animal care and health

By Mary Beth De Ondarza
The author has a dairy nutrition consulting business, Paradox Nutrition, LLC, in Plattsburgh, N.Y.

Claw disorders generally are related to a combination of rumen acidosis issues and problems that result in too much weight being handled by parts of the hoof. Infections, such as warts, foot rot, heal erosion, and interdigital dermatitis, affect the foot skin. Foot baths can help to prevent infections but not claw disorders.

Laminitis is an inflammation of the sensitive tissues (lamellae) of the hoof. It is caused by damage to the blood vessels that supply oxygen to the lamellae. The primary cause of laminitis is the absorption of large amounts of lactic acid across the rumen wall to the blood, producing systemic acidosis. Systemic acidosis reduces the ability of the blood to carry oxygen. The feet of the cow, being the furthest distance from the source of oxygen at the lungs and being supplied by very tiny blood vessels, suffer the most from the reduction in the oxygen-carrying capacity of the blood.

With the lack of adequate oxygen, fluid leaks out of the blood vessels in the lamellae causing swelling, pressure, and pain. Since the lamellae are located in between the outside wall of the hoof and the coffin bone (on the inside), some people have compared this pain to that of wearing a tight, uncomfortable pair of shoes. However, rather than having pain in specific spots, the cow has pain over most of her hoof.

What to watch for . . .
Signs of subclinical laminitis:
• Cows "plod" as they walk or look like they are "walking on eggs" but are not obviously lame.
• Cattle often stand with feet close together or crossed.
•There is pinkness or puffiness of the coronary band.
• Cows will rock back and forth on their feet and appear restless.
• The texture of the horn softens and is vulnerable to infection, wear, and damage.
•Visible hemorrhages of the sole may appear as pink striations.
• First-calf heifers during the first 30 to 90 days in milk are most susceptible. Signs of clinical laminitis:
• Noticeable hoof wall changes occur over time.
• There's increased claw horn growth often shifting weight-bearing surfaces.
• Hooves widen, flatten, and develop ridges. This condition also is called "slipper foot."

Subclinical rumen acidosis occurs when the pH of the cow's rumen drops below 5.8. Rumen microbes ferment starches and sugars to form volatile fatty acids (VFA), with propionate being a significant end product. Excessive accumulation of propionate in the rumen reduces pH and encourages the growth of lactate-producing microbes. Abrupt surges in grain intake also result in more lactate production. As lactate is a stronger acid than propionate, its accumulation in the rumen further reduces pH, further raising the risk of rumen acidosis.

It generally is recommended that high-production rations contain 21 to 27 percent starch and 4 to 6 percent sugar. At the same level of total dietary starch and sugar, however, one ration containing a large amount of sugars and fast-fermenting starches such as barley, high-moisture corn, or bakery product may result in acidosis, whereas a ration containing a more slowly degradable starch like cornmeal may not. Heat and pressure make starches more rapidly fermentable. For high energetic efficiency, high starch availability is desirable, but a combination of rapidly and slowly available starches will help to control acidosis. Typically, I like to limit rapidly degradable starch sources to not more than 60 percent of the total starch in the ration.

Feeding management and cow comfort will, in part, determine how much starch and sugar can be fed. If a total mixed ration (TMR) is fed, rather than feeding components of the ration individually, you can include higher levels of starch and sugar in the ration. Without TMR feeding, you should feed grain as many times per day as possible (at least four times a day). Avoidance of slug-feeding grain (no more than 10 pounds fed at one time) is important. If the ration is consistent on a daily basis, more rapidly fermentable starch and sugar can be tolerated in the ration.

Watch for sorting . . .
Cows can ruin a TMR by wiggling their noses as they push through their feed to sort out the grain portion of the TMR before consuming the forage at a later time. Many factors affect TMR sorting. It is important that you obtain a uniform mix to start with. Cows will tend to sort out long, coarse hay or straw particles if they exceed 2 to 3 inches in length. Adding water to the TMR to obtain a ration moisture level of around 43 percent can reduce sorting. It also helps to feed more times per day and have at least 5 percent refusals.

Ideally, the TMR in front of the cows for all 24 hours of the day should look like the TMR that came out of the mixer wagon.

Without adequate effective fiber and saliva production, the risk of rumen acidosis shoots up. Cows need to ruminate about 8 hours per day and eat for between 4 and 5 hours. Thus, at least 50 to 60 percent of the cows should be ruminating when observed 3 to 4 hours after fresh feed has been fed.

It generally is recommended that 15 percent of the particles in the diet should exceed 1.5 inches in length. Roughage should ideally be fed before grain or in a TMR. This will help to create the rumen mat and stimulate rumination at a time when acid production is high.

More than acidosis . . .
According to University of Florida researchers, 90 percent of lameness occurs in the rear foot, and 70 to 90 percent of that involves the outside claw. Since acidosis problems would affect the oxygen circulation of all claws equally, these statistics strongly suggest that laminitis involves much more than simply acidosis problems.

Your cow-handling practices and cow comfort also impact the incidence on laminitis. Many times I have seen laminitis issues in cows that were consuming fairly healthy diets. I particularly remember one herd that had a 15-inch high stall curb (as opposed to the recommended 10-inch curb). Cows were not using the stalls and not lying down as much as they should.

Pasture is forgiving on cows' feet while concrete is not. When we put cows on concrete, their soles get flatter. The outside claws of the back feet bear the most weight and thus, have the most problems. Just like we get callouses on our feet in places that bear more weight, the cow grows more hoof horn on her outside claw due to excessive weight bearing. She then starts to rotate her feet outward to try to get more comfortable. At this point, she is set up to become lame when she experiences a bout of acidosis. The goal of hoof trimming is to correct these weight-bearing imbalances before problems occur.

Calving time is critical. It is out of our control that certain enzymes and hormones produced at calving time weaken the collagen fibers of the cow's hoof. Early-lactation cows also often have inconsistent intakes, making them more susceptible to rumen acidosis. For these reasons, it is especially critical to not have cows standing any more than they need to during the three weeks before and after calving. The feet of transition cows will suffer the most from heat stress, overcrowding, long periods in the lock-ups at the feed bunk, and too much time in the holding area before milking.

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