Swayback, also known clinically as

lordosis Lordosis is historically defined as an ''abnormal'' inward curvature of the lumbar spine. However, the terms ''lordosis'' and ''lordotic'' are also used to refer to the normal inward curvature of the lumbar and cervical regions of the human spi ...

, refers to abnormal bent-back postures in humans and in quadrupeds, especially horses. Extreme lordosis can cause physical damage to the spinal cord and associated ligaments and tendons which can lead to severe pain. Moderate lordosis does not generally impact a horse’s usefulness and does not necessarily cause lameness.

Humans

Swayback posture in humans is characterised by the posterior displacement of the rib cage in comparison to the pelvis. It looks like the person has a hyperextension of the lower back, however this is not necessarily the case. Most sway-back exhibits a posteriorly tilted pelvis; the lumbar region is usually flat (too flexed) and not hyperlordotic (too extended).

Horses

Usually called "swayback", soft back, or low back, an excessive downward bend in the

back The human back, also called the dorsum, is the large posterior area of the human body, rising from the top of the buttocks to the back of the neck. It is the surface of the body opposite from the chest and the abdomen. The vertebral column run ...

is an undesirable conformation trait. Swayback is caused in part from a loss of muscle tone in both the back and abdominal muscles, plus a weakening and stretching of the ligaments. As in humans, it may be influenced by bearing young; it is sometimes seen in a

broodmare A mare is an adult female horse or other equine. In most cases, a mare is a female horse over the age of three, and a filly is a female horse three and younger. In Thoroughbred horse racing, a mare is defined as a female horse more than four ...

that has had multiple foals. However, it is also common in older horses whose age leads to loss of muscle tone and stretched ligaments. It also occurs due to overuse or injury to the muscles and ligaments from excess work or loads, or from premature

work Work may refer to: * Work (human activity), intentional activity people perform to support themselves, others, or the community ** Manual labour, physical work done by humans ** House work, housework, or homemaking ** Working animal, an animal tr ...

placed upon an immature animal. Equines with too long a

are more prone to the condition than those with a short back, but as a longer back is also linked to smoother gaits, the trait is sometimes encouraged by

selective breeding Selective breeding (also called artificial selection) is the process by which humans use animal breeding and plant breeding to selectively develop particular phenotypic traits (characteristics) by choosing which typically animal or plant mal ...

. It has been found to have a hereditary basis in the

American Saddlebred The American Saddlebred is a horse breed from the United States. This breed is referred to as the "Horse America Made". Descended from riding-type horses bred at the time of the American Revolution, the American Saddlebred includes the Nar ...

breed, transmitted via a

recessive gene In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant and t ...

. Research into the genetics underlying the condition has several values beyond just the Saddlebred breed as it may "serve as a model for investigating congenital skeletal deformities in horses and other species."Oke, Stacey. "Genetics of Swayback in Saddlebred Horses Examined" ''The Horse'' online edition, December 20, 2010. Accessed December 21, 2010
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References

{{Reflist Deforming dorsopathies Congenital disorders of musculoskeletal system Horse diseases

Humans

Horses

See also

References