My horse used to be external alot and she used to roll around within the mud very soon it looks approaching her fur is plucking?
To fix this problem the scabs should be removed while bathing the horse day by day for seven days with either iodine shampoo, chlorohexidine shampoo or benzoyl peroxide. Severe cases may require treatment with antibiotics for a week or two. Warm sun and dry weather are nature's best cure for rainfall rot. Skin problems should be addressed early in the disease since the itching, hair loss and subsequent inflammation become severe enough to result in oozing, crusting and scale of the skin.
It could also be Ringworm. Ringworm is a fungal infection that spreads from horse to horse through common grooming tools, saddle pads or harness. Generally, damp, crowded and poorly lit conditions (winter and fall) will predispose a horse to ringworm.
Ringworm is often seen in childlike horses (one to three years old) or older, debilitated animals. Initially, ringworm lesions will appear as small, circular patch of hair loss with scabby or flaking skin beneath. If untreated, these lesions may progress to colossal, asymmetric areas of broken hairs and blister formation with scabs. Ringworm lesions are typically found over the girth and saddle areas, obverse (around eyes) and legs. Occasionally, ringworm lesions are very itchy. Ringworm is extremely contagious both horse to horse and horse to human. If you suspect ringworm, begin treatment without beating about the bush. This includes isolating the affected horse and disinfecting all tack and grooming equipment.
To fix this try Clorox bleach (diluted in ratio of 1:10 within water) and a medicated shampoo (miconazole). Treatments should be repeated daily for five days, then weekly until lesions are heal.
Hope your horse feels better!