STATE COLLEGE, Pa. – When mushrooms are harvested for human consumption, the edible head or cap is separated from the fibrous stump. The stump waste is then either sent to a facility to be composted or disposed of. On average, 29 percent of the total mushroom weight is stump waste.

Researchers from Pennsylvania State University (PSU) are interested in taking that stump waste and adding it as a supplement to chicken feed.

“The poultry industry is well known for converting waste streams into nutrient streams, and this just seemed to make a lot of sense,” John Boney, assistant professor of poultry science at PSU, said.

There are plenty of examples of human food waste being put to good use as animal feed. When cookies, cakes, and crackers don’t make the aesthetic cut for human consumption, the waste is often ground into a bakery byproduct that becomes an animal food source. Mushroom waste is of interest in Pennsylvania because the state produces 64 percent of all button mushrooms in the U.S. Approximately 93,264 metric tons of button mushroom stumps are composted yearly as a waste product.

Boney said the key to feeding the growing population will be to become as sustainable and as efficient as possible. “So if mushroom producers are able to grow their mushrooms, sell the edible cap portion, and then sell their stumps to us (to use in chicken feed), we’re able to improve efficiency. We’ve eliminated a waste stream and enhanced the efficiencies of two different segments of food production.”

Boney and his team studied 480 broiler chickens purchased from a commercial hatchery to understand the impact of including mushroom stump waste in chicken feed. The birds were placed in one of six dietary treatment groups, with some receiving no fungi supplementation and others receiving 1-5 percent mushroom stump waste in their feed. The researchers specifically studied how well the birds digested 17 amino acids associated with the stump waste and how this affected their growth and health.

“We’ve found that you can feed up to 3 percent of this mushroom stump without any detriment to performance. So, what that means is that you can take your typical diet that you’re feeding broiler chickens, you can formulate this mushroom stump ingredient in at 3 percent of the diet, essentially requiring less of other things like corn and soybean meal, and maintain the same level of performance that you normally achieve,” Boney said.

Interestingly, the team also found that beginning at the 1 percent inclusion rate, broiler chickens consuming the mushroom stump waste-supplemented feed demonstrated performance enhancement in several categories, including body weight gain, final body weight, and how well the chickens converted feed into weight gain.

“There’s a lot of bioactive compounds in mushrooms that humans get when they consume the edible cap portion, and we assume that some of those components are still active even in the stump,” he said, adding that further studies would be required to prove this theory. “There may be a way to refine that inclusion rate so that instead of just maintaining performance, you can actually get a performance or an efficiency improvement and continue to produce poultry in a really cost-effective manner.”

While Boney and his team can’t put a price on mushroom stump waste as a feed supplement, he said that whenever a waste product is converted into something usable, it is cheaper than other feedstocks. Feed costs for producing broiler chickens account for 60-70 percent of the total production cost, so finding cheaper alternatives will benefit farmers.

However, the work has not been commercialized, nor has the FDA approved mushroom stump waste as a poultry feed supplement. There is still a lot of work ahead before it hits the market, with Boney adding that researchers at PSU are interested in taking steps toward creating a usable and sellable product.

“What will need to be done next is to find out how the stump product received from the commercial mushroom farms can be efficiently converted from a waste product into a feed ingredient,” he said. The team will need to figure out how to remove moisture from the waste and ensure that it’s a shelf-stable product that can be commercialized.

Although Pennsylvania produces the most button mushrooms and has the most stump waste, Boney said the work could easily be translated to other locations producing mushrooms if mushroom growers could develop or use existing technologies to create the usable feed ingredient.