UC Davis

California produces 2.55 billion pounds of almond kernels annually, and along with that 4.03 billion pounds of byproduct almond hulls are generated. Almond hulls have high sugar contents and are mainly used as livestock bedding and feed at present. The almond industry is seeking ways to reduce the environmental impact of conventional almond production by reducing dust generation and achieving zero waste. Off-ground harvesting is an emerging harvesting strategy that generates significantly less dust; however, off-ground harvesting produces a stream of wet hulls that can easily spoil if they are not processed properly. Wet almond hulls are an ideal feedstock for fermentation into high quality, probiotic-rich animal feed which can help the almond industry meet its zero-waste goal and increase revenue for almond farmers. Fermented animal feed is an alternative to the use of growth-promoting antibiotics in livestock and has already been recognized as an effective tool to improve gastrointestinal health and improve productivity in swine and poultry. It is possible that similar benefits can be observed in cattle fed fermented feed. Additionally, studies have shown that probiotic supplementation and alternative feeding strategies can reduce ruminant methane generation, the largest source of anthropogenic methane emissions in the US. The goal of this study is to assess the potential of using almond hulls as a feedstock for the production of a fermented cattle feed which can potentially reduce the environmental impact of the almond industry while concurrently increasing the value of almond hulls, improving cattle digestion, and reducing enteric methane emissions. In this study, California almond hulls of Nonpareil, Monterey, Independence, and Fritz varieties from a hulling facility were characterized for their chemical composition. The hulls had high sugar contents ranging from 31.8% to 42.2% by weight on a dry-basis (db) and phenolic compound content ranging from 3.4% to 7.6%, db. On- and off-ground harvested hulls of Independence, Monterey, and Fritz varieties were also characterized and compared. Off-ground harvested hulls had an average moisture content 3.5 times higher than on-ground harvested hulls of the same variety. Hulls were low in protein and fat at an average of 5.7% and 3.7% db, respectively and an average of 24.1% acid detergent fiber and 33.3% neutral detergent fiber. The hulls were characterized for the quantity of contaminants vs. hulls and on average, hull samples contained 88.9% hulls and 10.1% contaminants. Sieving and terminal velocity analysis were conducted to investigate methods for separating hulls from contaminants. The results showed that sieving separation was an effective method for separating hulls from contaminants. Solid-state, inoculated fermentation trials were conducted using Saccharomyces cerevisiae and Lactobacillus plantarum as inoculums. The effect of inoculum type, fermentation duration, inoculum amount, hull variety, particle size, and fermentation temperature were investigated through several fermentation experiments. It was found that fermentations using S. cerevisiae produced higher amounts of ethanol and acetic acid and caused an increase in pH, and fermentations using L. plantarum produced higher amounts of lactic acid and caused a drop in pH. Hull variety had a large impact on the characteristics of the fermented hulls under the conditions tested. 14-day fermentation durations produced similar results as 30-day fermentation durations in the conditions studied. Additionally, in-vitro digestion results indicated that almond hulls fermented with S. cerevisiae for 14 days reduced enteric CH4 production by 96% over 72 hours digestion at a 20% inclusion rate in a cattle diet. The nutritional composition of almond hulls, especially their high sugar content, makes them an ideal feedstock for the creation of fermented cattle feed. Almond hulls fermented with S. cerevisiae and L. Plantarum produce desirable characteristics for fermented feed including a pH below 4.5, high concentrations of lactic acid, and low concentrations of acetic acid. In-vitro digestion tests suggest that fermented feed is potentially an effective strategy to reduce enteric CH4 production.