Mushroom  -  a Recently Recognised Dilution
 

The genetic cause of the mushroom colour has been found by Dr Rebecca Bellone & Jocelyn Tanaka at U.C. Davis, California. They have now developed the long awaited DNA test for mushroom so breeders have the opportunity to find out whether their ponies may carry this gene.

Further details can be found at: http://www.vgl.ucdavis.edu/services/horse/MushroomDilution.php
 

left - right: Barclay Arms Wilma (page 2), Kellas Trinket (page 3), Kellas Chiffon (page 3), April Girl of Clonyard (page 2)
 

There are several ponies registered in past UK Shetland Pony Stud-Book Society volumes that may have been mushroom. In the first volume a mare, Berghita 101, foaled in 1885, was registered as "Brown with silver points". In 1893, a filly, Unornia II, was born to a black mare, Guddonia II 1226 & the stallion, Triptolemus 45, bay with black points. Unornia was registered as "Brown, whitish mane & tail". She retained this colouring when registered as a mare (reg. no.1313) in 1898. More recently, the Avening Stud had several foals described as "dun" from chestnut parents. Avening Festina (born 1951) was "silver, flaxen mane & tail" from chestnut parents. Ponies from other studs have been registered as "cream" with two chestnut parents.

Many of the present mushroom coloured ponies have now been DNA tested to find out if they might be genetically silver but have proved to be negative for this gene. They have all proved to be chestnut based & breed as one would expect of chestnut ponies. The mushroom colour appears to be a variation in chestnut & a recessive gene so only occurs when two ponies that carry the gene are mated. It can be carried unseen for a number of generations so coming as a surprise to breeders when a mushroom foal is born unexpectedly.

Recognition
Some years ago, while looking through some U.K. Shetland pony stud books, I came across some entries for "mushroom" coloured foals. Intriguing, but it was not until a couple of years later that I realised that these entries would become so significant.

In the expansion of my Shetland pony herd, I purchased several ponies. Among these were a cream chestnut dun stallion, Firth Honeyclover and a cream chestnut dun filly, Grimpowood Tammy. The first foal from this pair, initially appeared to be a pale cream chestnut dun filly, but as she coated out, she became much paler in colour, almost resembling a cream foal. The following year, a chestnut mare of my own breeding produced a foal by Honeyclover that appeared palomino. A palomino was impossible, there being no crème gene in the pedigree at all. More of these foals followed over the years and I began to research the colour more thoroughly.

Letters, photos & hair samples were sent to acknowledged authorities all over the world but no-one could tell me what this colour was. Suggestions were put forward but none seems to fit the results from my own herd which bred as one would expect of chestnut ponies. 
 

Cream chestnut dun (left) & mushroom (right) showing the difference in colour.

Adult colour.
The typical mushroom coloured pony is a fawn or taupe colour with near white mane & tail but some may be much darker & appear brown with near white or silver mane & tail. Lower legs are the same colour as the body or light flaxen. Although ‘black’ hairs may develop in the mane & tail as with other chestnut based colours, the mane, tail & lower legs are never black. The summer coat seems to be generally much the same colour as the winter coat in ponies that live outside. When the new coat grows in, it seems to be a little darker than the old coat but fades very quickly, regardless of the weather. Often, if the pony has a long thick mane, the coat colour underneath the mane is much darker. The paler mushrooms seem to have paler roots to the hair while the darker coats have a greyish root to the hair. Some have a very light coloured mane & tail while others have a lot of dark, near black, & silver hair through the mane & tail. Some of these ponies have white ticking through the body coat. The true shade seems very difficult to capture in photographs as different light makes the coat appear a different shade & looking at the pony at different angles alters the perceived shade. Some of these ponies are a very pale beige, as in a young mushroom of the fungus type, some much darker in colour, as in an older mushroom. Hoof colour varies. Some are black, some horn colour & some have varying degrees of white stripes although there may be no white leg markings.

Mushroom must not be confused with cream chestnut dun or chestnut dun which have a yellow or orange tint to the coat. The important part of identification is the absence of any hint of red in the coat. The coats all have a rather faded look as opposed to the intense, shiny colour of the normal base colour coat. It is as if someone has removed all the red from the colour pigment. The darker mushrooms sometime show creamy ends to the long guard hairs & pony's beard. The skin colour of my own mushrooms seems to be mainly grey in colour. In some, there is a degree of mottling around the dock area but nothing really unusual. Many of these mushrooms have flaxen manes & tails &, in the dun forms, the eel stripe is sometimes missing from the mane & tail, although present as a liver dorsal stripe. However, there are some darker mushrooms that have darker manes & tails that have silver hairs through them. They seem to vary greatly in the same way that shades of chestnut vary from a pale red to a dark liver shade.

An equine vet has looked at the eyes of some of my mushrooms. So far, they appear to lack pigment at the back of the eye, so their eyes resemble the eyes of a chocolate Labrador dog. 

 Note. Mushroom may be found in dun, roan or pied combinations. In the dun form, the dorsal stripe is usually a liver colour.

 I researched some of the more common lines where these foals appear & give some examples on the following pages. Some lines are chestnut bred for several generations with no unexpected bays or browns (as would be expected if the silver gene was present). Other mushrooms have appeared from a black to black mating.  All appear sporadically &  in low numbers, a mare perhaps only producing one in a life time depending on whether the stallion used carries the mushroom gene or not. Breeding mushroom to mushroom has produced mushroom coloured foals only. The recent research carried out by Dr. Rebecca Bellone shows that homozygous (2 copies of the gene) mushroom appears as mushroom colour in a chestnut base pony. Heterozygous (1 copy of the gene) does not usually show in a pony.
 

The silver gene has been identified as being connected with a particularly nasty eye problem, Anterior Segment Disorder (ASD), also known as Multiple Congenital Ocular Anomalies Syndrome (MCOAS). Heterozygous silver-coloured equines have eye cysts & may be myopic while homozygous silver shows cysts & severe deformities of the eye.

Hair samples left to right: 1) Barclay Arms Wilma body, then, 2) Wilma under mane so not faded; 3) light chestnut; 4) dark chestnut; 5) April Girl of Clonyard body and 6) April under mane where it does not fade. When looking at these samples, it must be remembered that one sees only the tips when viewing any pony. For photos of these ponies, see next page, 'Houlland Connection'.
 

The mushroom colour blends superbly with surrounding dead grass which makes perfect camouflage.
 

EQUINE COLOR GENETICS

Note: A chapter on the mushroom colour, giving more details, is given in Professor Sponenberg's book "Equine Color Genetics", published in February 2009. This book should be obtainable through Amazon.co.uk or other on-line book stores.

Text & photographs on all Mushroom pages are copyright of Beth  Mead unless otherwise stated  

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