Use Nutrition to Help Combat Heat Stress
The calendar may say March, but it’s time to get your summer nutrition plan in place. If you wait for heat stress to occur and then decide to take action to minimize the negative effects of heat stress, you are already behind. Abrupt ration changes can cause problems of their own.
The goal, says Bob Collier, professor of animal sciences at the University of Arizona, is to formulate an action plan for nutrition before heat stress starts. The plan should be specific. For example, when the temperature-humidity index (THI) hits this number, we do this. Or when feed refusals increase above x we do this. Work with your nutritionist to develop a list of nutritional management strategies to combat heat stress that is tailored to your dairy.
These nutrition strategies should be used in conjunction with a cooling program that is also tailored to the conditions at your dairy. Shades, fans, soakers and nutrition all play an important role in minimizing heat stress for dairy cows. While cooling alone makes a difference, when combined with proven nutritional strategies, the results can be even better.
Heat stress causes more than just a drop in dry matter intake (DMI) and lost milk production. Cows lose a lot of potassium from sweating and panting. Thermal stress has been shown to increase potassium requirements by as much as 12%, explains Collier. Research also has shown that heat stress increases the buffering requirements of the rumen, and it suppresses immune function.
It also causes changes in cow behavior. Cows drink more water, eat less during the day, often don’t display estrus and they seek out shade. When it is hot, “cows instinctively want to stay in the shade,” says Collier. “They will move with the shade structure’s shadow, and they will choose to stand in the shade even when fans and soakers are running at the bunk.”
Cows perceive that the shade is cooler. Heat-stressed cows also will choose to lie in the alley in wet manure instead of the stalls. The increased exposure to manure combined with a suppressed immune system leads to more cases of mastitis during heat stress.
But if you can control the cows’ behavior, you can reduce the incidence of disease and minimize heat stress. For example, in a north-south oriented barn, afternoon sun forces the cows to seek shade away from the feedline where the fans and soakers run. Installing a curtain on the west side of the barn to block the afternoon sun provides shade and encourages cows to eat feed and rest in their stalls. Having a curtain allows you to take full advantage of the soakers and fans at the feedline. Otherwise, when the sun hits, the cows leave to seek shade.
Cooling cows is a top priority. Shades, fans and soakers all play an important role in combating heat stress. So too does nutrition.
The first step is to talk with your nutritionist about implementing a summer ration. A summer ration may, for example, include higher quality forages with higher rates of digestibility to help reduce the total heat load created from digestion. Lower quality forages take more time to digest in the rumen and therefore generate more heat.
Another summer ration strategy is to increase the nutrient density of the diet by adding concentrate or fat to the diet. Supplements such as buffers, ionophores, yeast and additional potassium also can be helpful. What you choose should be tailored to your dairy. It should be based on available feeds, cost, milk price and room in the diet, explains Collier. Cows should be acclimated to the summer ration before heat stress begins. Then, if additional nutritional changes are needed to help cows’ maintain DMI, the changes will be smaller and less stressful to the cows’ digestive system.
Lactating cows are the cows most in need of a summer ration. Dry cows and close-up cows should already be on a diet tailored to their needs. However cooling dry and close-up cows is tremendously important. (Please see "It Pays to Cool Dry Cows" in this issue.)
Check water availability. Cows need 2 to 3 linear inches of waterer space. Tanks should be shaded and clean with ample water pressure to keep up with demand during warm weather – especially exit lane waterers.
Once heat stress begins, pay close attention to feed refusals by pen. When feed refusals increase, it’s time to alter feeding management. Feed more of the ration at night, and push up often to encourage intake. If DMI cannot be maintained by feeding during the cooler hours of the day, nutrient density can be recalculated. Remember, the cow’s nutrient requirement does not change during heat stress; changes in feeding management and nutrient density can help cows meet their needs.
You’ll also want to track the incidence of acidosis. If you see an increase in acidosis, adding more buffers to the diet can help.
It’s also a good idea to track the temperature-humidity index at your dairy. THI quantifies the severity of heat stress. Cows experience heat stress when the THI rises above 68. Anytime the THI hits 80 during the day, death losses may increase – especially in sick cow pens. Even with proper cooling and nutritional strategies in place, when the THI climbs above 85, severe heat stress and losses can occur.
Sick cows and high-producing cows are the most susceptible to heat stress. They are already stressed by illness or by high milk production, and heat stress can tip the balance to disease or death. Many herds don’t cool sick cow barns, says Collier. But this is where heat stress can quickly lead to increased death loss.
There is a lot we can do to minimize heat stress. Cooling, combined with nutritional management strategies, can make a big difference to limit losses and keep cows healthy and productive. Talk to your nutritionist today to develop your nutrition action plan for heat stress.