Summertime is great for eating ice cream, but the heat and humidity can be dangerous for dairy cows, lowering milk production and threatening their health, says Dr. Meggan Hain, staff veterinarian at Penn Vet’s Marshak Dairy at the New Bolton Center.

Most modern dairy cows start to experience mild heat stress at a heat index (a combination of heat and humidity) of about 68ºF. By the time the heat index reaches 80ºF, most cows will feel significant heat stress if they are not offered some form of relief.

This heat stress can cause a loss in appetite, which can lead to a drop in milk production of up to 10 pounds of milk per day. It can also suppress the immune system, leading to increased susceptibility to common diseases and increased severity of those diseases. Finally, heat can have more subtle effects, such as long-standing reproductive suppression and a decrease in total lactation production.

Because of their big rumens, cows are very susceptible to heat stress. The good microflora in the rumen that break down cellulose also produce a significant amount of heat, so it’s like having a furnace inside all year round.

The more milk a cow is making, the more she is eating and the more susceptible she is to heat stress. Also the large size of some breeds, like black-and-white Holsteins, makes it more difficult for them to radiate heat.

Hain offers these 10 tips to help beat the heat and to alleviate heat stress in dairy cattle:

1. Plenty of water

During cooler weather (40°F), a 1,500-pound dairy cow producing 80 pounds of milk per day will drink an average of 25 gallons of water per day. The same cow will drink 33 gallons of water a day in hot weather (80°F). Cows that are producing more milk will need even more water. There must be at least 3 inches per cow in the pen of space along the water trough; this will decrease competition and ensure that all animals have access to clean water.

2. Shade

Studies have shown a 10 to 20 percent increase in milk production for cows offered shade in pasture versus those without access to shade. For high-producing, lactating cows, this is essential, but don’t forget the heifers and dry cows out on pasture and those sick or down cows that are less able to move out of sunny areas.

3. Fans

Fans will help remove radiant heat. Choose fans that are 36 to 48 inches wide, and place them 8 feet off the ground, 20 feet apart, at an angle of 15 to 25 degrees downward toward the ground to offer continual airflow. Fans can be spaced across the barn to create good airflow in all areas.

4. Sprinklers

Sprinklers over the feed alley, combined with fans, provide the best heat removal in most commercial barns by using evaporation to help cool the cows. The sprinklers should be placed at 8 feet off the ground, just under the fans, with a 180-degree spray and a 10-psi water flow, directed over the cows’ backs. A good sequence is to have the sprinklers on for about three minutes out of 15 minutes. This soaks the cows and then allows the fans ample time to evaporate the water and cool the animals. Soakers over the beds should be avoided as it causes increased moisture, which can contribute to environmental mastitis.

5. Misters

In some drier climates, farms are able to use misters attached to fan systems over the beds to provide evaporative cooling of the air in the barn. The misters provide a fine spray that is designed to evaporate before settling on the beds. This evaporation will cool the air slightly. These systems work well in low humidity and high airflow environments, but should not be used in high humidity or closed environments, as they can increase the heat index.

6. Dietary changes

Decreasing concentrates and supplementing fats can increase the energy density of the diet while decreasing the heat produced by fermentation. Do not increase the fats above 6.5 percent of dry matter. Decreasing the forage content or feeding higher quality forages will also reduce the heat from fermentation. On hot days, cows will prefer concentrate, but adequate roughage should be fed to avoid digestive upset. There are also minerals such as potassium (1 percent of dry matter) and chromium, which can help with heat tolerance.

7. Focus on fresh cows

During the summer months, the fresh cows will be more susceptible to metritis, mastitis, ketosis and other diseases because the cows will eat less during this critical period and their immune function will decrease. By monitoring the fresh cows closely, you can diagnose these problems earlier and address them more aggressively before they become critical. With added heat stress, 12 hours can make the difference between a sick cow and a dead cow.

8. Focus on the holding pen and milking parlor

One of the hottest places on the dairy farm is the holding pen, due to the high density of the cows, which does not allow them enough space to radiate heat. Cows need a minimum of 36 to 48 square feet to prevent heat transfer between cows. When moving cows up to the holding pen, bring up smaller groups instead of a whole pen. This will mean that the cows are waiting for a shorter time before entering the milking parlor and will prevent packing too tightly. The holding pen also needs fans and sprinklers to alleviate the heat stress in this high-risk area. Giving the cows access to water soon after exiting the milking parlor can also help encourage water intake and prevent milk drop during the summer.

9. Don’t add to the stress

Don’t work cattle (moving, sorting or transporting) or give vaccinations on very hot days. Anything that adds to the stress of the cattle – vaccinations certainly add stress to the immune system – can make the difference between a cow that can cope with her heat stress and a cow that is pushed over the edge into illness. This includes dry cows that could abort their calves due to excessive stress.

10. Tunnel ventilation with cooling cells

The most effective model for smaller farms is to use a combination of cooling cells and tunnel ventilation. This combination can decrease the temperature in the barn by up to 10 degrees from the outside temperature. While this is one of the most effective ways of cooling a dairy barn, it is not feasible for a large-scale facility. PD

—From Penn Vet news release