It’s almost a surefire guarantee that the Northeast will get hot and humid at some point this summer. That means your dairy herd is going to get stressed. In another year with low milk prices, the last thing you need is to see your milk production disappear when it gets hot. When managing heat stress, controlling your cows’ environment is the first priority. Any changes in feed management and nutrition will be much more effective in situations where the cows can be kept cool and comfortable.

Dairy cows produce a lot of internal heat and naturally tolerate cooler outdoor temperatures much better than high ones. Cows are most comfortable in a temperature range of 40 degrees and 50 degrees Fahrenheit and, as long as the humidity remains low, will remain comfortable even into the 80 degrees Fahrenheit range when not in direct sunlight. However, many U.S. locations see daytime temperatures exceed 100 F for extended periods during the summer and many more will experience both high humidity levels from 60 to 100 percent along with temperatures above 80 F. These extreme conditions will quickly reduce feed intakes along with milk production and health.

Know Your Cows’ Summer Requirements

Before you begin changing the ration, however, you must make sure your cows have an unlimited supply of cool, clean water all summer long. When it’s hot and humid this single item will go farther than anything else in reducing heat stress and milk production losses. After that, from an environmental management perspective, focus on evaporative cooling with body sprinkling and good air movement with the generous use of fans if possible. Avoid over-crowding in wash pens and feeding areas. If your cows spend a lot of time out of the barn during the summer, make sure they have access to water and provide shade to get them out of the direct sunlight for part of the day. Consider these other important facts regarding environmental heat stress:

  • If the temperature in your cow’s environment is over 80 F and humidity is over 30 percent you need to start cooling things down.
  • When the temperature climbs over 80 F in high humidity a cow’s feed intake has decreased by 8 percent to 12 percent or more – meaning there’s less nutrition for milk production.
  • When the temperature is 90 F or higher, milk production has decreased by 3 percent to 20 percent or more and conception rates can be as low as 0 percent.
  • Cattle sweat only 10 percent as much as humans.
  • Panting can increase the cow’s metabolizable maintenance requirement by 20 percent.

Manage Nutrition When It’s Hot

There are a number steps we can take to manage nutrition during the hot summer weather. The main feeding challenge during hot weather is to maximize energy intake, while maintaining ration fiber levels and proper rumen health. Maintaining a balanced ration can be difficult because:

  • Feed intake drops.
  • Cows prefer grain to roughage in hot weather, which can lead to rumen acidosis.
  • If forage quality is variable, sorting may occur.
  • Cows that freshen in extreme heat and humidity are much more susceptible to metabolic problems such as displaced abomasum (Das) and ketosis as a result of poor feed intakes.

A feed ration that’s formulated to support 85 pounds of milk in the cooler spring weather will not support that much milk when it gets hot and humid. When heat and humidity are excessive a cow can reduce her dry-matter feed intake by 5 pounds. This drop in nutrition can correspond to a decrease of two gallons of milk when the temperature soars to 90 F and humidity is at 80 percent. Energy density in that ration needs to be increased significantly. If a feed ration is not adjusted to account for the reduction in dry matter intake, nutrient intakes will be depressed and body conditions will also suffer.

herd of cattle drinking water
When managing heat stress, controlling your cows’ environment is the first priority.Photo Courtesy: steverts/istock 

Handle Heat Stress With Ease

Low fiber levels can lead to rumen upset, which often will further reduce feed intake. Trying to compensate for reduced energy intake by adding more grain to the ration may only compound the problem. Along with that, when a cow pants excessively she’ll drool large amounts of saliva, losing potassium and sodium that are necessary for rumen buffering and other metabolic functions. Here are some nutritional guidelines to help manage nutrition during heat stress:

  • Feed high-quality forages but keep the physically effective NDF (peNDF) more than 20 percent or rumen health will be affected.
  • Keep the rumen buffered with sodium bicarbonate especially if the effective fiber levels decrease through increased grain consumption.
  • Potassium is critical in maintaining proper acid-base balance during periods of extreme heat. Maintain potassium at least at 2 percent of the total ration. When potassium levels are increased, magnesium must also be kept near 0.4 percent of the ration, as well. Research has also shown that increasing potassium levels can increase dry matter intakes.
  • Provide most of the ration during the night or cooler periods of the day.
  • Add extra water to the total mixed ration (TMR), silage or haylage if dry matter intakes drop seriously. This can encourage cows to keep eating.
  • If possible, feed ensiled feedstuffs more frequently to compensate for shorter bunk life during hot weather to prevent heating and spoiling. Keep the feed fresh in the manger or bunk.
  • Adjust both energy and protein densities when dry matter intakes decrease.
  • Feed a rumen protected fat as opposed to increasing starch or tallow to increase the caloric density of the ration.
  • Feeding a yeast product has been shown to improve fiber fermentation and dry matter intakes.

Reproduction problems can crop up after prolonged periods of heat stress as well. When cows are heat-stressed, metabolic and hormonal changes prevent them from cycling normally and conceiving. It’s well known that both short-term pregnancies can be aborted and ovarian follicular development will be affected preventing conception as long as two months after the period of heat stress.

There’s nothing more discouraging on a dairy farm than seeing the cows suffering needlessly and dropping in milk production. Having a plan in place for cooling your cows during the summer heat and humidity will save money in the long run. Planning for it early in the season will save milk when the heat and humidity finally hit. There’s nothing we can do to stop the heat, and we can never make the summer heat and humidity go away, but we can do our best to manage around it.

Cover Photo: steverts/istock