Heat-Stressed Dairy Cattle

By Dillon Snell

With summer now under way, heat stress is beginning to have an impact on most Northeast dairies. Although heat stress in herds hasn't become a detrimental issue thus far in the season, it will only be so long until the rain and cool temperatures we have been encountering fade away and our well-producing herds begin to see milk yield levels decrease. Generally it's a simple task to pick out a severely heat-stressed cow, but at what point does heat stress begin affecting production, and how can a producer impact this situation?

In all reality, a high-producing dairy cow could experience mild heat stress with an environmental temperature as low as 68 degrees Fahrenheit. This mild heat stress could result in production loss, as well as negatively impact milk components. Dairy cattle are more susceptible to encountering heat stress than most other animals because of the heat generated from fermentation in the rumen. A dairy cow's rumen is comparable to its own internal furnace that burns all year, so moderately warm temperatures with some relative humidity can have detrimental effects on production.

Heat stress in New York starts to show up in the month of May. Following are some signs a producer can look for while walking through the herd.

First would be a decrease in dry matter intake. Heat-stressed cows will not consume as much feed as cows that are not stressed, so if you notice that an abnormal amount of your cattle are avoiding feed bunks at times they generally eat, it's likely your herd is enduring some heat stress.

Next, check standing times. If a large percentage of your herd is standing, either in stalls or feed alleys, they are attempting to cool themselves by allowing air to flow under them. Many cows may also begin perching - standing with their front feet in the stall and their rear feet in the alley behind the stall. Perching can be a sign of inadequate stall size, but it may also be an attempt for cattle to lower body temperature themselves by having more body surface area cooled by airflow. An increased amount of lameness may occur in the herd as a result of cows not getting a sufficient amount of resting time due to the extended period of time standing.

More severe symptoms of heat-stressed cattle would include faster respiratory rates and heavy breathing, which is noticeable behind the upper rear ribs in the hip area. Count the number of breaths your cow takes; if she is in the range of 80 beats per minute or more, she most likely has a core body temperature of 103 degrees and is heat-stressed. In extreme cases of heat stress, cattle will begin panting like dogs, and drool will foam from their mouths. If you witness this, don't automatically begin spraying the cow down with cold water, as it could send the animal into shock. Remember, once a cow's core body temperature reaches 108 degrees, it will most likely result in death.

There are numerous strategies that can aid in the battle against heat stress. Limiting overcrowding in groups and pens by pasturing heifers and dry cows will help lower barn temperatures. Also try creating more lactating groups to limit the amount of time a cow spends in a holding pen. This change will decrease stress levels in the herd. For example, instead of sending a group of 80 cows into the holding pen, make two separate groups of 40 cows. Unless it's tunnel-ventilated, your barn's windows and side curtains should be removed and opened up to promote maximum ventilation. If manageable, try to change feeding times to a cooler time of the day, such as early morning and late evening. Cattle will be encouraged to eat more if they aren't trying to combat the heat during feeding times.

Although these are all effective methods of preventing heat stress, the best way to lower cattle's core body temperature is evaporative cooling. That's the effect you feel when the wind blows on you just after getting out of the pool. In order to develop an evaporative cooling system in your barn, all you need is water and air movement. Placing misting sprinklers and fans over feed alleys will not only prevent heat stress, but it will also encourage intake and ultimately production by making the feed bunk a cool, pleasant place for cattle to be on even the hottest days. Another key place to incorporate an evaporative cooling system is in holding areas before cattle are being milked. Water tubs should also be checked, cleaned and inspected daily, as a cow's water intake could nearly double when heat-stressed.

In order to protect your herd from the effects of heat stress this summer and maintain profitability as well as production, make your best efforts to keep your cattle cool and drinking plenty of water. Transition them to a summer ration a few weeks ahead of time, not after the arrival of high temperatures. Adequate water sources are the most influential factor in milk production year-round. Along with production, water is a key contributor in maintaining a standard body temperature in cattle, so make sure you keep your cows drinking frequently with free-choice watering systems. It's understandable that this time of year is the busiest as we try to manage all our crops, but if we can take the time to make these changes in our herd, we will see improved herd health, production levels and profitability.

Dillon Snell is a student at the State University of New York at Cobleskill, majoring in dairy management and production.