Breeding Psychology Breeding Selective Traits

¶ … Breeding Psychology Breeding selective traits in animals: Negative traits in Paint horses Scientists frequently try to breed selective traits in animals for research purposes, as in the case of mice bred for their propensity to become addicted to alcohol. However, this is only one example of a trend which has had a long history in humanity's relationship with the animal world. Breeding animals to manifest select traits has been common since early humans engaged in agricultural production.

Today, some traits in horses are occasionally selected for efficacy in sporting activities, others for appearance. Selective breeding is used to predictably produce such traits, just as speed in Thoroughbreds, agility in cutting horses, and jumping ability in Warmbloods. Other examples include special 'colored' horses such as palominos and Paint horses (Grandin 1998). However, breeding for one type of desirable trait can occasionally cause the manifestation of a connected, yet undesirable trait. "Genetic traits are linked in complex ways. Over-selecting animals for physical traits often causes changes in behavior.

Likewise, over-selection for behavioral traits can cause corresponding changes in physical traits" (Grandin 1994). Such is the case in breeding Paint horses, in which exaggeratedly large white patches with underlying pink skin called 'piebalding' is considered particularly attractive and desirable. Animals with "large piebald spots on the head and body may have neurological defects similar to the genetic defect known in humans as piebaldism. The piebald condition is linked to defects in both the visual system and in hearing" (Grandin 1995).

Piebald spots do not always signal neurological defects and not all Paints have piebald spots. But breeding two Paint Horses who have large areas of piebald patches can produce problematic results. For example, nervousness is common in animals with large piebald areas. Animal behaviorist Temple Grandin notes she "observed some extremely abnormal behavior in a highly depigmented Paint stallion at a horse show. The stallion was so distressed by the sights and sounds of the show that he was literally eating up his stall.

This behavior was in sharp contrast to the normal behavior shown by a frightened horse" (Grandin 1994). These horses also exhibit balance problems due to defects in the inner ear, confirming a relatively old adage among horsemen: "Four white feet, pass him by" (Grandin 1994). Another problem associated with Paint horses is 'lethal white' syndrome, in which Paint mares give birth to white foals that are unable to pass feces and die shortly after birth.

"The mutated gene alters neural crest cell migration or survival, which affects the progenitor cells for melanocytes and intestinal ganglia. Affected foals suffer from aganglionosis of the submucosal and myenteric ganglia of the distal part of the small intestine and of the large intestine, resulting in intestinal immotility and colic" (Lightbody 2002).

According to genetic research conducted through the Minnesota Paint Horse Association, it was found that of 100 horses that produced lethal white syndrome foals, all OLWS (Overo Lethal White Syndrome) foals had two lethal alleles, their parents had a normal and a lethal allele, and control group of solid-colored horses all had two non-lethal alleles (Vrotsos & Santschi 1998). However, unlike the more general 'nervousness' associated with piebald characteristics; the lethal white trait can be more easily isolated.

Because of the inability of the affected foals to reproduce, "the probability of producing an OLWS offspring is less than 25%" (Lightbody 2002). A DNA-based test exists that can identify identifies horses that are heterozygous for the lethal white gene "The allele-specific polymerase chain reaction test locates and amplifies the specific mutated site in the endothelin receptor B. gene (EDNRB gene)" (Lightbody 2002). However, temperamental.