Heat stress in dairy herds can be a serious problem in Japan and Illinois. Milk production can decline 30 percent or more, components shift, reproduction declines and metabolic disorders can be life threatening.

Nutrient challenge with heat stress

A number of factors occur when cows are under heat stress which can impact the feeding program.

1. Feed intake declines due to the heat of digestion adding to the heat load of the cow (Table 1).
2. Blood flow is reduced to the digestive tract as cows attempt to dissipate heat.
3. Digestibility increases slightly due to greater retention time in the digestive tract.
4. Maintenance requirements increase to regulate heat by over 30 percent to cows in thermal neutrality (Table 1).
5. Cows will eat during cooler times of the day resulting in variable intake patterns.
6. Farmers will decrease forage intake in an attempt to increase energy intake and reduce heat of digestion (also called heat increment).
7. Wet feeds can heat up in feed bunks due to secondary fermentation, lack of shade, and low quality silage.
8. Rumen acidosis is a greater risk because of variable intake, slugging of grain, and feed selection.
9. Adding fat as oilseeds (such as soybeans or cottonseeds) can increase

These factors indicated energy intake, rumen digestion, and rumen acidosis must be managed and buffers can be one management solution.

Role of buffers

Mineral interactions

Higher levels of sodium (from .18 to 0.5 percent) in the total ration dry matter be beneficial (Table 3). Sodium was excreted in urine while potassium losses occurred due to sweating. Florida workers suggest a ratio of 3 part potassium to 1 part sodium (1.2 to 1.5 percent potassium and .4 to .5 percent sodium. Magnesium should also be increased from .25 to .35 percent of the ration dry matter. Higher cationic rations (from =180 to +350 meq per kg) increased dry matter intake (equation: sodium + potassium - chlorine calculated on a meq basis).

Strategies with buffers

1. Add .75% of the total ration dry matter as sodium bicarbonate or sodium sesquicarbonate ( 25 kg D.M. X .0075 = 187 grams/cow/day)
2. Supplement a buffer under the following conditions, especially with heat stress occurring:
   1. Total ration ADF below 19%
      
   2. Total ration NDF below 28%
      
   3. Forage NDF below 21%
      
   4. Feeding more than 3 kg of grain per meal
      
   5. Feeding more than 2% of cow's body weight as forage
3. When a buffer pack is added, monitor dry matter intake (increase over 1 kg is desirable).