Dermatophilosis (rainrot) is a common skin condition in cattle caused by the Dermatophilus congolensis bacterium. It is most often seen in cattle living in areas with a wet, mild climate or in dry regions which develop a large amount of seasonal moisture.

D. congolensis is able to infect multiple animal species, many can act as reservoirs. It is maintained in environments by living within chronic skin lesions of carrier animals, which become reactivated with excessive exposure to moisture. In order to infect cattle, there needs to be a skin break or irritation, such as that caused by:

• External parasites (lice, mites)
• Irritating insects (flies, midges, mosquitoes)
• Morning dew exposure
• Penetrating thorns or awns
• Abrasions, lesions or wounds
• Excessive rubbing of skin against objects

What it looks like
Papules initially develop on the cow's body or face, which turn into pustules. The hairs become matted together and form thick crusts, which can easily be removed in clumps. The underlying skin is reddened, scabby, with mild erosions or evidence of proliferation and exudate.