In last month's Nutritionist e-Network, we summarized a research experiment from Israel that showed the effectiveness of live yeast supplementation in warm weather. The experiment was originally published in the January 2009 Journal of Dairy Science.

We did not know at that time that another study was about to appear in the March 2009 edition of the Journal of Dairy Science. That study, conducted by researchers at the University of Arizona, found no benefit from a yeast culture under climate-controlled heat-stress conditions. The Arizona researchers used a "novel yeast culture formulation" or proprietary blend of two active yeast strains, cobalt chloride and a vitamin mix containing biotin and niacin. The Israeli researchers used the live yeast Saccharomyces cerevisiae. So, there were some key differences between the studies in terms of the type of yeast used. And, cows in the Arizona study were subjected to severe heat stress, with body temperature readings approaching 105 degrees F. The Israeli researchers did not report ambient temperature or body temperature readings; they simply referred to the use of live yeast supplementation during the hot season in Israel. Obviously, the jury is still out when it comes to yeast culture and heat stress.