In July, central Illinois had 16 days over 90 degrees (one of the hottest months in history). Midwest dairy managers knew all about the challenge as dry matter intakes dropped 5 to 10 pounds followed by milk declines of 5 to 15 pounds.Perhaps August will be a cooler month, but the following points may be useful.

1. A northern Illinois dairy producer asked what he could due to recover lost milk. Great question with few research-proven answers. Building a more nutrient dense ration package is possibility. One approach is to rebalance your ration reducing dry matter intake by five pounds. Fiber and starch restrictions will become factors that can stop your computer. Adding fat and oil can provide extra energy if dry matter intake continues to lag. A southern Illinois producer added wet brewers grain stimulating his cows to eat more. The wet by-product feed can improve palatability (he had his stored in a plastic bag), increase ration moisture, and offered a change in his ration. Feeding rations at different times and frequencies may get cows started. Watch cows less than 120 days in milk to see if they can bounce back more compared to longer lactation (stale) cows. If these mid lactation non-responding cows are not on BST, you may be able to increase milk production 10 to 15 pounds with this technology.
2. Watch your corn crop closely as the hot weather can push corn maturity more rapidly. Be ready to chop corn silage at 30 (bunkers and plastic bags) to 35 percent (conventional silos) dry matter. If corn is drought stress due to spotty rain or light soil, again monitor plant moisture and be ready to harvest when it is ready. High moisture corn can also be ready to harvest earlier than normal. High moisture corn below 25 percent moisture does not ferment as complete and can be digested (fermented in the rumen) like dry corn. Evaluate corn grain particle size.
3. At a Pennsylvania feed dealers meeting, the effects of panting and heat stress were discussed. When cows were breathing heavily and rapidly (over 80 breaths per minute), little if any rumination can occur. Cows may also lose puddles of saliva and foam while panting. Finally, as cows rapidly respire, they blow off extra carbon dioxide reducing blood buffering capacity and leading to metabolic acidosis (no clear conclusion was reached if this could also contribute to rumen acidosis).
4. A recent Canadian study demonstrated the impact of DCAD (dietary cation-anion difference) in early lactation cows. Seven dietary treatments with ten cows per treatment were fed for the first 10 weeks of lactation. Experimental diets had supplemental sodium bicarbonate and/or potassium bicarbonate to increase DCAD. Table 1 lists the treatments and results. Several interesting conclusions can be drawn from the study.

• Increasing DCAD to +180 meq/pound may improve dry matter intake.
• If dry matter increases, milk production can be increased.
• Blood buffering can be an important consideration.
• Higher potassium and sodium levels are needed under heat stress conditions.
• Test feeds and balance for sodium (0.4 to 0.5%), potassium (1.5 to 1.8%), magnesium (0.3 to 0.35 percent), and chlorine (0.3 to .35%).
• Check potassium to magnesium ratio (4:1).
• Check potassium to sodium ration (3:1).

Additional research is needed before to high DCAD levels are recommended (an optimal level may be +115, +175, +236, or higher meq/pound value especially at higher temperatures and humidity).

Table 1. Impact of higher DCAD levels using added levels of sodium bicarbonate (Na bicarb) and/or potassium bicarbonate (K bicarb) in early lactation (Source: Block, Canada).

* Values significantly different from control value (P < 05)
** Values significantly different from control (P < 01)