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s 4he case of the cu­ri­ous coat pat­tern s 5neven sweat­ing s )mmune de­fi­cien­cies eX­plained

Q: My horse Leo de­vel­ops an un­usual coat pat­tern over his whole body ev­ery sum­mer. The length and tex­ture of the hairs are all about the same, but the hairs grow in dif­fer­ent di­rec­tions. His win­ter coat ap­pears to be nor­mal, and af­ter he sheds out, I don’t re­ally no­tice the pat­tern un­til the end of June. Once it reap­pears, the pat­tern is fairly sim­i­lar each year, although it does change a bit.

Leo is 13 now, and his coat has done this ev­ery year since I got him when he was 8. He is healthy and sound, with no prior in­juries that we know of. He is not itchy, and he has no le­sions, no sen­si­tiv­i­ties to in­sects, no hives. My ve­teri­nar­ian has never seen this coat pat­tern, but she found no prob­lems when she ex­am­ined him about a month ago, and she did not seem alarmed. What might be caus­ing this? Is it any­thing to worry about?

Karin Bombeli

Red­mond, Wash­ing­ton

A: Your horse ap­pears to have whorls---patches of hair that lie in the wrong di­rec­tion. These are not un­usual, although your horse’s case is ex­treme. These odd whorls and vary­ing di­rec­tions of hair growth do pop up from time to time--I have seen one other horse with odd

whorls to this ex­tent. In some cul­tures these sorts of pat­terns are care­fully noted and serve as the ba­sis for in­di­vid­ual horse iden­ti­fi­ca­tion.

Chances are, the pat­tern is there year-round, but maybe it’s less no­tice­able in his win­ter coat---the longer hairs may be more inclined to lie as they are brushed de­spite the un­der­ly­ing whorls. As long as he is healthy, this is per­fectly nor­mal---for him. D. Phillip Spo­nen­berg, DVM, PhD,

ACT (Hon­orary) Vir­ginia–Mary­land Col­lege of

Vet­eri­nary Medicine Blacks­burg, Vir­ginia

A: I re­call see­ing a horse with a sim­i­lar bizarre pat­tern about 15 years ago, but with­out fol­low-up.

The ques­tion of “Is it any­thing to worry about” is prob­a­bly de­pen­dent on the age of the horse. This horse is on the young side for a di­ag­no­sis of PPID (pi­tu­itary pars in­ter­me­dia dys­func­tion, also called Cush­ing’s dis­ease), but this dis­ease has been di­ag­nosed in horses as young as 7 years old.

This case would be the an­tithe­sis of a horse with PPID---which is typ­i­cally char­ac­ter­ized by a long hair coat that does not shed out. But it might be worth run­ning a di­ag­nos­tic test any­way just to rule it out. The rea­son I say this is that I know of a don­key that be­came al­most to­tally hair­less (also the an­tithe­sis of PPID) but grew its hair back af­ter it was started on per­golide.

If you wanted to pur­sue fur­ther tests, it might be in­ter­est­ing to take skin biop­sies from both the af­fected and un­af­fected ar­eas, although I am not cer­tain this would lead us to a di­ag­no­sis. Stephen D. White, DVM, DACVD Univer­sity of California–Davis Davis, California

HAIRY SIT­U­A­TION: These pho­tos, taken in spring, sum­mer and win­ter, show the un­usual coat pat­tern that Leo de­vel­ops each year. The 13-year-old geld­ing is healthy and sound and has no known al­ler­gies or past in­juries.

LOOK­ING FOR CLUES: Leo’s owner de­scribes the area in ques­tion as be­ing sim­i­lar to other parts of the coat but “the hairs grow in dif­fer­ent di­rec­tions.”

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