by: Stephen B. Blezinger
Ph.D., PAS
There are few problems that are as miserable as foot pain. Having endured some minor problems with my feet over the years I can attest that foot pain will certainly shut you down. The same goes for cattle. Who hasn't looked out across their herd from time to time only to witness one animal or another limping to some degree? These situations are not unique to any part of the country and there are no singular causes. Additionally, it's almost impossible to estimate the countless dollars lost annually by cattle producers in terms of labor, medicine cost, performance and even animal loss. This article will review this problem and discuss methods to prevent and treat the condition. Aside from simple injuries to the animal's foot or hoof, foot rot tends to be the largest primary problem although these can be other related conditions that have similar symptoms. Approximately 20 percent of all diagnosed lameness in cattle is actually foot rot.
Economically in stocker cattle, weight gain is significantly reduced when grazing cattle contract the disease. In one multi-year study, Brazle (1993) reported that affected steers gained 2.3 lbs. per day, while steers not affected gained 2.76 lbs. per day. Foot rot is usually sporatic in occurrence, but the disease incidence has been reported as high as 25 percent in high-intensity beef or dairy production units.
Foot rot is a subacute or acute necrotic (decaying) infectious disease of cattle, causing swelling and lameness in one or more feet. The disease can become chronic, with a poorer likelihood of recovery if treatment is delayed, resulting in deeper structures of the toe becoming affected. Causes of foot rot can vary. Normally, an injury of some type, mechanical or otherwise occurs or there is a softening and thinning of the interdigital (between the toes) skin by continuous exposure to wet conditions (common in Spring and late Fall). These situations typically the cause of entrance points for infectious agents. A common bacteria known as Fusobacterium necrophorum is the organism most often isolated from infected feet, but can also be found in non-diseased, interdigital skin. The majority of F. necrophorum isolated belong to one of two types (types A or B) which produce toxins that cause necrosis (death) or decay of the infected tissues.
Regardless of the source once loss of skin integrity occurs, bacteria gain entrance into subcutaneous tissues and begin rapid multiplication and production of toxins that stimulate further continued bacterial multiplication and penetration of infection into the deeper structures of the foot.
Spread of the Disease
Feet infected with F. necrophorum serve as the primary source of infection for other cattle by contaminating the environment. Researchers and veterinarians disagree on the length of time F. necrophorum can survive off of the animal, but estimates range from one to ten months. This means that the condition can crop up again in a given area even after no cattle or no observed cases appear for a period of time.
Signs, Symptoms Related Problems
While this foot disease occurs in all ages and classes of cattle, increased incidence is noted during wet, humid conditions. When case incidence increases in hot and dry conditions, attention must be directed to areas where cattle gather, which are often crowded and may be wet from urine and feces deposited in shaded areas.
The first signs, following a growth and development period of the organism for a period of five to seven days, are lameness, acute swelling of interdigital tissues, and swelling evenly distributed around the hairline of both hooves. Eventually the interdigital skin cracks open, revealing a foul-smelling, necrotic, core-like material. Untreated, the swelling may progress up the foot to the fetlock or higher. More importantly, the swelling may invade the deeper structures of the foot such as the navicular bone, coffin joint, coffin bone, and tendons.
A potential problem is that there are other conditions that can cause lameness in cattle and can be mistaken for foot rot and would require different treatment. These include: interdigital dermatitis, sole ulcers, sole abscesses, sole abrasions, infected corns, fractures, septic arthritis, and inflammation or infection of tendons and tendon sheaths, all of which generally only involve one claw of the foot and not the areas of skin or soft tissues between the toes or claws.
Another common foot condition, digital dermatitis (hairy heel warts) is often confused with foot rot because of foot swelling and severity of lameness. Digital dermatitis affects only the skin, beginning in the area of the heel bulbs and progressing up to the area of the dewclaws; whereas, foot rot lesions occur in the interdigital area and invade the subcutaneous tissues. Cattle grazing endophyte infected fescue pastures that develop fescue toxicity, causing loss of blood circulation to the feet and subsequent lameness, are sometimes mistaken as having foot rot.
