Effects of hops treatment on nitrogen retention, volatile fatty acid accumulations, and select microbial populations of composting poultry litter intended for use as a ruminant feedstuff

Authors: CASTILLO-CASTILLO, YAMICELA - Universidad Autonoma De Chihuahua; ARZOLA-ALVAREZ, CLAUDIO - Universidad Autonoma De Chihuahua; FONSECA, MOZART - University Of Nevada; SALINAS-CHAVIRA, JAIME - University Of Tamaulipas; ONTIVEROS-MAGADAN, MARINA - Universidad Autonoma De Ciudad Juarez; HUME, MICHAEL - Retired ARS Employee; Anderson, Robin; Flythe, Michael; Byrd Ii, James - Allen; RUIZ-BARRERA, OSCAR - Universidad Autonoma De Chihuahua

Submitted to: Microorganisms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/23/2023
Publication Date: 3/25/2023
Citation: Castillo-Castillo, Y., Arzola-Alvarez, C., Fonseca, M., Salinas-Chavira, J., Ontiveros-Magadan, M., Hume, M.E., Anderson, R.C., Flythe, M.D., Byrd II, J.A., Ruiz-Barrera, O. 2023. Effects of hops treatment on nitrogen retention, volatile fatty acid accumulations, and select microbial populations of composting poultry litter intended for use as a ruminant feedstuff. Microorganisms. 11(4). Article 839. https://doi.org/10.3390/microorganisms11040839.
DOI: https://doi.org/10.3390/microorganisms11040839

Interpretive Summary: Poultry litter is a byproduct of the poultry industry that can be challenging to dispose of. If appropriately treated to kill pathogens, the litter can be a potentially valuable fertilizer or crude protein feedstuff for ruminants. Composting economically and effectively kills pathogenic microbes but risks loss of valuable nitrogen during microbial degradation. Hops, which are plant materials commonly used to manipulate microbes during beer production, have been reported to exert antimicrobial activity against a variety of pathogenic and nitrogen degrading microbes. Consequently, we hypothesized that adding extracts of these plant products to composting poultry litter may aid in the antimicrobial effectiveness of the composting process while at the same time preventing the loss of valuable nitrogen. In three experiments, we tested the effects of two different sources of hops, called Chinook or Galena, on the antimicrobial activity and nitrogen retaining ability during composting of poultry litter. Results from our experiments did not support our hypothesis as low- and high-dose hops treatments had no benefits on the antimicrobial effects of composting, which by itself was effective in decreasing populations of pathogenic microbes. Similarly, the hops treatments had no beneficial effect on the nitrogen retaining ability of the composting poultry litter. Serendipitously, however, we observed that the hops treatments dramatically decreased the accumulation of a volatile spoilage product, called butyric acid, that can adversely affect the attractiveness of the composted material for use as a feed or fertilizer. Moreover, these results indicate that hops treatments such as these may also be useful in preventing spoilage of other fermented feedstuffs such as silage often used by dairymen. Ultimately, these results may help U.S. farmers and livestock producers better manage and recycle bioproducts of animal agriculture, thereby reducing costs while conserving what otherwise would be wasted resources.

Technical Abstract: Poultry litter, if appropriately treated to kill pathogens and antimicrobial resistant microbes, can be a potentially valuable fertilizer or crude protein feedstuff for ruminants. Composting effectively kills pathogens and antimicrobial resistant microbes but risks losses of ammonia during uric acid degradation. In our first experiment, we tested the effects of 0.26% Galena or 0.09% Chinook hops treatments (wt/wt) on antimicrobial activity and nitrogen retention during 9 days of simulated composting of wood chip poultry litter. Results revealed no beneficial effects (P > 0.05) of the hops treatments on the antimicrobial effects of composting which in the untreated control was effective in decreasing populations of Salmonella Typhimurium, Escherichia coli, and total culturable aerobes. Effects of hops treatment on accumulations of ammonia and urea were observed during the composting period but not on uric acid accumulations. In the case of ammonia, concentrations on day 9 of composting were 14% lower (P < 0.05) in Chinook-treated composts than untreated composts (13.4 ± 1.06 umol/g compost dry matter) whereas in the case of urea, average concentrations over the course of the 9-day composting period were 55% lower (P < 0.05) in Galena-treated litter than in control litter (6.2 ± 1.72 umol/g compost dry matter). Uric acid accumulations were not affected by hops treatment during the compost period but were higher (P < 0.05) after 3 days of composting than when sampled after 0, 6, or 9 days composting. Follow up experiments were conducted to test the potential effects of Chinook or Galena tannin extracts, each administered at 0.7% (wt/wt) to simulated composts (14 days) of wood chip poultry litter alone or mixed 3:1 with ground Bluestem hay (Andropogon gerardii). Results revealed that even at these higher hops dosages, little if any beneficial antimicrobial effects (P > 0.05) of the hop extract treatments were observed during composting on populations of total coliforms, enterococci, lactic acid bacteria, staphylococci, or yeast and molds, with composting by itself achieving (P < 0.05) reductions in microbial counts exceeding 2.5 log10 colony forming units/g compost dry matter. Likewise, little if any beneficial effect of the hops treatments were observed on accumulations of ammonia, urea or uric acid when compared to untreated controls. Accumulations of volatile fatty acids in the composted litter were affected by the 0.7% hops treatments, however, with accumulations of butyrate in the hops-treated compost being dramatically lower than those observed in untreated controls after the 14-day compost period. Overall, the results indicate that under the conditions of the current studies the hops treatments had little if any added effect on pathogen control or nitrogen retention within the composted poultry litter but did lessen accumulations of butyrate which may lessen adverse effects of this fatty acid on palatability of litter fed to ruminants.