University of Minnesota specialists also say to make sure high moisture feed ingredients (distillers and corn gluten) are fed before they experience secondary fermentation (heating), and consider using a bunk stabilizer such as propionic acid. These commercially available products reduce growth of yeast and molds in silage when added during the ensiling process.
Additional management techniques include minimizing TMR sorting by increasing feed push up and evaluating particle size, managing bunker faces to minimize exposure to oxygen by removing only the amount of feed from the bunker needed to feed cows within the hour, and avoiding mister spray onto feed. The specialists say excessive wetting of the TMR can reduce palatability and accelerate bacterial growth in the bunk reducing feed quality.
Finally, keep a clean bunk. Remove all feed refusals daily before any new TMR is fed. Avoid TMR dry matter content less than 50%. Also plan on lower dry matter intake during heat stress and work with your nutritionist to adjust diets accordingly. An example is to increase the nutrient density of the diet to reflect actual dry matter intake, which is typically reduced during heat stress.
Feed ingredient adjustments:
Litherland and Sawall recommend increasing the energy density of the diet and reducing the heat of fermentation by substituting carbohydrates with rumen inert fat. Supplemental saturated fatty acids at 1.5 or 3.0% of diet dry matter have been shown to increase milk yield, milk fat content and yield, and reduce peak rectal temperatures in heat stressed cows.
They also say to increase delivery of key minerals, including phosphorous, potassium and sodium. Supplementation to increase dietary potassium from 1.0% to 1.5% in heat stressed cows in Arizona increased milk production. Research also indicated that increasing the dietary cation-anion difference for lactating cows increased milk yield when sodium (sodium bicarbonate) and potassium (potassium carbonate) were added to the diet. Avoid excessive concentrations of dietary sulfate and chloride in lactating cow diets especially during heat stress.
Supplement TMR with yeast culture. Research has shown feeding yeast culture improved daily milk yield by 2.6 pounds per cow during heat stressed conditions in California.