PG . 38
HORSE HEALTH
ARTICLE BY : DR JOHN KOHNKE - BVSc RDA
RAIN
SCALD in Horses ...
Rain scald , also known as mycotic dermatitis , rain rot or mud fever , is a common skin condition which is favoured by wet weather . The common cause is a fungal-like organism ( Dermatophilus congolensis ) which colonises the skin of horses , cattle and sheep .
Horses which share pastures with
sheep or cattle often have a higher risk of rain scald or even ‘ greasy heel ’, which is also caused by the same organism , combined with skin reaction to sunlight on non-pigmented skin ( horses with white socks on their hind fetlocks and pasterns ).
Although it is a soil contaminate , it is difficult to culture the fungal-like organism from soil in muddy areas . Studies have shown that the common black house fly ( Musca domestica ), which are often prevalent in large numbers after rain as they breed in manure , can spread the organism as they swarm around and transfer it to horses via their legs and feeding proboscis .
There are various forms of rain scald , ranging from ‘ cinder ’ or ‘ sand ’ burn on the front of the hind limbs of working horses , to greasy heel and generalised infection in foals kept in muddy conditions .
Horses with areas of nonpigmented skin are highly susceptible when they have a solar UV sensitivity and are grazing wet pastures . The infected areas feel warmer to the touch and are often matted and painful in severe infections .
WET CONDITIONS FAVOUR RAIN SCALD The rain scald organism is a common inhabitant on the skin of horses , but under ideal wet and warm conditions , it will invade the skin . The skin on the flat parts of the body of the head , withers , topline and rump are more likely to be affected as water from rain cannot drain away as quickly to dry the skin .
Light , misty rain favours the fungal colonisation on the head and legs , especially on horses grazing on long grass which keeps wetting and can abrade the skin .
After a period of wet overcast weather , horses kept outdoors are more likely to develop severe form of rain scald along the top-line and rump . Often staphylococcus ( staph ) bacteria create a secondary infection to increase the degree of irritation especially if the horse rolls on contaminated dust or mud in a yard , resulting in skin inflammation and oozing exudates , which can mat the hair over infected areas .
YOUNG , AGED AND NEW HORSES ARE MOST VULNERABLE Horses which have been challenged or partly infected often develop some degree of immunity to invasion by the organism . However , horses turned out from dry stables into wet weather and highly contaminated soil and pasture are more likely to develop rain scald within a few days .
Young and aged horses with poor skin immunity or newly introduced horses from a property with low contamination are also likely to develop and suffer from acute or chronic rain scald , as well as greasy heel .
DIAGNOSIS OF RAIN SCALD Diagnosis is based on the typical lesions with loss of hair in tufts , heat and swelling , leaving a ‘ juicy ’ or pus-filled crater , or small hard , sensitive and itchy lumps under the saddle and tack . This is often caused by the secondary invasion with staph species bacteria harboured on the skin . The skin can be swabbed and then the samples
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