Greys and Melanomas

[graciespook]

#ed_op#DIV#ed_cl##ed_op#FONT face="Arial Black"#ed_cl#I found this on EMG..very very interesting..we can thank TrueColours for this article. #ed_op#/FONT#ed_cl##ed_op#/DIV#ed_cl##ed_op#DIV#ed_cl##ed_op#FONT size=1#ed_cl##ed_op#/FONT#ed_cl# #ed_op#/DIV#ed_cl##ed_op#DIV#ed_cl##ed_op#FONT size=1#ed_cl##ed_op#/FONT#ed_cl# #ed_op#/DIV#ed_cl##ed_op#DIV#ed_cl##ed_op#FONT size=1#ed_cl##ed_op#/FONT#ed_cl# #ed_op#/DIV#ed_cl##ed_op#DIV#ed_cl##ed_op#FONT size=1#ed_cl#quote:#ed_op#/FONT#ed_cl# #ed_op#/DIV#ed_cl##ed_op#DIV#ed_cl##ed_op#HR#ed_cl##ed_op#/DIV#ed_cl##ed_op#DIV#ed_cl##ed_op#BR#ed_cl#Thought I would post this paper on grey horse syndrome - I have been sitting on it for over 2 years, waiting for a couple of University genetics departments to evaluate it. If I am right, it has some fairly wide implications, #ed_op#BR#ed_cl#Cheers #ed_op#BR#ed_cl#Kerry Morgan #ed_op#BR#ed_cl#PS Spelling is Autralian BTW, not incorrect - we spell "colour" and "grey" like this. #ed_op#/DIV#ed_cl##ed_op#P#ed_cl#Grey Horse Syndrome #ed_op#P#ed_cl#By Kerry Morgan B.A.Dip.Ed - October 24, 2003 #ed_op#P#ed_cl#(Revised Nov 2, 2005) #ed_op#P#ed_cl#Tesio was correct - grey in horses is not a "colour" or a "factor" - it is a "disease of the coat". #ed_op#P#ed_cl#Does any other animal go grey like a horse goes grey? There are animals that are grey in colour but they are born grey, there are shades of grey and agouti among cats, dogs, rabbits, goats, there are “blue” cows, there are even other colours in the horse that appear grey, such as blue roan, and roan associated with Appaloosa colouring. People lose their hair colour from middle to advanced age. But unique among animals, horses “go grey”. #ed_op#P#ed_cl#A grey horse is can be born any colour, and the greying of the coat begins some time after birth and progresses. Very aged grey horses are white, with or without a “fleabitten” effect. Breeders can usually identify a foal that will turn grey by the presence of grey hairs around the eyes. Only foals that have at least one grey parent can go grey, but conversely a foal with 2 grey parents may remain non-grey, even in breeds with a high percentage of homozygous greys such as the Lippizanner. #ed_op#P#ed_cl#A grey horse has the usual complement of genes for colour and/or pattern inherited from both parents, but geneticists have long regarded the tendency to “grey out” as a factor that acts in addition to the genotype for coat colour. The inheritance pattern for grey follows Mendelian rules. It can be homozygous or heterozygous, and it is dominant in that if the animal carries one gene for the factor, the horse will appear grey. A grey horse must have at least one grey parent, ie the factor cannot be carried recessively. #ed_op#P#ed_cl#I believe that the “factor” that makes a horse go grey is in fact an inheritable dominant mutation which affects the skin and hair of the grey horse, and which in its full expression is “grey horse melanoma”. #ed_op#P#ed_cl#Gower (1999, p. 60) states the following: #ed_op#P#ed_cl#Throughout the life of a grey, pigment is removed from the hair and redeposited in the gut or skin, and this is thought to be responsible for…the slow-growing deposits of pigment loosely termed ‘melanoma’. #ed_op#P#ed_cl#Fintl & Dixon (2001) refer to a 1972 survey by Stannard which indicated that “more than 80% of grey horses over 15 years old were affected with such [melanotic] growths”. #ed_op#P#ed_cl#In the same article, Yager et al (1993) is quoted as suggesting that all grey horses would eventually develop such lesions if they lived long enough. #ed_op#P#ed_cl#Drs Sutton and Coleman from Uni. Qld. studied 97 grey horses and 16 coloured horses at a pet food abattoir, and “found that all grey horses aged greater than [an estimated] 15 years had evidence of melanoma lesions.” Also, they stated that though a number of horses showed no signs of lesions before death, tumours were found post-mortem. They concluded that “all grey horses of either sex are likely to develop melanotic tumours given time.” (Sutton & Coleman, 1997). #ed_op#P#ed_cl#Melanoma in grey horses has been known for centuries. Often the presence of small, slow-growing tumours does not affect the usefulness or general health of a grey horse, but in other cases the tumours are larger, more numerous, they progress more rapidly and they interfere with the horse’s comfort or well-being. Tumours often present initially on the dock or around the anus, and sometimes they affect the parotid region