Ray and Rhett Smith of Smith Ranch in Taloga, OK, start or precondition 5,000 head of calves and cutting bulls a year. In the early 1990s, a feed additive -- yeast culture -- caught their attention for two reasons:

* Its ability to enhance ration palatability and dry matter intake.

* Its ability to nurture existing populations of rumen microbes for increased digestibility of feedstuffs.

As a test, the Smiths split a group of starter calves into two pens, both on the same management program but with one pen receiving yeast culture.

'The health of the calves on yeast culture was a lot better,' says son Rhett. 'There were fewer sick calves. If they did get sick, it seemed they recovered faster. That pen also gained more.'

Since then, yeast culture has been part of their program. Starter calves receive good prairie hay and water on arrival. The second day, yeast culture is introduced for the duration of their 28- to 45-day stay. They use a similar program for cutting bulls, but include a supplement with slightly lower protein.

Yeast Or Yeast Culture? Many cattlemen confuse yeast culture with high cell count yeast. They do share a common ingredient -- yeast, but the yeast culture is uniquely fermented, says Marlan Francis, DVM, director of technical services for Diamond V Mills.

Yeast culture consists of fermented yeast and the media on which it's grown. This media is rich in nutritional metabolites produced by the yeast cells during the fermentation process.

But, many high cell count yeast products are made by mixing active dry yeast with one or more carriers. These carriers might include distillers' dried solubles, ground corn, hominy or ground rice hulls. No fermentation occurs.

'It's like spiking grape juice with alcohol and expecting a fine vintage wine,' Francis notes.

The role of yeast culture in rations is receiving increasing attention. Major suppliers of cattle feeds and concentrates now incorporate it into starter feeds and mineral mixes.

Consolidated Nutrition (CN) of Omaha, NE, for instance, added yeast culture to its free-choice minerals and weaning/receiving feeds in 1997. Why? Its positive effect on rumen microflora, ability to increase dry matter intake -- important in stress situations -- and its ability to provide a consistent response, says Bill Schmutz, CN cattle nutritionist.

But, the turning point was its ability to survive the pelleting process, he adds. This process kills most live yeast cells but doesn't affect yeast culture. The nutritional metabolites exist with the fermentation media, not the yeast.

Farmland Feeds' starter feeds (and mineral mixes) have contained yeast culture for five years. After doing research with yeast culture vs. yeast, they found yeast culture produced more consistent results with increased intake in fresh calves.

Farmland's beef nutritionist Dan Colling says Montana State University research indicates mineral absorption may increase with yeast culture in the mix. 'If so, we may want to consider increasing the amount of yeast culture in our mineral mixes,' he says.

Consultant Comments Yeast culture has also caught the attention of beef nutrition consultants such as Jim Simpson, Simpson Nutrition Services, Canyon, TX. Simpson works with starter calves and feedlot cattle.

He says starter calf trials with yeast cultures have consistently shown improved intake, efficiency and gain, as well as reductions in sickness and death. The responses are partly due to improved nutrient utilization in the rumen, he says.

Simpson says intake stimulation in stressed calves plays an important role in the overall success of starting programs. By encouraging intake of balanced rations, nutrient deficiencies are more rapidly corrected, resulting in improved feeding period performance.

In feedlots, most yeast culture usage is in receiving and convalescent programs for stressed calves. It's also used in mineral formulations to encourage intake.

'Yards I work with routinely top dress yeast culture to timid, stalled or new cattle slow getting on feed or not maintaining adequate intake,' he says.

One field trial examining yeast culture use in hospital programs found intake of hospital feed increased, while repulls fell, Simpson says. The trials were on long-haul lightweight calves. Initial pull rates of 50-60% were common with 10-24% repull rates normal.

When yeast culture was top-dressed on the hospital feed, intake improved an average of 0.5% of body weight while in the hospital. Repulls were halved in each of the three reporting periods spanning two years, he says.

Some consultants, however, remain skeptical and continue to ask for more research results from universities or other objective third parties. They discount on-farm or feedlot trials as well as producer testimonials because of the variables that can affect results.

One, Richard Zinn of the University of California-Davis, says that 'while yeast culture products may have merit, they're lacking in the number and quality of research results found for other products commonly used in feedlots.'