Dermatophytosis or ringworm is extremely common in dairy calves and may occur in adult cows as well. Trichophyton verrucosum is the most common pathogen, with lesser instances of Trichophyton mentagrophytes and other dermatophytes. Calves over 2 months of age through yearling stage are most commonly affected. This coincides with the ages of young dairy animals that are grouped rather than managed individually. The causative organisms are extremely hardy and survive on inanimate objects, bedding, and soil for months after cattle have been removed. Concentration or grouping of young cattle—especially during the winter months—leads to an increased incidence in herds having the problem. It is not unusual to find yearly epidemics in heifers on farms that have had ringworm in the past. Conversely, herds that do not have clinical ringworm seem to remain free of the problem unless new animals that are infected are introduced. Adult cattle may experience severe infections as well. These outbreaks tend to occur during the winter months and frequently follow infected freshening heifers being introduced into the milking herd. Although adult cows that had ringworm when calves have been assumed to be “immune for life,” the existence of outbreaks in adult cattle raise serious questions as to the longevity of immunity following natural exposure.
Dermatophytes affect the keratinized layers of skin thanks to toxins and allergens with resultant exudation, crusting, and alopecia. Fungal organisms themselves do not invade tissue and survive best when they provoke little host inflammatory reaction. Lesions tend to be oval or circular and are often multifocal. Incubation requires 1 to 4 weeks, and lesions persist for 1 to 3 months in most circumstances. Infection by contact is accelerated by mechanical irritation of the skin by contaminated objects. Stanchions, neck straps, halters, milking straps for old-fashioned bucket milking machines, brushes or curry combs, chutes, and other devices may spread infection through a group of cattle.
Chronically ill, unthrifty, poorly nourished, or acutely ill cattle will show diffuse or rapidly progressive lesions compared with herdmates. This may imply either cellular or humoral factors that contribute toward worsening of dermatophytosis. Calves persistently infected with BVDV and calves with BLAD are examples of animals that frequently have severe ringworm lesions, whereas healthy herdmates remain either unaffected or have only mild lesions. Adult cows or heifers with typical ringworm lesions may progress to diffuse lesions when stressed by acute severe infections such as pneumonia or peritonitis. Exogenous corticosteroids will worsen existing ringworm lesions.
Lack of sunlight also has been proposed as a contributing cause because animals penned indoors seem to have a higher incidence. This theory also led many veterinarians to administer vitamins A and D as a treatment.
However, the appearance of ringworm in both calves and adult cows during the summer months seems to diminish the importance of sunlight in prevention or cure.
Round or oval areas of crusting and alopecia that range from 1.0 to 5.0 cm in diameter are typical for ringworm in calves. Early lesions may appear raised because of serum oozing or secondary bacterial pyoderma underlying the crust. In calves, the periocular region, ears, muzzle, neck, and trunk are most usually affected, but lesions may occur anywhere.
Head and neck lesions are common because lock-ins, stanchions, or neck straps become contaminated and help spread the disease. Posts or beams that are used for scratching may provide an area that infects the trunk in a group of heifers. The escutcheon is another area that frequently is affected with one or more lesions. Skin lesions may be painful but are rarely pruritic.
In adult cattle, the lesions may be anywhere on the body but often appear on the trunk and neck, with fewer cows showing the typical facial lesions found in calves. In addition to oval and circular lesions, larger geographic lesions of ringworm occasionally appear in adult cattle.
During ringworm outbreaks in adult cattle, individual cows that experience unassociated systemic illness may show dramatic worsening of their ringworm lesions.
Ketotic cattle treated with corticosteroids also will show worsening of the ringworm condition. Adult cattle also may have lesions on the udder, skin of the flank, or hind limbs that increase the risk of zoonotic disease because these lesions occur where milkers come into contact with the animals. Lesions of ringworm in milkers or handlers of infected cattle are a common occurrence.
Ringworm is the most common example of a zoonosis in cattle practice.
Cultures of hair from the peripheral zone of a lesion on selective media such as dermatophyte test medium, scrapings of lesions for mineral oil or potassium hydroxide preps, or skin biopsies can be used to confirm the diagnosis, but clinical signs usually suffice. Early lesions may be sufficiently raised in appearance to mimic warts or other lesions, but careful examination will differentiate them.
The self-limiting nature of ringworm infection in most cattle that are otherwise healthy makes it difficult to assess how much, if at all, the treatment helped natural healing. Controlled studies are essential for any product to be proven as efficacious against ringworm.
Treatment often is requested because of zoonotic potential or because an affected heifer or cow has been selected to go to a show or a sale. Animals with ringworm, as with warts, are ineligible for admission to shows or sales. This latter situation often leads to the sudden “emergency” status of ringworm even though it has been present on the animals for months.
Before discussing various treatments, one must realize the magnitude of the labor required to treat hundreds of ringworm lesions in a group of calves, heifers, or cows.
The failure of treatment and lack of owner interest in it are simply based on the sometimes impossible task of catching, restraining, and treating groups of heifers.
Treatment more often involves selected animals that need to be “cured” so they can enter a fair or a show.
Owners who are willing to treat their calves also should be educated about disinfection and prevention.
Topical treatments that probably are efficacious are:
Numbers 1 through 3 are applied as a spray or dip daily for 5 days, then once weekly until cured.
Topical treatments that may be effective for limited lesions or selective treatment of a few animals:
Systemic treatment that probably is efficacious:
Systemic treatments that may be efficacious:
Brushes, curry combs, and clippers used on infected animals should be cleaned and disinfected.
Workers handling the cattle should wear gloves or wash thoroughly following handling of the animals with an iodophor or tincture of green soap.
Disinfection of premises and fomites offers the best opportunity to avoid future outbreaks. Physical cleansing and pressure spraying can be followed with lime sulfur or Clorox disinfection. Premises should be allowed to dry and supplied with new bedding. Only animals without detectable lesions should be reintroduced.
Vaccines have been developed in some parts of the world and have been reported to be efficacious.
The normal blood calcium concentration in adult cows is between 8.5 and 10 mg/dl, which translates into a total plasma pool of only about 3 g in a 600-kg individual. It is evident that to meet the calcium needs of colostrums production, fetal maturation, and incipient lactation at the end of gestation (collectively these requirements may reach 30 g/day), adult cows will need to mobilize substantial amounts of calcium from bone and increase the efficiency of gastrointestinal tract absorption.
Mastitis is very common in dairy farm, it results in great economic losses
Dermatophilosis, also called Streptothricosis or rain scald, is a common skin infection of cattle and other large animals caused by Dermatophilus congolensis. Moist environmental conditions and long hair coats predispose to contagious infection by D. congolensis.
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