GE­NET­ICS Go­ing gray

EQUUS - - Eq Consultant­s -

Q:In my 70 years, I have seen many a gray horse, both dap­pled or flea-bit­ten, turn to­tally “white” with age. But now I have two---a 21-year-old Quar­ter Horse and an 18-year-old Quar­ter Horse-draft mix---who over the last few years have been be­com­ing more and more fleabit­ten. Even the one that was dap­pled is now go­ing flea-bit­ten. Could this be due to a di­etary is­sue? Mary Lewis Cal­li­coon Cen­ter, New York

A:Gray horses are caused by an in­ter­est­ing gene. The gene is dom­i­nant and can ap­pear in com­bi­na­tion with any other coat color or pat­tern. At first, the gene seems to in­crease pig­men­ta­tion, so that many young gray horses are quite dark. Over time, the pig­ment cells be­gin to de­crease, and the horse grad­u­ally whitens. Some gray horses go through a nicely dap­pled stage; oth­ers less so.

How­ever, in some horses the gray gene seems prone to re­vert to the orig­i­nal form, so that some ar­eas of the coat re­gain the abil­ity to pro­duce pig­ment. This is what hap­pens in the flea-bit­ten ar­eas---these are small spots where the D. Phillip Spo­nen­berg, DVM, PhD, is a pro­fes­sor of pathol­ogy and ge­net­ics at Vir­ginia–Mary­land Re­gional Col­lege of Vet­eri­nary Medicine. He is the au­thor of Equine Color Ge­net­ics, and his ar­eas of re­search in­clude ge­net­ics of do­mes­ti­cated an­i­mals, coat color hered­ity, con­ser­va­tion of rare live­stock breeds, di­ag­nos­tic pathol­ogy and re­pro­duc­tive pathol­ogy.

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