HEAT STRESS – The Hot Topic That Turns Dairies into Meltdown Mode :: The Bullvine - The Dairy Information You Want To Know When You Need It

I am really excited because you are actually starting to read this article on Heat Stress. At The Bullvine, we know that the frequency of Heat Stress articles might work against your decision to read one more. The normal reaction would be to say, “Oh yeah. I know Heat Stress like the back of my hand.” The problem is we have all heard about it. We agree with the idea of dealing with it. But, have we eliminated the effects of heat stress from our dairy herds? No.

The facts tell different, but likewise oft repeated, stories of failure. Reduced feed intake. Less milk production. Lower butterfat percent. And, topping the list, poor or even stopped reproductive performance!

Knowing heat stress is not so much about learning to know it like the back of your hand. It’s more like fighting to keep it from slipping to the back of your mind.

We all know what it’s like to try to work in extreme conditions. Or do we? Recently a friend was called for Jury Duty. No problem. Well, no problem until the AC in the courthouse failed, and everyone there spent the morning with no relief from the rising heat or the increasing stress. Long story short. Later that night, there was an emergency trip to ER and much concern about heart, lungs and respiration. The verdict. Don’t ignore the signs of heat stress.

If You’ve GOT HEAT, you’ve GOT STRESS!

Coming from Ontario, Canada or areas of the Midwestern USA, we might have only six or seven days of excessively high heat occurring one or two times during the summer season. But, even if it isn’t extended as it is in many southern states, it is important to remember that cows start to be stressed at sixty-eight degrees Fahrenheit or 18 degrees centigrade. When the outdoor temperature is above 80 degrees (27 degrees Centigrade) for extended periods, problems turn into high-risk situations. This is where the good managers are separated from everyone else. They don’t settle for losses. They don’t aim for mediocre.

Do You Know the EARLY Signs of Heat Stress?

Of course, if cows are panting rapidly or going down, you can be sure they are at risk. But long before the obvious signs of crisis, cattle are beginning to suffer from heat stress. Continuous hot days and nights don’t provide any break in the cycle of high temperatures and cows quickly stop eating in an effort to reduce the heat coming from rumen fermentation. One thing leads to another. Less feed in the rumen means less fermentation. Along with less volatile fatty acid production, there is a reduction in rumen microbes and metabolizable protein. This reduction in feed intake reduces milk production by more than 10% or down as much as a gallon or more per cow per day. Heat stress also reduces the butterfat level (0.2-0.3%). These conditions now open the door to other health issues, including reduced reproductive performance.

Reproduction Declines as Heat Stress Rises

There is a direct correlation between heat stress and fertility. A three-year US trial reported on the winter to summer drop in confirmed pregnancies. In winter 30% were confirmed, results dropped to 10 to 15% in summer.

Be Alert to the Ongoing Heat Stress Effects

As mentioned, reduction of feed intake is an automatic response by cows suffering from heat stress. Several points should be noted about the effects that this produces:

Digestion of forages causes more heat accumulation than the digestion of grains.
Animals on a higher forage ration are more inclined to heat stress than animals on higher grain
Cows will sort vigorously to eat more grain than forage.
Early lactation and higher yielding cows are the first to be affected.

It is good management to be alert to these signs when they occur in the cattle we care for. Careful observation of the condition of the feed in the feed bunk is an absolute must do.

Once into a cycle of hot days and nights, cows experiencing severe heat stress, produce less milk. In extreme cases, death from heat stress can occur.

What Can Be Done? What Must Be Done?

There are three main areas to consider when trying to relieve bovine heat stress. First look at the exterior sources of heat. Then consider what can be done to affect heat producing digestion. Finally, look for opportunities to provide direct and indirect cooling of the cows.

Under the Sun: It seems almost too obvious to say that we must be aware of direct solar radiation from the sun. Whether your cows are on pasture or in the barn, it is important to do what you can to moderate exposure to extremely high temperatures. Many dairy cattle are dark colored and this too raises their susceptibility to heat stress. Out of doors make sure that cattle have access to shade and fresh feed and water. Watch out for wet conditions that can add high humidity to the risks coming from high temperatures. If the outdoors isn’t an effective solution, keep cows in the barn.
Inside the Barn: Getting proper air flow around the cattle in the barn will make a huge difference in cow comfort during excruciating weather conditions. Set up the maximum natural ventilation, preferably cross ventilation, and use fans to effectively increase air flow.
With the air moving then turn your attention to ways to use water to cool the air and the cows. A fine mist will work to cool the air and thus make it easier for cattle to breathe. In addition, it might be necessary to provide direct wetting of the cows. This will enhance evaporative cooling on the skin surface of the cows. Once again, too much wetting is not necessarily better. You don’t want to have so much water that it washes off the teat dip, wets the bedding or raises the humidity to unacceptable levels. It is especially important to avoid overcrowding! A reduction in cows could have a positive effect on the production of the remaining cows. This solution could offset the losses in milk production caused by overcrowded, heat-stressed
At the Feed Trough: Work with your feeding team and nutrition consultants to provide a ration that include high quality, highly digestible forage. Feed your highest producing cows the best quality feed. Consider formulations that involve using fat to maintain energy intake during declining feed intake.
In the Milk Line: Little adjustments in all areas of the dairy cow day have the potential to reduce heat stress. If it is an option, increasing milking frequency might be one way to moderate heat stress. 3x milking means less heat stress, particularly on heavily producing cows.

The Bullvine Bottom Line

Managing heat stress in cows is up to you. Don’t procrastinate. Reduce exposure to the environment. Take direct steps to keep cattle feeling cool. Use ration formulations that reduce as much as possible heat from metabolization. Don’t accept meltdown. Keep good records. Keep your cool.