Survey of yeast populations in fermented feed across the United States

Yeasts are single-celled, facultative anaerobic eukaryotes that are prevalent in various fermented feeds. Yeasts can negatively affect silage quality by metabolizing available nutrients within the feed which leads to dry matter loss and decreased nutritive value, and by producing ethanol which can lead to off flavors in milk when consumed. Yeasts also oxidize lactic acid, which increases silage pH and promotes the growth of organisms such as mycotoxin-producing molds. Although wild yeasts can have a negative effect on feed quality, the prevalence and identities of these organisms in different crop types are not well studied. The objective of this survey was to examine yeast populations in fermented feed from various sites across the United States. From April 2019 to July 2022, 438 samples of 3 different crops (alfalfa haylage; n = 132), corn silage (CS; n = 272) and high moisture corn (HMC; n = 34) were collected from more than 130 farms across 16 states. Yeasts from these samples were enumerated on potato dextrose agar with 0.15% tartaric acid. Isolates were then harvested and DNA was extracted. Species were identified by sequencing the fungal ITS region. From the feed samples that were analyzed, yeasts were detected more often in HMC (76.5%) than alfalfa haylage (50.8%; P < 0.05). Yeasts were detected at higher levels in HMC compared with both alfalfa haylage and CS (P < 0.0001). The CS had the highest species diversity (14 species), with a Shannon-Weiner index value of 2.2, whereas HMC had the lowest diversity (4 species), with a Shannon-Weiner index value of 0.99. Pichia kudriavzevii, Pichia fermentans, and Saccharomyces cerevisiae were common species found across all 3 feed types. P. fermentans was the most prevalent species in both CS and alfalfa haylage, whereas Wickerhamomyces anomalus was the most prevalent species found in HMC. Overall, the data gathered provides a better understanding of yeast levels and populations found in various fermented feeds across the United States. This knowledge can be used in future research to identify novel methods to inhibit yeast growth within fermented feed.

Key Words: yeast, silage, fermentation.