Sub-acute rumen acidosis slowly damages the health of your cows, which can cause a decrease in dry matter intake and milk production.

Think ahead to the Thanksgiving dinner that you'll be eating in a few weeks: It provides a useful comparison to acidosis problems in your cows. First, you probably won't eat a balanced diet. Second, you'll probably over-eat at dinner and then skip supper. And, finally, you may suffer from indigestion.

In cows, those same factors can lead to rumen acidosis. The primary culprit is eating an unbalanced, low-fiber diet - a common occurrence in finicky, just-fresh cows.

However, while big meals, such as Thanksgiving, may be infrequent for you, the cows on your farm must fight off acidosis on a continuous basis. In fact, low-lying cases of the disease, called sub-acute rumen acidosis or SARA, may be affecting nearly 20 percent of your fresh cows. With symptoms that are difficult to detect, this disease can nag at your cows' health, causing a decrease in dry matter intake and loss of milk production.

Symptoms hard to see
According to Gary Oetzel, veterinarian at the University of Wisconsin's School of Veterinary Medicine, cows experience SARA when the rumen pH registers between 5.5 and 5 on a pH scale of one to 14, with seven being neutral. Clinical acidosis begins when the pH drops below 5.
But, detecting SARA through visual observation of cows is much tougher. Often times, SARA eludes producers and veterinarians because cows show few symptoms, and those that do surface are difficult to link to sub-acute rumen acidosis.

For example, cows can go off feed for short periods of time until the rumen corrects itself and pH rises - similar to a person not wanting to eat when he has indigestion.

Oetzel estimates that a bout of rumen acidosis causes a cow's dry matter intake to temporarily drop by 5 percent to 10 percent, or between 2.5 to 5 pounds for the average cow consuming 50 pounds of dry matter per day. In a pen of 100 cows with 20 percent experiencing SARA, the feed refusal due to the disease would be 50 to 100 pounds - or just 1 percent to 2 percent - at any given time.

The occurrence of lameness, specifically sole ulcers and abscesses, also can indicate SARA. But lameness also can be caused by poor stall design and excessive time standing on concrete. It takes a second look to determine if acidosis is the reason for the foot problems on your farm.

High production "walks the line"
Some producers may consider a low-level occurrence of SARA a necessary side effect of feeding cows for high milk production. Research based on obtaining rumen fluids from cannulated cows suggests the ideal rumen pH is slightly acidic or between 6.3 and 6.5. "When optimizing rations for milk production, you walk right up to the line of acidosis," says Oetzel.

However, the advantage gained from higher milk production can diminish when the rumen dips below 6.3 on the pH scale, says Mary Beth Hall, dairy nutritionist at the University of Florida. "Once you get below 6.2, you have a noticeable depression in fiber digestibility," she says, and that, in turn, deters milk production.

Even with a good ration, what keeps the cows and your milk production on the right side of the line is your management, says Hall. On one dairy, problems with bunk management or slug feeding can result in SARA, while the same ration fed down the road at a different dairy results in high milk production and no acidosis problems.

Overproduction of acid harmful
The problems from SARA compound when a cow consumes rapidly-digesti-ble carbohydrates, causing its rumen to cut production of volatile fatty acids and increase production of lactic acid. This encourages the growth of other harmful microbes and bacteria in the rumen, and can affect a cow's health in three ways:

1. Rumenitis. Low rumen pH causes damage to the papillae, an event called rumenitis. The papillae aid digestion by absorbing volatile fatty acids. During short bouts of SARA, the papillae can recover. But, continued assaults can cause permanent damage. Researchers have begun implanting rumen pH probes into the rumen to track the duration of SARA and clinical acidosis. The chart above shows the results of a Canadian trial which monitored transition cows.

2. Liver abscesses. When excess acids are produced in the rumen, the damage to the rumen lining allows harmful bugs, including bacteria, to enter the blood stream and infect other parts of the body. Liver abscesses can result, contributing to poor animal performance. While little is known about the occurrence of liver abscesses in dairy cattle, they occur at a rate of 15 percent to 25 percent in beef cattle raised in feedlots. Acidosis is a wide-spread problem in beef cattle feedlots due to the high amount of grain fed to achieve rapid gains, and dairy nutrition experts suspect lactating dairy cows are affected at a similar rate.

3. Damage to lungs and blood vessels. The circulatory system can spread harmful organisms and toxins leaking from the rumen to other sites in the cow's body. First, bacteria can reach the lungs, resulting in pneumonia. Second, these bacteria can invade tiny blood vessels in the lungs, causing them to burst. One sign of this, often seen by producers, is sporadic nose bleeding in affected cows. Lameness in cows also has been linked to damage of the blood vessels in the feet caused by toxins produced from rumen acidosis. The capillaries carrying oxygen and nutrients to the feet constrict and expand at a faster rate, causing swelling, tissue damage, and pain in the sensitive lamina in the feet.

Subclinical problems may prove difficult to quantify or discover, but consequences of poor health - namely decreased dry matter intake and lost milk production - commonly associated with SARA, demand your attention.

Is your herd free of subclinical acidosis? Take this quiz.

Answer the following questions about your feeding and management program to see how well you do at preventing acidosis in your herd.

Any question that you answer "no" to indicates an area or symptom of SARA that you need to examine. Work with your veterinarian, nutritionist or consultant to optimize your feeding program.

1. When using a Penn State particle separator box on your total mixed ration, do you consistently find about 7 percent to 12 percent of the particles on the top screen (which would be greater than 1.5 inches in length)?

2. When walking through the barn, do you consistently see at least 50 percent of the cows not eating, sleeping or chewing their cuds?

3. When your veterinarian conducts rumenocentesis on a portion of your just-fresh and peak-intake cows, do the results indicate that fewer than 25 percent of the cows tested have a ruminal pH of less than 5.5? (Remember, rumenocentesis results tend to run 0.2 to 0.4 points below the rumen pH from research samples collected through a rumen cannula.)

4. When feeding diets high in starch (those with large amounts of corn and barley), do you keep the non-structural carbohydrate level within 35 percent to 40 percent of the ration's dry matter?

5. If you do not have a TMR mixer, is hay the first feedstuff that you deliver in the morning?

6. Does the dry matter intake of your animals remain consistent - with no more than a 2 percent day-to-day variation from the group's monthly average?

7. When looking at individual cow records, do you see many cows with a milk protein percentage that is more than 0.4 percentage point greater than the milk fat percentage?

8. When feeding low-starch diets with hay-crop silage and byproducts, such as cottonseed hulls and corn gluten feeds, do you keep the non-structural carbohydrate level within 40 to 45 percent of the ration's dry matter?

9. Does your forage neutral detergent fiber remain above 20 percent?

10. Three weeks before calving, do you begin to feed cows grain to get the "starch digester" microbes in the rumen working and increase the length of rumen papillae that absorb volatile fatty acids?

11. After placing a buffer in the ration at the level recommended for the group's milk production, do you find cows consuming less than 0.5 pounds per cow per day of a free-choice buffer that you also offer?

12. Do new cases of sole ulcers and sole abscesses occur at a rate of less than 10 percent per year in your entire herd?

Does your feeding schedule result in the cows' feeding area never being empty?

In your component-fed herd, do you start feeding fresh cows 8 to 10 pounds of dry-grain concentrate, increasing that amount by 2 to 3 pounds per week to reach peak feed at 6 to 8 weeks after calving?

When analyzing your cows' manure, do you rarely find watery manure or manure containing whole corn kernels or cottonseeds?