Yeast cultures are nutrition products exceedingly difficult to assess. First, most are proprietary, so research with one product can't be extrapolated to another.
Yeast cultures also have special legal status - considered neither a drug nor a nutrient. With one exception (high selenium yeast), yeast products aren't subject to FDA or state regulation.
Such nutrition products as vitamins and minerals typically have broad bases of research. In clearing drugs, FDA requires that efficacy be proven. Thus, a broad base of research is available for virtually all drugs on the market.
But the research available for most yeast products is limited. And, what's available has primarily been sponsored by the parent company.
These products, however, shouldn't be confused with various "spent" yeast products on the market. Spent yeasts are by-products of food and beverage manufacturing. Typically, these yeasts are autoclaved (cooked at very high temperatures) to kill the yeast. They become a true nutrition product - consisting of high-quality protein and a rich source of B vitamins. And they're sold on that basis.
Brewer's yeast is the most common and is an excellent feed for cattle. Due to the high biological value of the protein, however, the monogastric animal feed industry usually bids it out of our reach.
Enhanced Fiber Digestion Commercial yeast products are claimed to have value above and beyond the protein or B vitamins we find upon analysis. Many claims are made but one does seem to be confirmed by research - some of these products seem to enhance fiber digestion in the presence of an acid pH.
That is, as we begin adding grain to a forage-based ration, the pH drops (acidity of the rumen increases). As acidity increases, cellulolytic bacteria and protozoa begin to die off, and the digestion of fiber declines. That's why in the feedlot we typically either feed a high-forage "growing" ration or a high-grain "finishing" ration. Anything between is inefficient.
With dairy cows, however, the nutritionist is forced to use relatively high levels of grain in forage-based rations. The grain is needed to maximize milk production, but forage is needed to maintain rumen health and maintain acceptable butterfat levels.
Yeast In Feedlots Obviously, these yeast products have the greatest application in dairy, and that's where most yeast product research has focused. But, recently I ran into a situation that seemed to indicate some sort of yeast or other biological product might be of value.
At a by-product feedlot in which bakery products are the primary ration ingredients, a supply of fermented bagels became available. Upon adding the bagels to the ration, the feedlot owner reported scouring.
Investigating, we found that maltose (a special type of sugar) is sometimes used in bagel recipes. Unfortunately, almost nothing is known of maltose in ruminant digestion. My guess was that rumen bacteria either could not use maltose or the fermentation products present in the bagels. As a result, we were getting a secondary fermentation in the large intestine (cause of the scouring).
I contacted the major suppliers of yeast culture products. One of them, Diamond V Yeast, agreed to donate some product. My hope was to find some sort of organism that could colonize the large intestine and utilize the fermentation products that were apparently causing the problem.
As stated in the beginning, commercial yeast products can't be compared with one another. Diamond V is no exception. According to the Diamond V people, their product is not a live yeast, but a collection of fermentation products. This threw out my idea of colonizing the large intestine. But we tried it and it worked.
It Worked, But How? Fed at 2 oz./hd./day, scouring in the treatment group subsided after a few days. Neither I nor the Diamond V technical people can explain the mode of action, but the feedlot owner definitely noticed a difference.
One of the headaches associated with by-product feedlots is the constant ration adjustment due to supply problems with ingredients. This was no exception. Just three weeks into the "trial," the supply of fermented bagels dried up. We replaced the bagels with sweet rolls and donuts (which weren't fermented), and scouring in the untreated group stopped.
One problem in doing feedlot research is that feedlot owners usually aren't interested in the science and data. They just want their problems solved. Such was the case here.
When we first ran out of bagels, it was thought more would be coming, and I couldn't convince the feedlot owner to catch a check weight (wanted to use the final closeout). But, we didn't get any more. As a result, we have no data. But, the exercise was an eye opener. Many biological products (bacteria and yeasts) are sold under the claim they can colonize the large intestine. Unfortunately, there have been many failures.
But in this case, we did have a response. Unfortunately, I don't know what the response was or how economically significant it would have been.