Kentucky Mountain Saddle Horse
News
Sept/Oct 2006
Great Gaits
by: Barbara Weatherwax
Spotted Mountain Horses
The “Sports Models” of the
Mountain Horse Family
Part 2
(Part 1,
July/August issue)
There are several terms associated
with the Spotted Mountain Horse which are useful to know. TOVERO is
a cross between tobiano and overo. PIEBALD is always black and white
– in tobiano, overo and Sabino. SKEWBALD is any combination of color
other than black and white. Both palomino and white, and bay and
white would be considered skewbald. CALICO is usually found in overo
and Sabino horses that are roan and spotty white. REBECANO (also
known as Squaw Tail) describes white at the base of an otherwise
colored tail. It is most common in overo coloring. DISTAL or ERMINE
spots are roanish spotted edging around a dark colored spot. Skin
under these edgings will be dark. INK SPOTS are dark skin spots with
white hair covering them. They are usually found in large white
spots and sometimes found on the legs of high-stockinged horses.
These spots are sometimes referred to as “spots on spots.” TODAINIAN
is a color pattern found in tobiano horses. It is white over the
back and the hind quarters.
WALL
EYES, CHINA EYES, and GLASS EYES are all terms describing blue eyes,
which are a frequent characteristic in spotted horses. The blue
pattern does not impair vision.
Genetic study of the multicolored
horse has made tremendous advances in recent years. There are
definite “recipes” determining “get.”
The sire contributes 50% or one gene
to the foal and the dam contributes the other 50% or one gene.
The tobiano gene is dominant. If the
sire has a tobiano gene T and a non-tobiano gene t,
and the dam has the same combination, there are only four possible
combinations.
1) sire T
dam T
2) sire T
dam t
3) sire T
dam t
4) sire t
dam t
Since T is dominant, the get
from 1, 2, and 3 would be tobiano. The product of 4 would not be
tobiano. So the chances of getting tobiano from such parents would
be 3 out of 4.
The overo gene is recessive. The
horse must have two overo genes before it will display the overo
pattern. If the sire has a non-overo gene O and an overo
gene o, and the dam has two overo genes oo, the four
possibilities would be
1) sire O
dam o
2) sire O
dam o
3) sire o
dam o and
4) sire o
dam o
There would be a 50-50 chance of
producing an overo foal: 3) and 4) would be overo, and 1) and 2)
would not. Unfortunately, there is no blood test to identify
the overo gene in advance. Trial and error has validated the
formula.
HETEROZYGOUS and HOMOZYGOUS are two
other terms that are part of the Spotted experience. Heterozygous
is designated by the symbol Tt and it means the tobiano horse
will produce tobiano offspring 50% of the time. When the tobiano
gene T is passed to offspring, the resulting foal will be
tobiano. When the solid color gene t is passed to offspring,
the resulting foal will be solid color. Most tobiano horses are
heterozygous.
Homozygous is designated by the
symbol TT and it means the tobiano horse will produce tobiano
offspring 100% of the time. The homozygous horse has no other gene
to give the offspring. In breeding practice, if a horse produces or
sires a solid-colored foal, the horse is heterozygous.
The homozygous horse is very valuable
in Spotted Mountain Horse breeding programs. Homozygous foals are
produced by breeding a tobiano to tobiano. Of this mating, 25% of
foals will be solid, 50% will be heterozygous tobiano and 25% will
be homozygous tobiano.
So there’s a lot to be proud of in
our Spotted Mountain Horses. They truly complete the family of
KMSHA.
