Summer is just around the corner and with it high temperatures, humidity and heat stress. According to a 2019 Foundation for Food and Agriculture Research study, the U.S. dairy industry experiences $1.5 billion in losses annually due to heat stress.

Morris preston
Technical Service Specialist / Diamond V
Regional Sales Manager / Diamond V

Higher temperatures can affect herds, and in turn, decrease performance, production and profit.

When animals experience heat stress, typical outcomes include the following:

  • Dry matter intake (DMI) may decrease.
  • Milk production may decrease 3-7 pounds from June through August, directly impacting cash flow.
  • Increasing temperatures along with high humidity can cause bacterial populations to surge, resulting in rising somatic cell counts.
  • Butterfat can potentially drop due to heat-induced metabolic effects, including subacute ruminal acidosis (SARA) and leaky gut syndrome.
  • Conception rates can decrease.

With summer quickly approaching, your cows will soon be feeling the heat. Heat stress impacts more than just the milking herd. Dairy producers should implement a whole-herd heat stress solution to limit production impacts. Here is how you can help your herd stay happy, healthy and productive.

Heat stress levels and effects on the body

Lactating: When it comes to lactating cows, heat stress has the greatest short-term impact. An effective strategy is to use evaporative cooling to cool cows’ internal temperature. Higher temperatures can negatively affect milk production and milkfat yield due to decreased DMI, decreased meal intervals, subacute rumen acidosis (SARA) and leaky gut syndrome. Although it is vital to provide proper heat abatement strategies, feeding tactics may also help in reducing performance loss.


It is common for feed intake to decrease during hotter months. When cows eat less, this will lead to decreased milk production. To help prevent decreased intake, make sure they have constant access to fresh feed. Feeding more frequently during cooler parts of the day keeps feed fresh, flavorful and can increase intake.

Incorporating effective feed additives could help promote gut health, immune strength and overall wellness. Healthy cows perform better, and a healthy gut can help cows manage the heat. Ultimately, this can result in greater profitability on the farm. Consult with your nutritionist about what ration changes might be appropriate for warmer temperatures, including the addition of products to optimize rumen health.

Another beneficial idea is to conduct a total mixed ration (TMR) audit. This is a systematic approach to measuring the operational efficiency of a dairy’s feeding system. Today’s TMR audits can detect inconsistencies in the ration and help identify other feed-related management opportunities. The ability to deliver a consistent diet day after day, week after week and month after month is an important goal for nutritionists and producers because ration consistency directly affects the operation’s bottom line. Consistent diets support a healthy rumen, which allows other body processes to function well so the cow experiences optimal health, reproduction performance and milk production.

Dry cows: Reducing or preventing heat stress is vital in order to support DMI and milk production in lactating cows. However, dry cows also suffer challenges from heat stress, and the impact can affect generations to come. When a dry cow experiences heat stress, the body temperature of the unborn calf increases. This alters the calf’s metabolism and gene expression, which can lead to smaller calves being born, along with affecting the calf’s health and performance well beyond birth.

Research from of the University of Florida also shows that heat stress not only has a negative effect on the health of a dry cow, but it affects the next lactation and the resulting calf. This research also noted that dry cows exposed to heat stress suffered several setbacks in mammary cell development, which translated into reduced milk production in subsequent lactations. The study also demonstrated that cows cooled during the dry period maintained better bodyweight, allowing for better performance post-calving. In addition, calves born to cooled dry cows were heavier, healthier and performed better during their first lactation.

Remember these top five checklists to help your herds have a better chance of staying healthy and productive.

Top five checklist

Holding pen ventilation and cooling: Producers can use the respiratory rate of an animal to indicate heat stress. Anything above 80 breaths per minute is a sign of advanced heat stress. When it comes to the holding pen, you want a wind speed of at least 10 mph.

Push up feed: Make sure fresh feed is always readily available. This is extremely important during overnight hours.

Pressure on feedbunk soaker lines: Pressure on soaker lines should be 15 to 20 pounds per square inch (psi). If you see mist in the air, the water pressure is too high. The height of soakers needs to be 5-6 feet off cow platforms. Have a controller set for nozzles to run a certain amount of time on and off. It’s recommended that when the temperature is 70ºF to have the nozzle running for one minute on and 12 minutes off. For 82ºF, have the nozzle running for one minute on and four minutes off.

Check wind speed: Wind speed should be at least 7 mph anywhere cows congregate, such as feedbunks, stalls and holding pens.

Housing: Make sure every cow has a clean and useable stall. Cows make the most milk when they’re laying down; we want their housing to be as comfortable as possible.

Heat stress is inevitable. It not only affects the animal in the short term, such as reduced feed intake and milk production, but its impact can be felt for generations to come. Therefore, we need to take the right steps to help alleviate its effects. The management of heat stress is imperative when it comes to current and future animal health, reproduction, productivity and profitability.