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Virginia Cooperative Extension - Knowledge for the CommonWealth

Ration modifications for hot weather

Dairy Pipeline: June 2002

Charles C. Stallings
Extension Dairy Scientist, Nutrition
(540) 231-4758

When the weather gets hot the best rations for dairy cows are the ones that are most digestible. Feeding more digestible feeds such as grains and/or using forages that are less mature and lower in fiber and lignin can increase digestibility. Digestible rations will have a faster rate of passage out of the gastrointestinal system and result in greater feed intakes than with rations of lesser digestibility. The exception can be situations where rumen acidosis occurs due to overfeeding grains or starchy feeds. The roughage requirement must be met first. Sodium bicarbonate can be added to buffer higher levels of grain. Add one-third to one-half pound per cow per day. Some fat can be added to rations during hot weather to increase energy density. Do not exceed 6% fat in the dry matter, however. Avoid overfeeding protein because it takes energy to excrete excess nitrogen. This is energy that can be used for milk production. Rations greater than 18% protein are not usually advisable and sometimes less than this is adequate depending on production level. Also avoid rations that have high levels of rumen protein degradability (greater than 65% degradable) for the same reason. Research has demonstrated that hot weather increases the need for certain minerals. This is due to increased sweating and urination resulting in more minerals being excreted. Potassium should be at least 1.5% of the ration dry matter, sodium .45%, and magnesium .35%. Other considerations for maintaining dry matter intake are feeding more frequently to keep feed fresh, feed during cooler times of the day, providing adequate feed bunk space so cows can eat without crowding, providing plenty of cool water, and maintaining air flow with fans. Keeping cows eating is the key.

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