Summer heat and humidity may be great for corn, but is dangerous for dairy cows. Heat stress can drop milk production and threatening cow health, warns Dr. Meggan Hain, staff veterinarian at Penn Vet's Marshak Dairy at New Bolton Center.
Most dairy cows start experiencing mild heat stress at a heat index (a combination of heat and humidity) of about 68 degrees. Once that index hits 80 degrees, most cows will feel significant heat stress if not offered some form of relief.
The larger the cow, the more difficult it is for her to radiate built-up body heat. The more milk she's making, the more she's eating, and the more susceptible she is to heat stress.
That can spell a drop in milk production of up to 10 pounds of milk per day, increase susceptibility to common diseases and have more subtle effects – long-standing reproductive suppression and a decrease in total lactation production. That's why it pays to keep her cool, says Hain.
Consider these 10 tips to help to reduce your herd's risk of heat stress:
1. Plenty of water: At 80 degrees Fahrenheit, a 1,500-pound dairy cow producing 80 pounds of milk per day will drink an average of 33 gallons of water per day – almost a third more than on a cool day. Cows producing even 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 ample access.
2. Shade: Cows offered pasture shade will produce 10% to 20% more milk than cows 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 cows less able to move out of the sun.
3. Fans: Fans help remove radiant body heat. Choose models 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 air flow. Fans can be spaced across the barn to create good airflow in all areas.
4. Sprinklers: Positioned over the feed alley and combined with fans, they provide the best heat removal in most commercial barns. The evaporation helps cool the cows. Sprinklers should be spaced at 8 feet off the ground, just under the fans, with a 180-degree spray pattern and a 10 PSI water flow, directed over the cows' backs.
A good sequence is to have the sprinklers on for about 3 minutes out of 15 minutes. This soaks the cows, 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 shouldn't 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% of dry matter.
Decreasing the forage content or feeding higher quality forages also reduces heat generated by rumen fermentation. On hot days, cows will prefer concentrate, but adequate roughage should be fed to avoid digestive upset. Minerals such as potassium (1% of dry matter) and chromium can improve heat tolerance.
7. Focus on fresh cows: During summer months, fresh cows will be more susceptible to metritis, mastitis, ketosis. As they eat less during this critical period, their immune functions decrease. By monitoring them closely, you can diagnose these problems earlier and address them more aggressively before they become critical. With heat stress, just 12 hours can make the difference between a sick cow and a dead cow.