Farming Magazine - October, 2012

COLUMNS

Dairy Nutrition: Summer Heat and Laminitis

By John S. Hibma

As I write this article near the end of July, summer is still alive and well, hot and humid. By the time the cooler weather of fall comes along, we all tend to forget about how hot the summer was. Often, though, on many dairies, cases of laminitis are more numerous in the fall. Both the weather and nutrition during the hottest days of summer are the cause of foot problems that appear in the fall.

A lot of dairy farmers who see laminitis starting to flare up in late summer and early fall are unsure what's causing it. Was it something in the feed? Could it be that green and/or half-cooked corn silage you're feeding right now? Probably not. More than likely the foot problems were set in motion when nutrition got all goofed up while cows were struggling to stay cool during the blistering heat wave a couple of months earlier.

Dairy cows really get clobbered when the heat and humidity are high. The optimum temperature for cows to remain comfortable is between 25 and 70 degrees Fahrenheit. As temperatures reach 75 degrees Fahrenheit at a relative humidity of 64 percent or reach 80 degrees Fahrenheit at a relative humidity of 30 percent the cow begins to respond negatively to the environmental heat load. Under mild heat stress, cows begin to cool themselves by sweating and rapid breathing. Cattle only sweat 1 percent as much as humans, so increased breathing rate all the way to open-mouthed rapid panting becomes the main response for cows trying to keep cool. Under optimum conditions the respiration rate of cows is around 65 breaths per minute. As cows approach mild heat stress their breathing rate increases above 70 breaths per minute. Respiratory rates above 80 breaths per minute are indicative of a serious heat load in cows. All of this discomfort will prevent a cow from eating the way she should.

Especially in herds in which forages and concentrates are fed separately, the consumption of forages tends to decline more rapidly and to a greater extent than the intake of concentrate feeds. This greatly upsets the pH balance in the rumen. Cows tend to eat fewer meals of which concentrates make up a larger percentage, setting the stage for an acidotic rumen. The combination of energy-dense rations that are high in starch and intermittent feeding patterns increases the risk for acidosis and, consequently, laminitis.

Remember back to those oppressively hot days during the summer when cows were standing or lying and panting like an old steam locomotive? They weren't eating the way they should and rumens were not getting all the effective fiber they should. The short explanation is that the rumen pH dropped, which sets up a progression of problems that ultimately affect blood flow down by the foot. The resulting laminitis is an inflammation of the tissue just above where the hoof material is formed. The way these parts are connected make them more vulnerable to blood and fluid buildup. The greater the level of inflammation, the more pronounced the laminitis is and the more damage it can do to the foot if left untreated.

The amount of time a cow has to stand on concrete will also have an impact on how severe a case of laminitis is. Having to stand around all day on a sore foot only makes the problem worse. Making sure freestalls and bedding are properly managed so a cow has a place to lie down when she needs to will also help alleviate foot problems. Confinement on hard surfaces will contribute to a mechanical form of laminitis just because an already sensitive foot is experiencing more


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There are two major nutritional components related to laminitis and lameness: the feed ration and the management of feeding cows. While making sure that feed rations are properly balanced for your cows all year long is necessary for both milk production and overall health, monitoring the diet during a heat wave is even more critical due to the increased chances that rumen health can be compromised. Make sure that effective fiber is consumed and the cows don't have an opportunity to sort the feed. Bunk management becomes an important factor as well. Make sure feed is fresh and palatable during the heat. Adjust feeding schedules so cows can spend more time at the feed bunk during the coolest parts of the day or night. Also make sure there is ample water available at all times.

Increase the rumen buffers during the summer months to reduce the chances of rumen acidosis. Even though cows only sweat a fraction of what humans do, they do stand to lose minerals when they sweat. Keeping potassium and magnesium levels at higher levels will help maintain adequate electrolyte levels. The addition of zinc-methionine and biotin to dairy diets has also shown improvements in hoof health.

Heat stress can occur at a variety of heat and humidity combinations. Excessively high levels of relative humidity along with high temperatures make for the most dangerous combinations. In regions of the country where humidity tends to be low, cows can tolerate fairly high temperatures. As the humidity level rises, a cow's tolerance to higher temperatures declines. Fans and evaporative cooling systems can help to moderate an oppressive housing or milking environment.

To a large degree, the prevention of laminitis is really a management issue. You can't prevent the heat, but you can create an environment that decreases the stressful effects of heat. I'm going to go out on a limb here and ask the (mostly) obvious question, "Why don't dairy farmers set up or retrofit their barns so that it never gets more than 70 degrees Fahrenheit and the relative humidity can be kept below 65 percent?" All you need are some fans and some misters. I realize that money doesn't grow on trees, but speaking from experience, cooling systems are one of the least costly renovations you can make to a dairy facility and it only takes one hot summer to get your money back out of the investment. In these days of increasingly narrowing profit margins, preventing the long-term damage caused by laminitis will help keep cows healthy and productive.

The author is a dairy nutritional consultant and works for Central Connecticut Farmer's Cooperative in Manchester, Conn.