Inhibition of Growth and Ammonia Production of Ruminal Hyper Ammonia-Producing Bacteria by Chinook or Galena Hops after Long-Term Storage

Surplus hops (Humulus lupulus L.) that are not needed by the brewing industry could be used as a feed supplement for cattle and other ruminants. Previous research indicates that antimicrobial hops plant secondary metabolites (i.e., αand β-acids) inhibit methane and ammonia production and promote the growth of ruminant animals. The goal was to determine that hop pellets produced for brewing still possessed the requisite antimicrobial activity after 5-year storage. HPLC (high performance liquid chromatography) analysis indicated that the αand β-acid concentrations in two varieties of hops were relatively stable after 5 years of storage under N2. Either hop variety inhibited the growth of the ruminal hyper ammonia-producing bacterium, Clostridium sticklandii SR, in broth culture and Petri plate bioassays. Either hop variety inhibited ammonia production from amino acids or peptides by mixed rumen microorganisms from Holstein steers. These results are similar to those previously obtained with fresh hops, hops extracts, other antimicrobial phytochemicals and typical feed ionophores, such as monensin. The rumen-active antimicrobial phytochemicals in hops can still be present and active after years under certain storage conditions. Further investigation is warranted to determine how surplus and older hops can be used to benefit ruminant nutrition and ruminant industries.