where they can interfere with the jugular, the windpipe, or the movement of the jaw when eating. #ed_op#P#ed_cl#Various treatments have been used with limited success, such as surgical excision, cryotherapy, chemotherapy and immunotherapy (Fintl et al 2001). Treatment with cimetidine and other H2 antagonists (Goetz and Long, 1993) was regarded as “beneficial in the management of melanomas in some horses.” #ed_op#P#ed_cl#A question that occurs is, do solid-coloured horses ever develop so-called ‘grey-horse melanoma’? They certainly develop other types of cancer, but is this particular type of equine cancer only found in greys? #ed_op#P#ed_cl#It is amazing that all the evidence has been right in front of horse breeders for centuries, but it seems no-one has looked critically at the process of greying in the horse for what it is - a pathology. #ed_op#P#ed_cl#Perhaps we are seeing more of these grey horse melanomas because horses used for recreational purposes are working into their twenties, or are being kept as retired companions where once they would have been put down when their useful years were over. #ed_op#P#ed_cl#What are the implications for grey horses? Should you buy a grey? #ed_op#P#ed_cl#Research suggests that although all grey horses will eventually show symptoms of melanoma, in a percentage of cases it will have no significant effect on their health or ability to be worked. #ed_op#P#ed_cl#Many greys do not exhibit symptoms of the disease until they are quite aged . (Foley et al (1991) suggest that “melanomas in young horses…appear to show more variation in location and also in coat colour of affected animals.”) Some grey horses are asymptomatic into advanced old age, though tumours may be found post-mortem. #ed_op#P#ed_cl#Depending on the size, location and nature of the tumours, even a horse with melanoma can live for many years after showing symptoms. The tumours are usually “benign”, though in some cases they may metastasise (Yager et al 1993). #ed_op#P#ed_cl#Unless tumours interfere with other organs, they do not appear to cause the animal pain. #ed_op#P#ed_cl#In conclusion, rather than grey horses being “prone” to equine melanoma, it is more accurate to say that a syndrome exists which in its early expression changes the coat colour to grey. #ed_op#P#ed_cl#In some individuals the disease then progresses and primary tumours develop usually on the dock or around the anogenital area. #ed_op#P#ed_cl#In a further percentage of grey horses the tumours become more widespread and/or occur around the head and neck. #ed_op#P#ed_cl#In cases where tumours of the parotid region occur and restrict eating or breathing, or in cases where anogenital tumours complicate elimination, the animal may have to be euthanised. #ed_op#P#ed_cl#Basically, if you purchase a grey horse, there is a probability that at some stage in its life it will develop some symptoms of melanoma. It would be possible to eradicate grey horse melanoma by eliminating greys from all breeding programs, but this would be unrealistic, particularly since in a large percentage of cases the syndrome has no ill effect on the animal - there is evidence to suggest that in some populations, individuals seem more resistant to the development of tumours. #ed_op#P#ed_cl#Owners of grey horses should however be aware that grey horse melanoma is the result of a genetic mutation rather than a “disease” in the normally understood sense of the term, and that as such there are unlikely to be effective “cures” developed. #ed_op#P#ed_cl#References #ed_op#P#ed_cl#FINTL, C & DIXON, P.M. (2001) A review of five cases of parotid melanoma in the horse, In: Equine Veterinary Education 13 (1) 17 - 24 #ed_op#P#ed_cl#FOLEY, G.L., VALENTINE, B.A. & KINCAID, A.L. (1991) Congenital and acquired melanocytomas (benign melanomas) in eighteen young horses. Vet. Path. 28, 363 - 369 #ed_op#P#ed_cl#GOETZ, T.E. & LONG, M.T. (1993) Treatment of Melanomas of Horses. Comp. Cont. Educ. Pract. Vet 4, 608 - 610 #ed_op#P#ed_cl#GOWER, J (1999) Horse Colour Explained, Simon & Schuster (Australia) Pty Ltd, Sydney (pp 55 - 60). #ed_op#P#ed_cl#SUTTON, R.H. & COLEMAN, G.T. (1997) Melanoma and the Greying Horse, In: RIRDC Research Paper Series No 97/55 RIRDC Project No. UQ-28 University of Queensland #ed_op#P#ed_cl#YAGER, J.A, SCOTT, D.W. & WIL****, B.P. (1993) The skin and appendages, In: Pathology of Domestic Animals, Eds: K.V.F. Jubb, P.C. Kennedy and N. Palmer, Academic Press Inc., San Diego, pp 719 -721#ed_op#/P#ed_cl##ed_op#DIV#ed_cl##ed_op#/DIV#ed_cl#