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ARS Home » Midwest Area » Lexington, Kentucky » Forage-animal Production Research » Research » Publications at this Location » Publication #310664

Title: Hops (Humulus lupulus) ß-acid as an inhibitor of caprine rumen hyper-ammonia-producing bacteria in vitro

item Flythe, Michael
item Aiken, Glen
item Gellin, Gloria
item Klotz, James
item GOFF, BEN - University Of Kentucky
item ANDRIES, KENNETH - Kentucky State University

Submitted to: Agriculture, Food and Analytical Bacteriology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/5/2015
Publication Date: 6/1/2015
Citation: Flythe, M.D., Aiken, G.E., Gellin, G.L., Klotz, J.L., Goff, B.M., Andries, K. 2015. Hops (Humulus lupulus) ß-acid as an inhibitor of caprine rumen hyper-ammonia-producing bacteria in vitro. Agriculture, Food and Analytical Bacteriology. 5:29-36.

Interpretive Summary: A symbiotic relationship with the rumen microflora (bacteria and other microorganisms) is the adaptation that allows goats and other ruminants to digest plant fiber. The microorganisms also digest plant protein. Protein degradation is not inherently harmful to ruminants, but some of the resulting amino acids are converted to ammonia. Excess ammonia is wasted and can become a pollutant. Much of the ammonia production from the resulting peptides and amino acids is attributable to a group of bacteria that have been termed Hyper Ammonia-producing Bacteria, HAP or HAB. The activity of HAB can be reduced by ionophores feed additives, which decrease waste ammonia and make feeding more efficient. This study evaluated the ability of a plant-based compound to reduce ammonia production by HAB from the goat rumen. The compound, commonly called beta-acid, is a fragrant, bitter component of the hops plant that is known to selectively stop the growth of certain bacteria. The beta-acid decreased the degradation of amino acids to ammonia by wild microorganisms from the goat rumen. It also prevented the growth of pure cultures of known goat HAB in the laboratory. These results suggest that hops or hops beta-acids could be useful in controlling wasteful ammonia production in the goat rumen.

Technical Abstract: Antimicrobial plant secondary metabolites increase rumen efficiency and decrease waste products (i.e. ammonia, methane) in some cases. A promising source of bioactive secondary metabolites is the hops plant (Humulus lupulus L.), which produces '-acid, a suite of structurally similar, potent antibacterial compounds. The efficacy of hops has been shown in bovines. Additionally, the '-acid mechanism of antimicrobial action determined on rumen bacteria of bovine origin. The objective of the current study was to determine the effect of hops '-acid on amino acid degradation and ammonia production by goat rumen bacteria. The growth of two rumen hyper-ammonia-producing bacteria of caprine origin (Peptostreptococcus spp. BG1 and BG2) was inhibited by '-acid (= 45 ppm and = 4.5 ppm, respectively) when either amino acids or peptides were the growth substrate. Uncultivated, mixed rumen microorganisms harvested from goats produced approximately 35 mM ammonia from amino acids and 50 mM ammonia from peptides during 24 h incubation. The addition of '-acid reduced the ammonia concentration, and there was a dose-response relationship between the '-acid concentration and the ammonia concentration. Peptide catabolism was more sensitive than free amino acid catabolism to '-acid inhibition because as little as 3 ppm resulted in less ammonia than the control (P < 0.05). These results show that hops '-acid is effective against caprine HAB and suggest that hops could be useful in controlling wasteful metabolic processes in the caprine rumen.