Jan, 2, 1920.] Agricultural Gazette of N.S.W, 43 



Trefoil Dermatitis* 



CHAS. L. O'GORMAN, M.R.C.V.S,, Government Veterinary Officer. 



This disease, although known in certain parts of New South Wales for a 

 considerable number of years, may not be recognised by many farmers under 

 the above name. It is manifested by an eruption of the skin, the parts 

 suffering being those that are devoid of pigment. Horses are generally affected 

 about the lips, nostrils, coronet or pasterns when these situations have 

 white or pink markings ; cattle are also afiected about the lips, and any other 

 parts where the coat is white. In sheep the lips, nostrils, face and ears are 

 the common sites of the disease ; and in shorn sheep the back and flanks 

 become affected. 



In slight cases there may be only redness, itching, swelling, and subsequent 

 desquamation of the epidermis on the white portions of the skin. In more 

 extreme cases, however, the skin, which is at first red, becomes swollen 

 and covered with vesicles and pustules, which burst and discharge. In 

 such cases the affected parts often become covered with crusts or scabs of 

 dried exudate and blood, and very commonly — as a result of the animal 

 biting, scratching, or rubbing the affected parts — large raw, excoriated sur- 

 faces are produced which may suppurate, or dry and become cracked and 

 fissured. Necrosis and sloughing may follow as a result of infection of these 

 wounds, and the loss of an ear is not an uncommon occurrence in sheep. 



Of Dietetic Origin. 



In the absence of any definite knowledge as to its true nature, this disease 

 was generally known as "aphis disease," the aphis being regarded as the 

 cause, notwithstanding the fact that aphides were never found on the 

 lesions. 



Light was thrown on the subject by the investigations cai'ried out by Dr. 

 Dodd, D.V.Sc, F.R.C.V.S., a report by whom was published in 1916, which 

 proved conclusively that the disease was not due to aphides, but was dietetic 

 in origin, being caused by feeding mainly or exclusively upon the common 

 trefoil {Medicago denticulata). It was found that feeding on trefoil rendered 

 the skin very sensitive to the sun's rays ; and when exposed to continual 

 direct sunshine an erythematous dermatitis was produced on the pink or 

 white portions of the skin, i.e., on the unpigmented parts. Even in the 

 unpigmented areas lesions do not occur if such areas are protected from the 

 dii'ect rays of the sun. 



Three factors were found to be necessary for the production of this 

 disease: — (1) The food must consist entirely or mainly of trefoil; (2) the 

 animal must possess unpigmented skin ; (3) such unpigmented skin must be 

 exposed to the direct action of the sun's rays. 



