Methane and ammonia production in rumen fluid treated with spent brewer’s yeast.


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Virginia Pszczolkowski
Committee: Langdon Martin, Dana Emmert, Steve Cartier

Hop acids from the hops used in brewing beer primarily end up in the yeast once brewing is completed, and have antimicrobial activity against Gram-positive bacteria. Unlike multinational breweries, craft breweries do not produce enough yeast to make processing the yeast into a nutritional supplement to be economically viable. However, spent craft yeast, which is higher in hop acid content than yeast from multinational breweries, could be useful as an antimicrobial feed supplement in ruminant livestock. To test the hypothesis that spent craft yeast will inhibit ammonia and methane production in the rumen, in vitro incubations were performed on caprine (n = 4) and bovine (n = 1) rumen fluid preparations using freeze-dried spent craft brewer’s yeast and baker’s yeast as a control. Caprine incubations yielded a significant drop in methane production for craft yeast at α = 0.1 (p = 0.059), but not for ammonia (p = 0.114), although a visual trend was observed. Bovine incubations showed a drop in both methane and ammonia consistent over 4 replicates. Effects on short chain fatty acid production was inconsistent with the literature for both caprine and bovine incubations, with reductions in both acetate and propionate production. Inhibition of pH drop was seen in the bovine incubations but not in caprine. This study supports the hypothesis that methane and ammonia production are inhibited by the use of spent craft brewer’s yeast, but repeat experiments are needed to prove statistical significance and assess impact on short chain fatty acid production.