Lordosis (Swayback)

Lordosis, also known as swayback, is a curvature or dip in the spine that is often seen in older horses. However, in the American Saddlebred, this condition also affects younger horses. These animals do not appear to experience pain from their condition and are still able to be used under saddle. The genetics are likely complex and poorly understood.

One genome-wide study has been performed on lordosis in the ASB. The four markers tested here (L1-L4) achieved the highest association, with 23/30 swayback horses homozygous for all four associated alleles, and an additional 7 cases were heterozygous for all. In comparison, there were only 44/287 controls homozygous for all four, and 135/287 heterozygous. Thus, horses that genotype L1: T/T L2: G/G L3: T/T L4: G/G are considered most at risk for the lordosis phenotype. The researchers were unable to detect any candidate mutations in the three genes screened in closer detail. Further research is necessary to refine the association.

Publications

Cook D et al., “Genetics of swayback in American Saddlebred horses.” (2010) Anim Genet. 41 Suppl 2: 64-71. PMID: 21070278

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EZ Guide:  What do my test results mean?     Lordosis Test Key

                                          If      -/-, -/+, -/-, -/-   One    Lordosis allele detected - NO KNOWN AFFECT

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If     -/+, -/+, -/-, -/- Two    Lordosis alleles detected - NO KNOWN AFFECT

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If      +/+, +/-, -/-, -/- Three Lordosis alleles detected - NO KNOWN AFFECT

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If      +/+, +/+, -/-, -/- Four Lordosis alleles detected; non-consecutive - NO KNOWN EFFECT

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If      +/-, +/-, +/-, +/- Four Lordosis alleles detected; CONSECUTIVE - CARRIER STATUS          

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If      +/+, +/+, +/+, +/+ Eight Lordosis alleles detected; CONSECUTIVE - LIKELY AFFECTED STATUS

(POSSIBLE LORDOSIS APPEARANCE 80% LIKELY, MAY PASS ALLELES TO 100% OF ANY OFFSPRING)