Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/2007
Publication Date: 7/1/2007
Citation: Trabue, S.L., Scoggin, K.D., Tjandrakusma, S., Rasmussen, M.A., Reilly, P.J. 2007. Ruminal fermentation of propylene glycol and glycerol. Journal of Agricultural and Food Chemistry. 55:7043-7051. Interpretive Summary: The feeding of sugars and other hydroxylated organics to ruminants for either therapeutic or environmental purposes are of long standing. Propylene glycol has been fed to early postpartum dairy cows to prevent ketosis. However, high doses of propylene glycol have been shown to result in production of malodorous compounds. Rumen fluid was treated with propylene glycol and glycerol. After 24 h of incubation, propylene glycol was completed, metabolized, whereas, glycerol alone was only 80% metabolized. The addition of all substrate resulted in increased levels of acetate, propionate, butyrate, valerate and caproate. The addition of propylene glycol increased propionate but decreased butyrate formation, while glycerol increased valerate and caproate and small amount of lactate. Metabolism of propylene glycol led to the production of malodor compounds with 10 being identified a significant contributor to the malodor. Research results described in this report provides animal scientists, veterinarians and biodiesel industry representatives' valuable information on the metabolism of glycerol and propylene glycol in rumen fluid and identified volatile odorous compounds emitted from ruminates treated with these compounds.
Technical Abstract: Bovine rumen fluid was fermented anaerobically with 25 mM R-propylene glycol, S-propylene glycol, or glycerol added. After 24 h all of the propylene glycol enantiomers and approximately 80% of the glycerol were metabolized. Acetate, propionate, butyrate, valerate, and caproate concentrations, in decreasing order, all increased with incubation time. Addition of any of the three substrates somewhat decreased acetate formation, while addition of either propylene glycol increased propionate formation but decreased that of butyrate. R- and S-propylene glycol did not differ significantly in either their rates of disappearance or in the products formed when they were added to the fermentation medium. Fermentations of rumen fluid containing propylene glycol emitted the sulfur-containing gases 1-propanethiol, 1-(methylthio)propane, methylthiirane, 2, 4-dimethylthiophene, 1-(methylthio)-1-propanethiol, dipropyl disulfide, 1-(propylthio)-1-propanethiol, dipropyl trisulfide, 3,5-diethyl-1,2,4-trithiolane, 2-ethyl-1,3-dithiane, and 2,4,6-triethyl-1,3,5-trithiane. Metabolic pathways that yield each of these gases are proposed. The sulfur-containing gases produced during propylene glycol fermentation in the rumen may contribute to the toxic effects seen in cattle when high doses are administered for therapeutic purposes.