The Long-Term Ramifications of Heat Stress on Dry Cows

August 26, 2020

At VES, there are few aspects of cow care that fester in our craw more than ignoring the impacts of heat stress on dry cows. It’s a critical period in a cow’s lactation cycle that deserves every ounce of care and attention as all others and can have long-term implications on a herd if ignored.


Dry Cow (n.) – A late gestation, non-lactating cow. Often considered an afterthought of the dairy world. The dry period lasts for roughly 45 to 60 days.


Here are a few reasons why:


Financial Tunnel-Vision

Since Dry Cows aren’t producing milk (and revenue!) to the operation during their dry period, they can become an afterthought, leaving them relegated to second-rate facilities in comparison to lactating animals. These secondary living quarters, in some cases, are missing proper ventilation and cooling strategies, leaving dry cows susceptible to heat stress.

Coincidentally, by relegating dry cows to less-than-optimal living environments, dairy producers may actually be losing more milk here than during any other period during the cow’s lactation cycle. (More on that shortly.) 

At VES, we work hard with our producer partners to develop specific heat abatement solutions based on the design and environment of the dairy to minimize heat stress risk, even during the hottest months.


Ignoring Udder Development

During a cow’s dry period, she is adding secretory cells, which are the cells that produce milk, to her udder. The more secretory cells, the more milk the cow can produce. Relatively, a cow has the most secretory cells at the time of calving. This is critical to remember when considering that heat stressed cows will often deliver their calves between two and eight days early, meaning that that cow has less time to develop secretory cells than if she had calved at full term.

Studies from the University of Florida have found that heat stressed dry cows, on average, produce between 5 and 16 pounds less milk per day for her entire lactation than cows that lived in environments with proper heat abatement solutions implemented in their quarters. See the chart below for a comparison of the cows studies in the University of Florida trial.


University of Florida study showing heat stressed dry cows, on average, produce between 5-16lbs less milk/day



In the upper Midwest, where heat stress risk can extend for three months or more, roughly 25 percent of a dairy’s herd could be susceptible to missing out on potential production if proper heat abatement strategies aren’t used.

What would missing out on additional production of five pounds of milk per day per cow across a quarter of your herd look like? How about 16 pounds? That’s a lot of potential missed production to consider.


It’s About What Comes Next

In a perfect world, dairymen would see dry cows for exactly what they are: a population of the herd preparing to enter a high-risk, but also a high-production period of their lifecycle.

After calving, all cows are already susceptible to weakened immune function. However, those animals that experience heat stress during their dry period experience even further impairments, putting them at higher risk of developing mastitis, metritis, pneumonia, and other diseases.

In another University of Florida study, again using soakers and fans, researchers investigated the ability of a cow’s white blood cells to consume (phagocytosis) and kill (oxidative burst) disease-causing bacteria. The study found that cows that were cooled had better immune function after calving and returned to a healthy state post-delivery. See the chart below for findings on immune function between cooled and non-cooled dry cows.


University of Florida study findings on immune function between cooled & non-cooled dry cows



Finally, calves born to heat-stressed dry cows showcased lower growth rates, poorer reproduction performance, and less milk production in their first lactation compared to calves born to dry cows with proper cooling. Experts believe this is due to epigenetic silencing, which means that certain genes that help with growth and production are suppressed to help the animal deal with heat stress during the postpartum period, and beyond.


Epigenetic Silencing (v.) – The act of a calf’s genetic sequencing being altered to prepare the calf for entering a hostile, heat stressed world. Often, developmental resources are shifted to areas to help the calf survive, rather than growing or producing. The impacts are lifelong.


What You Need to Remember:

 Heat stressed dry cows produce between 5 and 16 fewer pounds of milk per day post-partum, than those who are properly cooled.

– Use long-term thinking when considering Dry Cow living environments. They deserve the same kind of animal-centered ventilation and cooling features as your highest producing animals during the same period.

– Heat stressed dry cows produce less, have impaired immune function, and give birth to lower-performing calves.

– Proper cooling of dry cows has far-reaching effects on a dairy and should always be discussed as a vital area of importance with dairy producers. 

  Connect with VES dairy experts who can examine the climate and weather patterns in your geographic area to help determine which heat abatement strategy is both cost effective and cooling efficient for your operations and your animals.





Information adapted from: Elanco Animal Health. Bailey T, Sheets J, McClary D, Smith S, Bridges A. Heat Abatement Guide. 2016.

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