Ron Olson, a 100-cow producer in northwest Wisconsin, was skeptical at first. But he decided to add yeast culture to his rations based on a recommendation from his nutritionist.
That was nearly 10 years ago. And, while it's difficult for Olson to say that yeast culture has boosted his milk production by "x" number of pounds, he is convinced it works.
"It's like an insurance policy to us now," he says. "Anytime there's a change in feed or amino acid profile, the yeast culture will be there to back us up."
Olson does whatever he can to boost his cows' dry matter intake, which includes feeding them several times a day. Keeping fresh feed in front of the cows has helped to boost his rolling herd average to more than 31,000 pounds.
Good managers, like Olson, are able to get a response from yeast culture. Generally speaking, that's what the research has shown over the years.
Studies not unanimous
Peter Robinson, extension specialist in dairy cattle nutrition and management at the University of California-Davis, has published two studies in the past year that would appear to contradict one another. Based on research Robinson performed at the Atlantic Dairy and Forage Institute in New Brunswick, Canada, the studies measured dry matter intake of yeast-supplemented cows.
In one study, published this past June in the Journal of Dairy Science, yeast culture didn't make a statistically-significant difference in the dry matter intake of cows fed the supplement 14 days precalving through 14 days postcalving.
Yet, a second study did show a positive response. Among cows that had calved more than once, dry matter intakes in the postcalving period were nearly 3 pounds per day higher than cows fed a conventional diet.
Results from the two studies could vary because of the way the experiments were set up, Robinson says. The second study – the one that showed a positive response – recorded data on more animals, and also followed the animals six weeks longer into lactation. "This allowed us to detect some differences that we weren't able to detect in the first study," he adds.
In the October 1994 issue of the Journal of Dairy Science, researchers at Penn State University didn't find an advantage to using yeast culture – relative to milk yield or dry matter intake – when cows were supplemented for 120 days postcalving. The cows were located at seven Pennsylvania farms.
The Penn State researchers went on to note, however, that other studies had found an advantage from yeast culture supplementation. They weren't able to explain the exact reason why, but did suggest that the variation in research results may be related to differences in yeast strains, the amounts fed, or various dietary factors at the farms studied.
"In the real world, there are so many variables that can affect a particular study," points out Charlie Stone, senior research scientist at Diamond V Mills, maker of a leading yeast culture product.
And, yeast culture supplementation presents a particular challenge for researchers. Not only are they dealing with management differences between farms or research sites, they are dealing with the complexities of the rumen – and, specifically, how the microbes in a cow's rumen use the nutrients in yeast culture.
"The microbial world is very dynamic, and response is highly confounded by environmental and dietary conditions," says Jane Leedle, gastrointestinal microbiologist and product development manager at Chr. Hansen Biosystems in Milwaukee, Wis., supplier of another yeast product.
And, some farms don't have the right nutritional management in place, while others do. "We figure 70 to 80 percent of the herds will respond to our product in a positive manner," Stone says.
Stimulates rumen bugs
Yeast makes sense. Think about it. We use yeast to produce foods for human consumption. Many products, like bread, would be nothing without it.
If given sufficient time, yeast will ferment the sugars in the bread dough to give off carbon dioxide, B-vitamins and other nutrients – many of which make the bread more palatable. You end up with bread that's highly nutritious and fun to eat.
Bottom-line: The yeast give off important nutrients in the fermentation process.
During fermentation, yeast cells release amino acids, organic acids, minerals, and enzymes into the environment, which stimulates the growth of certain rumen microbes.
According to an article by University of Georgia researchers this past September in the Journal of Dairy Science, yeast culture provides growth factors – organic acids, B-vitamins, amino acids – which stimulate the growth of rumen bugs that metabolize lactic acid and those that digest cellulose. Yeast culture also stimulates the growth of some proteolytic bacteria that digest protein.
And, we see an overall increase in the number of rumen bugs when yeast culture is provided.
In the November 1988 Journal of Dairy Science, researchers from the University of Kentucky noted higher concentrations of anaerobic and cellulolytic bacteria in the rumens of cows receiving yeast culture supplementation. (See the chart below.)
Karl Dawson, rumen microbiologist at the University of Kentucky, says subsequent studies have confirmed these results. In fact, most studies have turned up even more impressive differences in bacterial numbers between yeast-supplemented cows and control cows.
What are the practical implications of this? If you enhance microbial activity in the rumen, you enhance digestion rates, Dawson says. More digestion takes place in a shorter period of time.
Animals in first 40 to 60 days of lactation show the greatest response to yeast culture supplementation, says Mike Hutjens, dairy nutritionist at the University of Illinois. Yeast culture appears to stimulate the growth of fiber-digesting bacteria, he adds, which leads to greater digestive efficiency, volatile fatty acid production and dry matter intake.
For animals in early lactation whose energy needs are greater than their normal dietary intake, that can make a big difference.
A majority of the research trials involving yeast culture have shown positive results.
This past summer, at the annual meeting of the American Dairy Science Association, researchers from the University of Illinois released a study showing a 4.7-pound-per-day increase in dry matter intake for Jersey cows fed a yeast culture supplement during the last seven days prepartum compared to cows fed a control diet without yeast culture. And, yeast-supplemented intakes were 3.9 pounds per day higher during the first 42 days of lactation.
That particular study monitored dry matter intakes. What about milk yields? The results from eight research studies are summarized in the chart, "Most studies show a boost from yeast supplementation," located at the top of this page.
Look at the results. On an average basis, the studies show roughly a 3- to 4-pound-per-day advantage to using yeast culture during early lactation.
With that kind of response, the product pays for itself. Diamond V's Charlie Stone says it will usually cost four to five cents per cow per day to feed his company's product, depending on the dealerships involved and geographic location. But assuming that cost, and a 3-pound-per-day production response, and milk priced at $12 per hundredweight, the return on investment is somewhere in the neighborhood of 7:1 to 9:1.
Diamond V takes an even more conservative approach by saying there is a 3:1 to 4:1 return on investment on the product.
Regardless, if you are looking to increase return, you may want to investigate yeast cultures.
More yeast, more bacteria
Total anaerobic bacteria
Yeast-supplemented cows: 12.3 billion
Non-supplemented cows (control): 7.8 billion
Total cellulolytic bacteria
Yeast-supplemented cows: 120 million
Non-supplemented cows (control): 66.1 million
Source:Journal of Dairy Science, November 1988.
Most studies show a boost from yeast supplementation
|Study||Yeast-supplemented cows||Non-supplemented cows||Difference (lbs/day)|
|Penn State University, 1994 (1)||70||70||+0.0
|University of Wisconsin and Diamond V Mills, 1995 (2)||82.6||80.7||+1.9|
|Atlantic Dairy and Forage Institute, 1996 (3)||89.0||85.1||+3.9|
|Atlantic Dairy and Forage Institute, 1997 (4)||76.2||75||+1.2|
|University of Delaware, et al, 1997 (5)||86.5||80.1||+6.4|
|University of Idaho, et al, 1997 (6)||92||86.9||+5.1|
|University of Illinois, 1997 (7)||50.9||47||+3.9|
|Rutgers University, 1997 (8)||89.5||82.9||+6.6|