Proactive steps to beat heat stress

Carole Curtis
Now Media Group


The true cost of heat stress is inked in red at Kansas State University, where the K-State Dairy herd, with its' nearly 32,000 pound rolling herd average, takes a big hit every year.

'We've got some issues with our old facility and It costs us every summer, very dearly,' Dr. Michael Brouk, Kansas State University, said during the March 'Hoards Dairyman' Industry Webinar.

The program, 'The Latest on Beating the Heat,' was co-hosted by Steve Larson, Hoard's Dairyman, and Dr. Mike Hutjens, University of Illinois, and sponsored by Dairy Nutrition Plus.

In 2014, milk production at K-State Dairy bottomed out in October. In 2013, it was August. 'We're back into December before we climb back out of that dip,' Brouk shared.

If Wisconsin milk producers aren't doing something to alleviate heat stress, they should be, the dairy specialist said, citing studies a related economic loss of $72 per cow per year here. 'That's a lot of money on the table,' he said.

Heat stress causes impacts on the cow that last beyond the dog days of summer. Along with decreased milk production, it increases the number of days open, decreases immune function and fertility, and leads to increased culling.

Research on conception rates of cows kept cool (body temperatures below 102.2 degrees) and cows without cooling systems (body temperatures over 103.1 degrees) revealed 'dramatic differences' in pregnancy rates. 'Cooled cows have huge advantages over noncooled cows,' Brouk pointed out.

Factors of heat stress

Dairy farmers need to be concerned about heat input, the metabolic heat the cow herself produces and air temperature, as well as heat exchange. 'The whole goal here is how can we increase the productivity of our animals,' Brouk said, citing studies detailing a 12-15 percent drop in milk production for heat stressed animals.

A dairy cow runs hot. She produces about 4,500-5,500 BTUs an hour, equal to 16 100-watt lamps burning. A lack of heat exchange leads to increased heat storage, which increases body temperature.

'That's why her body temperature rises when she's heat stressed,' Brouk observed.

Cows have four different methods to exchange heat. They can evaporate it away by panting and sweating, radiate it off their bodies, and conduct it away by laying down in damp areas or in water. Heat can also be removed by convection — the movement of air across their bodies.

Considering the efficiency of the various options, the focus should be on cooling the cow, Brouk said. The primary way is evaporative cooling from the outer body surface.

Watch the THI

By using the THI (temperature/humidity index), the cooling requirements of a dairy cow can be estimated and the data used to improve cooling strategies to alleviate heat stress. For example, if it is 84 degrees F and 21 percent humidity, the THI is 73.

Brouk pointed out that the updated THI threshold for a cow giving at least 77 pounds of milk/day is 68 THI units. 'When the THI is over that, there will be a loss of 4.85 pounds of milk per day for every 24 hours,' Brouk said. 'Maybe we need to think about cooling cows down a little sooner than we have in the past.'

How long the heat stress lasts is an important factor. If it goes on for days into weeks, the impact becomes greater. Intensity is also important, in terms of the hours the heat stress is experienced and if the cows are able to cool down during the night.

Cooling systems

For systems that combine airflow and water on the skin for heat loss, Brouk noted that as airflow or wetting cycles increase, heat loss from the skin increases. While HVLS (high volume low speed fans) move lots of air, he noted, they do so at a low speed, whereas basket-type fans can move air faster.

'We are a little concerned about air speed,' Brouk said. 'With the lower speeds, you're giving up some of the ability to reduce heat.'

Brouk recommended considering the cow's activity schedule, which typically involves 12-14 hours of laying around, five hours of eating and 2.5-3.5 hours for milking. 'Think about where she is, what she's doing and how you can eliminate the heat there,' he advised.

Feedline systems that utilize airflow and skin soaking work really well. The cows can be soaked for 30 seconds every 15 minutes, every 10 minutes or every five minutes. It is important to use soaking, followed by fans, and go in cycles to utilize water efficiently, Brouk noted.

However, there are challenges with feedline cooling. Only 25 percent of the sprayed water touches the cow and she spends only 12 percent of her time at the feedline.

Given the vast majority of a cow's day is spent resting in her stall, dairies can zero in there, but it should be done efficiently. 'A lot of barns just blow hot air over hot cows. It really doesn't do much,' Brouk said.

One solution might be linking the soaking system with feeding and push-up, perhaps by running the system for 1.5 hours after milking and then again four hours later. It depends on the routine on the farm, he noted, but shutting the system down for intervals can cut water usage substantially.

A sensing system to detect cows at the feed bunk is also a possibility. 'The goal is improved water utilization,' Brouk pointed out.

Airflow and cooling

Studies show cows need airflow in the freestall area and on feed lines, but placement can also be challenging. Too much distance between the cow and basket fans reduces the potential effectiveness of the fans, but bringing them down and adding more can place them too close to the cows, lead to equipment blight, the need for multiple rows of fans and excessive fan noise.

One possible solution is the newer, larger fans that employ louvers to direct much larger volumes of air down onto the cows where they really need it.

'We can usually get these fans located closer to the cows and more effectively cover a larger area than some of our basket fans do,' Brouk said.

While water can't be sprayed on cows in their stalls, there are some systems that offer high pressure mist. Although maybe not as effective as a direct spray, such fogging systems cool the air for a refreshing air flow over the cow.

Evaporative cooling

In addition, systems using evaporative cooling through cellulose pads and fans are becoming increasingly popular.

K-State Dairy built a lean-to shed onto its dry cows' bedded pack barn and uses an evaporative cooling system with fans. The pads run from 8 a.m. to 10 p.m. The impact has been a significant decline in air and internal temperatures. 'This is a good way to reduce some of the body temperatures we see on dry cows,' Brouk said.

Research has found that cooling dry cows is a profitable option. 'I encourage you to look at the data. It shows pretty convincingly that cooling dry cows is worth a lot of milk,' he pointed out. 'We need to pay more attention to that with some of the systems that we have.'

In the future, Brouk believes there will be increased interest and use of evaporative cooling. The key is to concentrate on controlling moisture and running the system only when appropriate.

Cooling is also 'really, really' important when cows are standing in the milking parlor holding pens, Brouk said, but high production groups and pre-fresh cows also benefit from cooling. 'Sometimes evaporative cooling in the milking parlor is good, too, for the comfort of the cows and the workers,' he said.

Helping dairy cows ward off heat accumulation will lead to increased dry matter intake, higher milk production and better reproductive rates.

'Overall, if we can improve breeding and milk production during the summer, hopefully, we should be able to improve the profits on our dairy farms,' Brouk said.