Current Progressive Dairy digital edition

1008 PD: Help cows beat the heat with good management

Bill Zimmer Published on 30 June 2008

Heat stress can cost dairy producers big bucks, especially during the summer months.

Research has shown that milk production losses alone range from $1.45 to $2.90 per cow per day.



In addition, reproductive losses resulting from heat stress may include missed heats, low conception rates, low birth weights, difficult births and metabolic problems after calving. With total losses ranging from $3 to $4 per cow daily, it is easy for heat stress to cost a producer $10,000 or more per month for every 100 cows.

The ideal ambient temperature for a dairy cow is between 41°F and 77°F. At temperatures above 77°F, cows have to use energy to cool themselves through heat loss via panting. As ambient temperature increases, it becomes more difficult for a cow to cool herself adequately.

Cows tend to stand rather than lie down and seek shade in hot weather. It’s common to find heat-stressed cattle standing in mud or the shade. As body temperature rises above 102.5°F, cattle eat less. They’ll be panting to cool down in order to compensate for limited sweat glands, increasing their respiratory rates.

Cattle also eat less often and during cooler times of the day, but consume more at each feeding, which can lead to acidosis.

Since milk consists of 87 percent water, hydration is the best place to start managing heat stress. High-producing cows may drink up to 50 gallons of water per day in hot temperatures. In fact, water consumption can double when temperatures rise, so make sure plenty of cool, fresh water in clean tanks is available to cows. Cooling fans or misters are also helpful to reduce cows’ body temperatures.


High-producing cows are also more sensitive to heat stress because of their high feed intake. Dry matter intake (DMI) starts to drop (8 to 12 percent), and milk production losses of 20 to 30 percent (which may exceed 10 to 25 pounds per day) occur when temperatures exceed 90°F. It is imperative to maintain intake in order to minimize these production losses.

Feeding direct-fed microbial (DFM) products can help aid digestion, improve feed utilization and keep dry matter intake up during hot weather. Good-quality DFMs provide high levels of microorganisms, including rumen/intestinal origin bacteria and digestive enzymes. Some DFMs include yeast, which provide enzymes and B vitamins and help maintain intake during hot weather.

When feeding DFMs, it’s important to maintain the viability of the live microbials, especially during hot weather. Producers should look for DFM products packaged in foil-lined bags or pouches that provide a better moisture barrier than regular plastic or paper. Packages should be kept closed or resealed between feedings to maintain microbial integrity.

Electrolytes, adequate ventilation, fresh water and proper feeding work together to reduce the effects of heat stress. Other heat management strategies available to producers are listed below.

• Provide plenty of cool, fresh water.

• Clean water tanks.


• Keep cows shaded if possible.

• Use proper ventilation.

• Use misters, sprinklers and/or fans.

• Balance ration for actual DMI.

• Add some water to the total mixed ration (TMR).

• Feed during cooler times of day. PD

References omitted but are available upon request at ­­
—Submitted by the author

Bill Zimmer
President of Bio-Vet Inc.