Treatment of the Problem
Treatment of foot rot is usually successful, especially when caught and started early in the disease course. Treatment should always begin with cleaning and examining the foot to establish that lameness is actually due to foot rot and not one of the other conditions discussed. At this point, a topical treatment should be applied. Some very mild cases will respond to topical therapy only but most cases require the use of systemic (injectable) antimicrobial/antibiotic therapy. There a number of antibiotic products on the market that can be useful. Please consult your veterinarian for his recommendation. Since many of these now require a prescription he can provide this as well.
If at all possible, affected animals should be kept in dry areas until healed. If improvement is not evident within three to four days, it may mean the infection has invaded the deeper tissues. Infections that do not respond to initial treatments need to be re-evaluated by your veterinarian sooner rather than later. He or she will want to determine if re-cleaning, removing all infected tissue, application of a topical antimicrobial, and bandaging are appropriate, along with a different antibiotic. In the more severe cases, management of the animal will be between salvaging for slaughter (following drug withdrawal times), claw amputation, or in particularly valuable breeding animals, claw-salvaging surgical procedures.
Nothing Beats Prevention
Preventive measures are focused on the prevention of mechanical damage to the foot as caused by frozen or dried mud, shredded weeds or brush (resulting in stubble), and minimizing the time cattle must spend standing in wet areas. Other preventive measures presently used include the use of footbaths (most often used in confinement dairy operations, 10% Zinc Sulfate – 16 lbs per 20 gallons of water or 10% Copper Sulfate – 16 lbs. per 20 gallons of water). Footbaths are not very practical in range cattle situations and are normally used primarily in dairies. Other preventative measures include:
• feeding low levels of chlortetracycline.
• addition of organic and inorganic zinc and organic iodine to the feed or mineral mixes.
• injection with trace mineral solutions such as MultiMin® (prescription required).
Low level feeding of chlortetracycline (CTC) is labeled through the Food and Drug Administration for beef cattle, for the reduction of liver abscesses at 70 mg per head per day. As discussed aboveF. necrophorum is the major infective agent in liver abscesses and foot rot in cattle. CTC is labeled at 350 mg per head per day (at least 0.5 mg per lb. per day) in beef cattle under 700 lbs., and 0.5 mg per lb. per day in cattle over 700 lbs., for the prevention of anaplasmosis. Consequently, many mineral mixes and commercial supplements are formulated to provide 350 mg per head per day, to control those diseases listed on the CTC label. Since foot rot is caused by the same organism as liver abscesses, some control of foot rot should occur at the 350 mg per head per day level.
Supplemental zinc may reduce the incidence of foot rot. Improvements have been seen in foot health even when zinc is not deficient in the diet when organic sources are included and overall zinc concentrations in supplements are increased. Zinc is important in maintaining skin and hoof integrity; therefore, adequate dietary zinc should be provided to help minimize foot rot and other types of lameness. In one three-year study, zinc methionine added to a free-choice mineral supplement reduced the incidence of foot rot and improved daily weight gain in steers grazing early summer pasture (Table 1).
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Feeding of organic sources of iodine have been shown to also be effective in this type of a system. Iodine from EDDI (ethylene diamine dihydriodide), an organic source, is believed to be effective in preventing foot rot although it should not be routinely fed at elevated levels year-round. Studies have reported that organic I fed at a rate of 10 to 15 mg per head per day was helpful in the control of foot rot on some farms.
Evidence has indicated that the use of injectable trace mineral solutions such as Multimin®, which contains significant levels of organic zinc as well as manganese, selenium and copper, has been shown to effectively increase zinc status in the animal and subsequent reductions in the incidence of foot rot has been observed.
Conclusions
Foot rot is one of many conditions of the foot that cause lameness in cattle. For treatment to be effective it must be started early in the course of the disease. It is normally necessary to have a break in skin integrity for foot rot to occur. The most important preventive measures are centered on the protection of interdigital skin health. All this said, however, solid preventative measures can dramatically reduce the expense of a foot rot outbreak and in general may be the most cost-effective method available to the cattleman.
Dr. Steve Blezinger is nutritional and management consultant with an office in Sulphur Springs, Texas. He can be reached at 667 CR 4711 Sulphur Springs, TX 75482, by phone at (903) 352-3475 or by e-mail at sblez@verizon.net. For more information please visit www.facebook.com/reveillelivestockconcepts.
http://cattletoday.com/archive/2013/August/CT2970.php
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