Tobiano
Tobiano is a dominant pattern, which means that breeding two tobianos will usually result in a spotted foal; there are some tobianos which are homozygous, which means all breedings from this horse will result in a spotted foal. A DNA test is now available which will tell whether a tobiano is homozygous or not.
There are several distinctive characteristics of a tobiano:
• Tobianos almost always have a 'war shield' spot of color over the chest and shoulders plus a spot on each flank; occasionally only one flank spot is seen and very rarely, none.
• All tobianos have four white legs. Eighty percent have white markings on all four legs up to the knees/hocks or higher.
• Tobianos usually have facial markings like a solid horse, star, stripe, snip, etc.
• Most tobianos have mixed white and colored manes and tails or one of the two.
• The spots usually have even, non-jagged edges. They're usually smoother looking than overo patterns but this isn't always the case.
• Almost all tobianos have white extending over the backbone.
Overo
An Overo has distinctive characteristic:
• Overos have solid color over the backbone from the withers to the tail bone.
• They have spots that often have lots of tiny flecks of color or white nearby the edgings. Overos can have spots within spots a big jagged white spot with a colored jagged spots within.
• Many overos look as if their white spots spread from the belly up to the back.
• Facial markings, bonnet, apron and bald faces. Many overos also have 'beauty spots', which are little spots on the muzzle or lips.
• Most overos have solid manes and tails. Occasionally an overo will have white in its mane where a spot crossed over the neck, but only rare individuals will have half and half manes like tobianos.
• Most overos have at least one totally dark leg; many have no leg markings whatsoever. It's possible to find overos with four stockings but they're very uncommon.
Tovero
Is a mixture of Tobiano and Overo patterns. Below is a set of distinguishing characteristics
• Toveros often have a dark patch that covers the ears and at least the upper half of the horse’s head (Medicine Hat). They may also appear to be wearing makeup outlining their eyes and mouth. One or both eyes are usually blue and colored spots when apparent are found on the toveros flank and base of the tail.
• Overos with excessive white in the mane are suspect. Excessive white on all four legs is also an indication. Overos with a tobiano-like pattern but no white over the backbone are usually toveros and smooth looking spots are also a sign.
Sabino
Sabinos have characteristics very similar to overos, but are subtly different:
• Like overos, sabinos have solid color over the backbone from the withers to the tail bone. Their pattern spreads from belly and legs upward, but can usually be recognized by roaning in most cases, which is its main factor. Crisp-edged spots are also seen though, and this makes understanding the difference between those sabinos and overos confusing.
• Sabinos can show as little as only high whites to the extreme of nearly white with body flecking around the flanks, backbone, chest and ears.
• Sabinos show the same facial markings as overos.
• Sabinos usually have solid manes and tails, though the horses expressing stronger sabino traits often have white in their mane where roaning crossed over the neck; some sabinos have nearly white manes and tails, depending on how strongly the pattern is expressed.
• Unlike overos, sabinos often have four white legs; many "overos" with four white legs are usually sabinos or sabino crosses.
Mapping
This effect in horses occurs at the edges of spots where the white hair lays over the dark skin of the colored spots. Since white hair is more translucent than dark hair, you can sometimes see where the dark skin begins around the spots. Seen through the white hair, the dark skin appears grey or a lighter shade than the colored hair, and gives the spot a soft, 'mapped' color.
Breeding Patterns
Tobiano and overo are two separate patterns and are controlled by separate genes. In and of themselves, the genes have nothing to with each other. In certain matings, however, both patterns can be seen on the body of the foal. This combination is called "tovero". A tovero has been found to produce the highest amount of colored foals 80% the more white they have the higher the chance of producing a colored foal. Homozygous Tobianos have a 100% chance of producing a colored foal.
Overos can be produced from two non colored horses.
Overos crossed with Overos can produce Overo or Solid and if not tested Lethal white foals.
Tobianos crossed with Overos can produce four possible color patterns Tobiano, Overo, Solid or Tovero.
Tobianos crossed with Toveros can produce Tobiano, Solid, Overo and Tovero.
Toveros to Toveros can have Overo, Tovero, Tobiano and Solid.
Leathal White Overo
Overos can carry the lethal white gene and both Overos and Toveros should be tested for this before breeding.
A lethal White Foal is a foal who is born with no nerve cells in the intestinal tract. Food is ingested but is unable to be propelled through the gut for digestion. It is 100% fatal. Knowing your mares or stallions LWO status can allow you to prevent a foal of this type.
If your mare is a carrier of the gene It would not be wise to breed with another carrier. If two carriers are bred there is a 25% chance of producing a leathal white foal. 50% chance for them to be carriers and 25% chance they will not carry the gene. There is a genetic test for this genetic mutation and testing is recomended before breeding Overos or Toveros.
HYPP
HYPP is a muscular disease. It is caused by a hereditary genetic mutation that disrupts a protein called a sodium ion channel, a tiny gateway in the membrane of muscle cells. The mutation affects the channel's normal opening and closing, In effect uncontrolled sodium influxes occur. These influxes in turn change the voltage potential of muscle cells, causing uncontrolled muscle twitching or profound muscle weakness. High levels of potassium in the blood usually are present when the disruptions in the ion channel occur. Attacks are sudden and unpredictable and can lead to collapse and sudden death. The cause of death usually is cardiac arrest and/or respiratory failure. The disease is characterized by intermittent episodes of muscle tremors manifested by generalized or localized shaking, trembling and weakness. Occasionally, episodes are accompanied by respiratory noises resulting from paralysis of the muscles of the upper airway. The mutant gene causing HYPP presently has been identified in the descendants of the horse "Impressive". Currently there is a genetic test to determine the carrier status of HYPP if your horse is tested N/H it has the gene and the disease. This horse if bred will produce of spring with 50% of them being carriers with the disease. Some N/H horses can live without showing any signs of the disease. If your horse is tested N/N your horse does not have the genetic disease nor will they pass it on. They are totaly free of the genetic mutation.
HERDA
Hereditary equine regional dermal asthenia (HERDA) is a genetic skin disease associated with the Poco Bueno Bloodlines. HERDA is characterized by hyperextensible skin, scarring, and severe lesions along the back of affected horses. Affected foals rarely show symptoms at birth. The condition typically occurs by the age of two, most notably when the horse is first being broke to saddle. There is no cure and the majority of diagnosed horses are euthanized because they are unable to be ridden and inappropriate for future breeding. HERDA has an autosomal recessive mode of inheritance and affects stallions and mares in equal proportions. HERDA afflicted horses have a lack of adhesion within the dermis, the deep layer of skin, due to a collagen defect. Think of it like glue holding the skin layers together, only the glue is inferior. Because the layers are not held firmly together, they separate. When the horse is ridden under saddle or suffers trauma to the skin, the outer layer often splits or separates from the deeper layer, or it can tear off completely. It rarely heals without disfiguring scars. New damaged areas arise continuously, sometimes even without obvious trauma. There is a DNA test available for this genetic disease and having your horse tested, if they have the lineage associated with this disease, is recomended before breeding.
