Adding fat to the diet: Adding fat to the diet is expected to decrease heat produced during the digestion of feeds while increasing the amount of energy available. Studies where fats have been fed to heat-stressed cows have shown inconsistent responses in improving milk production; some have improved milk production, and others have shown no response.
Adding yeast cultures to diets: Yeast culture has been shown to improve fiber digestion and stabilize the rumen environment. In heat-stressed dairy cows supplemented with yeast, lower rectal temperatures and respiration rates were observed in several but not all studies. Several studies, but not all, have shown an increase in milk production of heat-stressed cows supplemented with yeast. In 1994, Huber and other summarized 14 lactation comparisons with 823 heat-stressed cows where yeast was or was not added to the diet. Overall ,these comparisons showed a 2.2 pound/day increase in milk production with yeast supplementation with six comparisons showing significantly higher milk production with supplementation , three slightly higher, and the remaining five comparisons with no or slightly lower milk production. Two recent studies have shown no improvements in milk production with yeast supplementation, but one indicated improved feed efficiency. Early-lactation cows fed a higher proportion of concentrate may respond more favorably to yeast supplementation than mid- to late-lactation cows.