I’m not sure who sent the stray voltage to the groundhog in February, but I think he was a little off-target this year. While spring yielded to summer early in the South, Old Man Winter clung to some parts of the country when the May flowers were supposed to arrive.

However, one thing is certain: The dog days are here for a while.

No matter if the summer heat came about rapidly or early and is staying longer than you like, a lactating cow herd can take a beating as the thermometer rises. In the absence of disease, when cows have clinical signs such as increased respiratory rates and open-mouth breathing, it’s evident they need relief. Preventing those clinical signs is imperative for continued herd health.

While you may be monitoring the temperature-humidity index, let’s examine a few other heat stress components and opportunities to alleviate the discomfort.

1. Cooling with water: While cows don’t plan a summer trip to the beach, they may have opportunities to appreciate a nice cooling pond in some regions of the country. But don’t throw caution to the wind: If not maintained, holding ponds can potentially contribute to mastitis and leptospirosis if the herd is not vaccinated.


Evaporative cooling can also be an effective method to alleviate heat stress. During the summer, misters and fans in barns with adequate roof height and overall excellent air flow would be a top choice of relief from the sun’s radiant heat.

2. Adequate air flow: Air flow is a top concern when designing a barn or adding on to existing structures. Dairy producers should consider physical barriers that might restrict air flow and determine if they can be eliminated. For example, questions like “How close is the next building?” or “Is the proximity of the tree line on the neighbors’ property too close, which could create ‘wind shadows’?” should be asked. Reducing wind shadows allows for better air flow in the surrounding area.

Another option to provide consistent cow comfort and minimize losses to heat stress is to build a tunnel-ventilated barn. In a tunnel barn, evaporative cooling is enhanced by consistent air flow with numerous fans at one end drawing air through the barn. The air can be cooled by high-pressure jet misters at one end, which atomize water, resulting in evaporative cooling or with sprinklers mounted strategically to drop water directly on the cows’ backs and flanks.

3. Clean, fresh drinking water: This next tip may sound like a no-brainer, but it is too important not to mention. It is imperative there is ample clean, fresh water available to cows, as water consumption plays a vital role in staying cool. Therefore, if there’s ever a time to pay attention to prevent overcrowding, the summer is it.

Cow crowding can create wind shadows by impeding air flow at the ground level. Consequently, the temperature in barns with inadequate air exchange rates will increase, and with limited availability of water troughs or misters, cows may lose one of their most effective means of heat control: water consumption.

4. Ration adjustments: Altered feed intake patterns may exist during times of heat stress, such as slug feeding or even reduced feed intake. Changes to the ration may be necessary to increase the energy content with consideration to use high-fat feeds (whole cottonseed, tallow or bypass fat, roasted soybeans) while reducing grain.

Pay attention to the protein source as well, and make adjustments to balance the ration for minerals. Be sure to consult your nutritionist and veterinarian regarding options for any ration changes.

Lingering effects of heat stress

When the investment in cow comfort is made, the return in increased milk production can be substantial. Heat stress may reduce milk production by up to 50 percent in high-producing cows. One reason for decreased milk production was noted in a recent study comparing mammary biopsies of heat-stressed and cooled cows during the dry period and into early freshening.

The heat-stressed cows had decreased mammary cell proliferation, suggesting less functional mammary cells at the onset of lactation, which then compromises subsequent lactation performance.

Another area widely impacted by heat stress is fetal health. Dry cows that experience heat stress produce calves with lower birthweights, weaning weights and a compromised immune transfer, not to mention reduced first-lactation milk production in heifers born during times of heat stress.

Lower production from heifers of heat-stressed cows was shown to be almost 11.22 pounds per day less than heifers born to cows which were not heat stressed. This daily loss amounts to almost 2,750 pounds over a 35-week period.

While those of us who live in the South can’t totally escape heat stress, the investment made to keep cows cool can provide a significant return on investment during lactation and beyond, no matter where you reside.  end mark

PHOTO: Heat stress takes a lasting toll on dairy cows. Cut down on its negative effects by providing cooling, adequate air flow, plenty of drinking water and altering the ration for proper nutrition. Photo by Mike Dixon.

References omitted but are available upon request. Click here to email an editor.

Andy Bennett is a professional services veterinarian with Boehringer Ingelheim. Email Andy Bennett.