Non-infectious Bovine Diseases/Disorders
Description and Cause
A common condition that often necessitates the use of antibiotics in cattle is "footrot" or what is medically termed interdigital phlegmon. It is an infection of the soft tissue between the claws (digits) of the feet and is caused by two anaerobic bacteria (these are bacteria that grow in the absence of oxygen ), Fusobacterium necrophorum and Bacteroides melaninogenicus. These bacteria are common in the environment and F. necrophorum is present in the rumen and feces of normal cattle. Once these bacteria invade the skin of the foot, they rapidly cause the condition we recognize as footrot. Injury or damage to the skin between the claws allows this invasion to occur. Common factors that can cause damage of this sort include:
· Stubble fields,
· Small rocks and pebbles,
· Abrasive surfaces.
Additionally, high temperatures and excess moisture or humidity causes the skin between the claws to chap and crack allowing these bacteria to invade. With wet winters and springs, the advent of hot weather provides the ideal conditions for footrot to become a major problem in the summer.
The appearance of footrot is fairly typical and begins as a swelling of the skin between the claws. This swelling usually begins within 24 hours of the onset of the infection. The toes become separated due to the swelling and the skin appears reddened. The foot is very painful and the animal can be quite lame at this time. A fissure or crack develops along the swollen area for part or all of the length of the interdigital space. Yellow to grayish tissue extends from this crack and the lesion has a characteristic foul odor. The area around the coronary band can be swollen and red. Affected cattle can have a mild fever, refuse feed, lose weight, and be mildly to severely lame. Also, it is common for affected cattle to lose a considerable amount of weight during a bout with footrot. If the footrot lesion does not heal satisfactorily, very serious problems can develop. The structures just beneath the skin of the foot include the bones of the foot, the tendons, and joint of the foot. If these underlying structures are invaded by bacteria-particularly the joints, bones, or tendons, therapy is very difficult and the chances of recovery are much lower.
Footrot can usually be recognized in typical cases; however, a number of conditions can be confused with footrot. These conditions include:
· Puncture wounds due to nails,
· Needles, or other sharp objects,
· Sole abscesses,
· Fractures of the bones of the foot,
and a newly recognized condition that primarily affects dairy cattle, "Hairy footwarts".
All lame feet should be carefully examined and it should not be assumed that all lame cattle have footrot. If you have any questions regarding the condition affecting your cattle, you should contact your veterinarian for diagnosis and advice.
Treatment of footrot is relatively straightforward and if instituted early in the course of the disease is usually successful. For mild cases, local treatment can be accomplished by thoroughly cleaning the foot, applying an astringent (such as 5% copper sulfate), and then applying an antibacterial dressing. For moderate or severe cases, systemic antibiotic therapy is usually recommended. All label directions should be carefully followed including withdrawal times before slaughter. If a dose higher than that listed on the label is used, the antibiotic is being used in an extra-label manner and a veterinarian's prescription is needed and an extended withdrawal time determined by your veterinarian must be observed. If deeper structures of the foot become infected, consult your veterinarian.
The most important preventative measures are to insure that damage to the feet of cattle is minimized. Other preventive measures include footbaths, feeding of organic iodine, feeding of zinc methionine, and/or vaccines. Footbaths can be used to prevent cases; however, they are not particularly useful in the face of an outbreak. The most common solutions used are 2% formalin, and 5% copper sulfate. The two compounds must be used with caution from both animal health and environmental aspects. The formalin solution is very caustic and will damage your skin or eyes if splashed or spilled. The copper sulfate can be fatal to cattle if they drink it and must be disposed of carefully to avoid damaging aquatic plants and animals. Footbaths should be used 3 to 4 times per week to be effective and should not be used for long periods of time (greater than 3 weeks). The cattle should have clean feet before entering the foot baths (pre-washing may be necessary) and only 300 head can be done before the solution should be changed. Using formalin footbaths too frequently (daily for 4-5 days) can cause irreversible damage to the cattle's feet.
There are also commercial vaccines that have limited effectiveness in preventing footrot in cattle; it is important to strategically time the administration of these vaccines so that maximum protection is achieved during the time of year when cattle are at the most risk. Your veterinarian will also know of local factors that may be of importance in preventing footrot, so be sure to discuss this matter with him/her before spending a lot of time, money or effort on control and prevention measures. Since footrot is an infectious disease it is important that your cattle's immunity is not abnormal and thus a good feeding and supplementation program is necessary. The key to managing footrot is prevention, because treating a large number of individual animals can take a lot of the fun out of summer.
By John Maas, DVM, MS
Coccidiosis causes significant economic losses in cattle. Although most cattle are exposed to coccidia and infected, most of the infections are self-limiting and mild or asymptomatic. The parasites that cause this condition are members of the species Eimeria, and the most important of this species for causing disease in cattle are Eimeria bovis and Eimeria zuernii.
The life cycle of these parasites is complex. Single cell oocysts are passed in the feces of cattle, are resistant to disinfectants, and can remain in the environment (particularly moist, shady areas) for long periods of time and maintain their infectivity. The oocysts sporulate and these sporulated oocysts are ingested by the host and the sporozoites are released in the intestine. Sporozoites enter the intestinal cells, form trophozoites, which in turn divide into many merozoites. These merozoites penetrate additional intestinal epithelial cells and form more meronts. Eventually, macrogametes and microgametes are formed which combine to produce the next generation of oocysts. When the oocysts are mature, they rupture the host cell and are released into the lumen of the intestine and pass out in the feces. The reproduction of these organisms is phenomenal as illustrated by the following:
1 oocyst X 8 sporozoites
X 120,000 first generation merozoites
X 30 second generation merozoites
X 80% macrogametocytes
= 23,040,000 oocysts
Cause and Severity of the Disease
The potential damage to the intestinal cells is obvious. It is estimated that as few as 50,000 infective oocysts ingested by a young susceptible calf can cause severe disease. The replication of the coccidia within the host's intestinal cells and the subsequent rupture of the cells is responsible for the disease and the clinical signs that develop.
The severity of the disease is directly related to the dose of infective oocysts that are ingested. The more oocysts ingested, the more severe the subsequent disease. With light infections, the damage to the gut cells is minimal and because the cells in the gastrointestinal tract are replaced rapidly the damage is quickly repaired. In the case of heavy infections, about two weeks after the oocysts are ingested, most of the epithelial cells at the base of the intestinal glands are occupied by meronts or gametocytes. As these cells rupture, damage is severe and there is loss of blood into the feces. Also, fluid, electrolytes, and blood proteins (albumin) are lost.
Most animals infected with coccidia do not show signs of illness. This is due to the normally low dose and after a course of infection the animal is immune to that particular Eimeria species. However, this does not mean they are immune to all Eimeria species. Therefore, coccidiosis is primarily a disease of the young where there is crowding, stress, and/or nonimmune animals. Older cows certainly act as a reservoir and shed oocysts into the environment. Stress such as shipping, weaning, dietary changes, steroid therapy, and other problems can precipitate an outbreak of coccidiosis. Older cattle immune to their own endemic species of coccidia can become infected and/or ill when moved to a new herd and exposed to a different species.
The clinical signs of coccidiosis can include the following:
· Diarrhea (bloody at times)
· Straining (tenesmus)
· Loss of appetite
· Fever (slight)
Death (in severe cases)
Many cattle are affected and experience weight loss or decreased weight gains without showing obvious illness and these cattle account for the majority of the economic losses. Your veterinarian can diagnose coccidiosis on the basis of clinical signs, fecal oocysts examinations, and post mortem examination of dead animals (if that occurs). By John Maas, DVM, MS