
references.pmid: 10578090
references.citation: Appl Microbiol Biotechnol. 2010 Feb;85(6):1629-42
references.pmid: 19956944
references.citation: Lipids. 2012 Aug;47(8):821-5
references.pmid: 22695744