Cow cooling is not just about fans and sprinklers. Science, technology and even genetics can all be part of a dairy’s heat-abatement strategy. Earlier this year, industry leaders traveled around Puerto Rico and the U.S. with the Heat Stress Road Show.

Dairy cow heat-abatement experts Dr. Todd Bilby, Merck Animal Health, and Dr. Pete Hansen, University of Florida, shared new tools and technologies that can be used to assess heat stress as well as alternative opportunities to reduce the negative impacts of summertime temperatures.

Existing technologies for heat-stress evaluations

Cows tend to stand for longer periods of time as temperatures rise, which elevates their stress levels, too. Activity monitors can be used to tell when the herd is experiencing this. These devices are becoming a popular heat-detection tool on dairies.

As Hansen pointed out, if the investment has already been made in this technology, using the data to assess levels of heat stress can be a cost-effective option.

Checking rectal temperature is also a way to observe heat stress. However, taking temperatures this way is time-consuming; further, body temperatures may be elevated as the cow is restrained to collect the data.


Instead, temperature launchers can implant controlled internal drug release (CIDR) devices to check vaginal temperatures. Taking temperatures on intervals can help monitor when the herd is getting heat-stressed.

After the device is removed, the information can be downloaded and the data can be plotted. Using this information, producers can pinpoint the times when the herd is suffering from heat stress.

Smartphone apps

With smartphones being so common, apps can be another addition to a heat-stress abatement program. “The apps are designed to replace the heat-stress charts in the barn office and put the information on a smartphone in the hands of the producer,” Bilby said.

Having these assets at their fingertips will help producers make appropriate and timely decisions on when to alter heat-stress devices such as fans and misters.

The ThermalAid app created by the University of Missouri gives a great look at heat-stress levels using either temperature or humidity data from the local weather station, or this information can be manually entered and will give the current range of heat stress.

For the most accurate results, the app can be customized to reflect conditions such as if the herd is grazing or confined and if it is a healthy or sick pen. ThermalAid also has a feature to calculate the respiration rate for additional data.

The Cool Cow app is one more tool that can evaluate heat stress levels. Produced by Purina Animal Nutrition LLC, it contains an easy-to-use heat-stress calculator. Once current temperature and humidity levels are entered, the severity of heat stress is given.

From this, the app suggests changes that can be made through management and nutrition to help decrease the effects of the heat.

A benchmarking tool

The summer-to-winter (SW) ratio, developed by the Extension Service of the Ministry of Agriculture and Israel Cattle Breeders Association, is an assessment tool for evaluating the effects of heat stress on commercial dairies.

SW is simply a comparison of parameters like pregnancy rate, conception rate and milk production averaged over the three-month periods of July through September (summer) and January through March (winter).

The resulting figures are divided to find the ratio that can be benchmarked against other dairies in a specific region. The goal is for the ratio to be close to or above 1 for production and fertility data.

For example, looking at a data set from dairies in the Southwest, the top 20 percent of herds had an average pregnancy rate of 11.75 percent during the summer and 18.08 percent during the winter, equating to SW of 0.67.

This is compared to the average of the bottom 20 percent of herds in the pregnancy rate data set. These herds had a SW of 0.22, the result of dropping from 22.07 percent in the winter months down to 4.56 percent during the summer.

Comparing the average numbers from the herd’s three worst and three best months will show the difference heat stress causes. Bilby said, “If you have a group of local peers, compare your SW ratios to theirs to see how you can improve.”

He explained that until comparing with others, many dairymen did not know how much heat stress was hurting them. “The SW ratio is a great tool to monitor the effects of seasonal changes,” Bilby noted.

Heat stress and genetics

For years, the dairy industry has been using genetic selection to increase production as well as other traits. Why not select for heat-tolerant genes then? Labs have located this gene, according to Hansen.

However, he explained, “There is a problem because there is a correlation between rectal temperature and milk production.” Not wanting to cause production to decrease, scientists are trying to find other genes that can reduce body temperatures during hot periods.

Since the major dairy breeds originated in European areas, they are not very heat-tolerant. Great heat-resistance benefits could come from crossing with breeds such as the more tolerant Gir.

However, most breeds like this have very low milk production, making even the crosses not the best economical choice. Soon it could be possible to transfer the heat-tolerance genes of the Gir into breeds like Holstein, keeping high production and gaining heat resistance.

The University of Florida has around 30 cows with the “slick gene” that can help reduce heat resistance. Experiments have been done comparing them to regular Holsteins. With the decreased amount of hair, the slick gene cows’ sweat leaves the hair follicle more easily.

In summer months, fertility greatly decreases from heat stress. This cannot be stopped with A.I. or using natural mating. However, embryo transfer has been seen to greatly increase fertility during times of heat. It has been found that most of the damage happens very early. By day 3, embryos are quite resistant, and by day 7, they are almost completely resistant to heat stress.

Embryos are transferred around day 7, bypassing the time where they are most vulnerable. Not only does embryo transfer help increase the number of offspring and genetically superior females within a herd, but it can also help to maintain fertility during heat-stress periods. PD

Rylin Lindahl is a freelance writer and a student at California Polytechnic State University in San Luis Obispo, California.