Dairy Cattle & Stress: Don't Overlook The Dry Cows This Summer

Summer is fast approaching, bringing with it the promise of hot days. Benefits of cooling lactating cows are hard to deny with the plethora of data documenting increases in milk production and reproductive efficiency with the use of heat abatement systems. But what effect is the heat having on dry cows? These girls are exposed to the same stressful situations—often with shade trees as their only cooling provision.

What long term effects result from heatstressed dry cows? Heat stress in dry cows results in lower calf birth weights; reduced feed intake and magnified negative energy balance; suppressed immune function; and lower postpartum milk production. Lower calf birth weights are shown to be correlated with reduced early lactation production. Additionally, calf survival can be compromised with lower birth weights and poor colostrum quality from cows with suppressed immune systems.

Mixed results have been observed for reproduction, with some studies finding reduced conception rates for summer calving cows while others found no difference. A 1999 study in Texas observed 21% conception rates for summer calving cows versus 36% for fall calving cows. A recent study from a commercial herd in California found increases in milk production of three pounds per cow per day with use of fans, sprinklers, and shade in the dry period versus sprinklers only. This three pound increase netted an additional $2,100 for this farm annually.

Cooling systems for lactating cows should be the first priority, followed by heat abatement for dry cows. Early lactation production and health sets the stage for the entire lactation. Cooling for dry cows is worth considering if it can help these cows get off to a good start in lactation. The logical area to target is the dry cow feed bunk. Reduced heat stress in this area will encourage cows to eat more. Dry cows are prone to reduced dry matter intake in the week prior to calving regardless of season, leading to increased negative energy balance and immunosuppression.

Increasing intakes ensures adequate energy for fetal development, enhances immune function, and prevents many metabolic problems. At a minimum shade clothes over the bunk should be considered. Ideally fans and sprinklers should be incorporated as well, with fans every 24 - 30 feet. However, this requires electricity at the bunk and the ability to handle runoff from sprinklers. Sprinklers would not be prudent with a drylot feeding area.

The added stress of negotiating through the mud created would expend more energy and discourage intakes, defeating the purpose for cooling in the first place. Carefully evaluate your dry cow lot for cooling options. Your local Dairy Extension Agent can provide recommendations for your individual situation.

Remember, cows experience heat stress when the temperature-humidity index exceeds 75°F. Temperatures have already exceeded this threshold, so NOW is the time to get these systems in place.

By Beverly Cox, Extension Agent, Franklin County
Dairy Pipeline Newsletter - Virginia Cooperative Extension