It’s not difficult to justify heat abatement for your lactating cows. The math is usually pretty easy when you look at potential returns on investment. Additional income from a 10 percent or higher increase in milk production adds up quickly.

But it isn’t quite so clear-cut in the case of pre-fresh cows. Previous research centered on shade versus no shade for these cows, and there didn’t seem to be much difference in performance, says Todd Bilby, University of

Arizona extension dairy specialist. “Plus, most research focuses on lactating cows.”

However, recent research shows that providing evaporative cooling for cows before calving pays off in improved reproductive performance during their next lactation, as well as increased milk production.

Here’s why you should consider evaporative cooling for these cows.

Physiological activity

If you think that dry cows handle heat stress better than lactating cows, think again. Cooling during the dry period, especially the late dry period, is particularly critical. That’s when a number of important physiological processes occur, including mammary gland regeneration, rapid fetal growth and colostrum production. It is also when follicles for the next reproductive cycle develop and mature.

“When dry cows are heat-stressed, it damages all follicles and the eggs inside,” explains Bilby. But, more importantly, it damages the small follicles and eggs inside which will not ovulate for 40 to 50 days later, coinciding with the start of the breeding period during lactation. Because of the damage, fertilization chances are reduced, making it unlikely the eggs will develop into viable embryos.

Heat stress during this time can also affect endocrine responses that may increase abortions and shorten gestation length. In addition, it may also decrease thyroid hormones and placental estrogen levels, while increasing blood non-esterified fatty acid concentrations.

According to researchers at TexasA&MUniversity, the metabolic heat load of the dry cow is approximately half of that of a lactating cow that produces 65 pounds of milk per day. While this heat load is low relative to a cow’s dissipation capacity, it’s thought that the endocrine system is more sensitive to even moderate heat stress during the dry period than during lactation.

Furthermore, heat stress depresses dry matter intake, which impacts post-partum milk production and a host of metabolic disorders as cows move through the transition phase.

More than shade

Cooling offers you the greatest opportunity to reduce these negative effects.

And shade does help because it reduces the solar load on the animals. Back in 1984, Florida researchers found that cows with shade during the dry period had increased blood levels of prostaglandin F metabolite, increased ovarian volume, increased diameter of the largest follicle and corpus luteum and a higher percentage of cows with a corpus luteum than cows without shade. Meanwhile, other research found no differences in services per conception, days open or days to first estrus between the two groups.

Therefore, it’s going to take more than shade to accomplish your goals. “The key is evaporative cooling,” says Bilby.

Research published in the December 2006 journal Livestock Science shows that feed-line sprinklers, fans and shades reduced services per conception and days open, while increasing milk production during the ensuing lactation.

The study found that days open for Holstein cows under evaporative cooling during the dry period decreased nearly 19 days — from 89.1 days for non-cooled cows to 70.3 for the cooled cows. And services per conception dropped from 2.49 for the non-cooled cows to 1.92 for the cooled cows.

More milk in the tank

Need more evidence that this is a worthwhile endeavor? Research published in the June 2006 Journal of Dairy Science shows that adding shades and fans to a feedbunk-mounted sprinkler system have financial rewards. The results were compared to a pen of cows that only had sprinklers. The cows in each pen were at least two weeks from calving.

The cows in pens with maximum cooling had a 60-day milk production total nearly 186 pounds above that of cows that were under sprinklers only. According to the study’s partial budget, that nets you a projected economic return of $8.92 per cow. For every 100 cows, that’s an additional $892 per year in your pocket.

The study did not show a dramatic increase in cow health, but researcher Dale Moore, Washington State University director of veterinary extension, notes that the 3,000-cow California dairy where the study was conducted was well-managed, so there was less disease incidence than other herds may experience. And, she adds, “This dairy is ahead of the game in terms of cow cooling.”

Still, Moore believes a positive effect on health and reproduction may be extrapolated from the research. During that critical dry period — as dry matter intake has a tendency to spiral downward — cooling remediated that decrease and kept feed consumption up, she says.

“In addition to a significant milk response, there is a health response in that all of those ancillary metabolic diseases are probably reduced,” Moore adds. “We were able to get cows off to a better start in all phases — production, health and reproduction.”

When you look at everything — the extra milk production and health benefits compared to the cost of fans, shade structures and water — it certainly makes a good deal of sense to use evaporative cooling for your dry cows, she says.

Bilby agrees. “We can show a financial return on investment, as well as improved animal and reproductive performance. Why not do it?”

Set cooling priorities

When investing in cow cooling, be sure to set priorities and follow them.

Your very first priority should be to ensure that all cows, including pre-fresh and lactating cows, have adequate water, says Dale Moore, Washington State University director of veterinary extension. “That means all cows can drink as much as they want, whenever they want.”

Second, provide shade for all cows, lactating and dry.

Next, add fans and sprinklers to all groups for evaporative cooling. “It is especially important to cool close-up, fresh and early-lactation cows,” she says. Then, you can move down the list to mid- and later-lactation cows and the early dry-off period.

“At a minimum, cows should have water to drink and shade. Then, get water on their backs.”