- Written by: Sharalee Worms
MCOA stands for Multiple Congenital Ocular Anomalies - it is a dominant disease
MCOA affects horses with the Silver coat color dilution. Horses that have two copies of the Silver gene are more sseverly affected and a wide range of eye defects are seen including underdevelopment of the iris, greatly enlarged eyes, small cysts in the eye and cataracts. Horses with only one Silver gene have less severe defects, usually just cysts..
Breeds that have been diagnosed with MCOA include the Rocky Mountain Horse (including the two related breeds Kentucky Mountain Saddle Horse and Mountain Pleasure Horse), Icelandics, Shetland Pony, Exmoor Pony, American Miniature, Belgian Draft, and Morgans.
- Written by: Sharalee Worms
CM is Congenital Myotonia - it is a recessive disease
Myotonia slows the relaxation of muscles after voluntary contraction or electrical stimulation this shows up as difficulty rising to the horses feet, abnormal vocalization, a stiff gait, and rigin dlimbs, neck and trunk.
Myotonia has been found in the New Forest Pony.
There is no effective treatment.
Genetic Testing is available.
Genetic Codes:
N/N The horse is normal, and cannot produce affected offspring.
N/cm This horse carries CM and will pass the allele on to approx. 50% of its foals. If bred to another N/cm carrier, approximately 25% of the offspring will be normal, 50% will be carriers, and 25% will be affected.
cm/cm The horse is affected with congenital Myotonia and will pass one copy of CM to every foal.
- Written by: Sharalee Worms
NFS stands for Naked Foal Syndrome
Foals are born with very sparse thin body hairs with little to no mane and tail hair. They don't live past 3 years of age and they have delayed growth. Their skin is dry and scaly in some areas and they have unusual tear activity..
So far NFS has only been found in the Akhal Teke breed.
- Written by: Sharalee Worms
ODSD means Ovotesticular Disorder of Sexual Development it is a dominant mutation
ODSD produces sterile females - it only comes from the stallion - all foals born are either normal colts or fillys that cannot have foals of their own.
- Written by: Sharalee Worms
SWO stands for Splashed White Overo - it is a recessive disorder
SWO is another coat pattern defect - it applies to patterns that determine white. Embryos that receive two of these genes will not complete development and will abort in the womb.
Hearing loss is associated with White Patterned horses - horses white on the inside of the ear are affected - horses who's ears have pigmented hair inside the ear are not affected.
Splashed White 2 (SW2) and Splashed White 3 (SW3) are found Quarter Horses and related breeds.
Genetic Codes:
| SW1/SW1 | Homozygous | Horse has two copies of the SW-1 mutation |
| N/SW1 | Heterozygous | Horse has one copy of the SW-1 mutation |
| N/N | Negative | No copies of SW-1 mutation |
| SW2/SW2 | Homozygous | Horse has two copies of the SW-2 mutation |
| N/SW2 | Heterozygous | Horse has one copy of the SW-2 mutation |
| N/N | Negative | No copies of SW-2 mutation |
| SW3/SW3 | Homozygous | Possible homozygous lethal |
| N/SW3 | Heterozygous | Horse has one copy of the SW-3 mutation |
| N/N | Negative | No copies of SW-3 mutation |
| SW4/SW4 | Homozygous | Possible homozygous lethal but no current information available |
| N/SW4 | Heterozygous | Horse has one copy of the SW-4 mutation |
| N/N | Negative | No copies of SW-4 mutation |