Can yeast mitigate heat stress in cows? It depends on the type of yeast being used.

In our Feb. 20, 2009, Nutritionist e-Network newsletter, we told you about research from Israel showing that cows supplemented with the live yeast Saccharomyces cerevisiae in hot weather had higher dry-matter intake, higher average milk yield and greater feed efficiency than control cows.

Lead researcher Uzi Moallem told the Nutritionist e-Network editors in an e-mail that live yeast may be particularly important in hot weather. But, the following month, we reported on another experiment — this time from the University of Arizona — where yeast culture supplementation did not work in warm weather.

The difference? Different types of yeast were used in the two studies. Now, the Israeli research appears to be collaborated by researchers at the University of Florida. Researchers found that cows receiving the same type of live yeast — Saccharomyces cerevisiae (although a different strain) — as cows in the Israeli study had greater feed efficiency and true milk protein yield and reduced risk of subacute rumen acidosis under heat-stress conditions.