In a February 2007 article titled, "Why heat stress steals milk," the editors of Dairy Herd Management told a producer audience, "Consider adding yeast culture to the diet (under heat-stress conditions). A diet containing supplemental yeast culture may help the rumen utilize nutrients more efficiently." That recommendation has now been confirmed by researchers at the Volcani Center in Israel. They found that cows supplemented with live yeast (Saccharomyces cerevisiae) had higher dry-matter intake (54.3 pounds per day vs. 53 pounds), higher average milk yield (83.2 pounds vs. 79.9 pounds) and 3.7 percent greater feed efficiency than control cows.

The experiment began in mid-July and continued until mid-October, which is the typical hot season in Israel. Their experiment is described in the January 2009 edition of the Journal of Dairy ScienceThe JDS article described the properties of yeast culture in a general sense. In a subsequent e-mail exchange with Nutritionist e-Network editors, lead researcher Uzi Moallem of the Volcani Center in Israel described why live yeast may be particularly important in hot weather. He said live yeast appears more beneficial under stress conditions, such as early lactation or hot weather, and less effective when rumen conditions are normal. Under stress conditions, it might be that live yeast helps stabilize the rumen environment by increasing the pH and creating optimal conditions for microflora development.

"This might increase the feed intake, as was demonstrated in our study, and enhance the production," he said.