Dairy farmers don’t think twice about fine-tuning rations or investing in a milking system performance review if changes to these systems offer a way to improve milk production and quality. Shouldn’t the same consideration be given to heat abatement strategies? After all, heat stress robs dairy farmers of $900 million every year in reduced fertility, lost milk production and other health challenges.

Research and practical experience show that estrous expression, follicle quality, pregnancy and conception rates, as well as embryo quality, all drop dramatically in summer months while embryo losses increase. For example, dairy cows are 3.7 times more likely to lose their embryo during hot versus cool seasons.

Another study found undetected estrous events estimated at 76 to 82 percent on a Florida dairy for the months of June through September. That percentage dipped down to 44 to 65 percent for the months of October through May.

Furthermore, today’s hard-working dairy cow feels the effects of heat stress at lower temperatures than you might think. Previous studies and the temperature-humidity index used for years noted that cows usually began to feel heat stress at 72ºF.

However, the latest research suggests that a temperature humidity index reading of 68ºF is a more accurate point to begin cooling cows.


It is factors like these that suggest that preventative actions taken today can go a long way toward mitigating the costly effects of heat stress tomorrow. That’s because the consequences often linger long after temperatures cool, explains Dr. Todd Bilby, Texas AgriLife Extension dairy specialist.

“There are many ways to help maintain reproductive performance when temperatures rise this summer,” he says. “The key is to find the combination of actions that work best on individual farms.”

With that in mind, now’s the time to think about a heat stress checkup and determine where actions can most effectively counteract its effects on a herd’s reproduction – long before temperatures, and the battle, heat up.

1. Cooling remains the key component of any heat abatement strategy.

• First, check system maintenance. How did soakers, nozzles and fans fare during the off-season? Clean fan blades and nozzles, and replace all system components that are damaged or broken.

• Next evaluate whether enough cooling is in place. “Assess where any ‘hot’ spots may still exist for the cows,” suggests Dr. Bilby. “How warm do they get and where do the spikes occur? We have the tools to track cow temperatures so you can identify problem areas.” For instance, holding areas remain a cooling opportunity on many farms.

• Assess how long cows spend in this and other problem areas. If a farm hasn’t yet invested in cooling these areas, wherever they may be, it may be time to expand the cooling system.

• Make sure all cows have access to plenty of clean, fresh water, as consumption during periods of heat stress can double their normal intake. Add waterers to exit lanes if they haven’t already been installed and add regular waterer cleanout and maintenance to employee to-do lists.

2. Consider alternatives to heat detection. “Adopt a correct, robust, timed artificial insemination (A.I.) protocol with no heat detection for the summer months,” says Dr. Bilby.

“Most people don’t think about making the change just during the summer months but, since accurate heat detection can be more difficult during hot weather, it can be a good option. Then go back to heat detection within your timed A.I. program during cooler weather if it fits with your breeding protocol.”

Research at the University of Florida observed an increase in the number of cows pregnant at 90 days postpartum or 120 days postpartum in a timed A.I. protocol versus cows inseminated at first observed estrus.

3. Use A.I. for more breedings. It’s not unusual for dairies to breed cows to A.I. sires for the first several cycles, then move cows into a bull pen if they have not conceived. However, heat stress can compromise bull fertility, which negatively affects reproductive performance.

Heat stress decreases sperm concentration and motility and increases the percentage of abnormal sperm in an ejaculate. Interestingly, semen quality does not return to normal for up to two months following periods of heat stress.

“Instead of moving cows into a bull pen after three breedings, consider using A.I. another time or two to offset negative effects of heat stress on bulls and increase the odds of getting a pregnancy,” recommends Bilby. Also, invest in a breeding soundness exam for any bulls used on your farm. This is a good idea regardless of season.

4. Other factors are impacted, too.

• If you practice visual heat detection during the summer (or any time for that matter), make sure heat detection is accurate. Brush up on primary and secondary signs of estrus and offer training on these signs to key employees. Also consider combining a couple forms of heat detection to help better identify which cows to breed – like adding tail chalking to visual observation.

• Embryo transfer has been shown to increase fertility during summer’s heat. Studies at Texas A&M AgriLife Research and Extension found that conception rate nearly doubled (from 20 percent to 39 percent) when cows received fresh embryos versus conventional A.I. The conception rate for cows implanted with frozen embryos was similar to that of conventional A.I.

“There are some challenges with implementing this strategy,” Bilby notes. “However, embryo transfer can significantly enhance fertility during the summer.”

• Supplemental hormone therapy with either GnRH or hCG at and/or after A.I. has also been studied as a means to enhance embryo survival, progesterone concentrations and increase fertility. “Timing is a challenge and data from this research are marginal,” says Dr. Bilby.

“Some studies show improvement and others show no improvement, so at the end of the day, it may be something to consider, but it’s not something I can necessarily recommend at this point.”

Ultimately, improved cooling is still the most profitable and effective way to improve both reproduction and milk production during the summer months, Bilby concludes. “Reproductive programs can be modified through breeding protocol modifications, embryo transfer and continued A.I. to bypass critical time points during which heat stress appears to be the most detrimental to animal performance."

"Consider implementing an aggressive reproductive program during the summer to help counter the effects of heat stress and improve cows’ reproductive performance.” PD

Click here to email an editor for references which have been omitted due to space.

—Excerpts from February 2012 Dairy Cattle Reproduction Council newsletter

Ultimately, improved cooling is still the most profitable and effective way to improve both reproduction and milk production during the summer months. Photo by PD staff.