A common cause of exercise intolerance in horses is equine recurrent laryngeal neuropathy (RLN). This is a fancy way of saying that the animals are not able to open their larynx on the left side very well during strenuous exercise, which limits their oxygen intake and ability to exercise. Larger horses, like thoroughbreds, are more prone to developing this condition than smaller breeds.
In a new study published in Physiological Genomics researchers explored whether there was a genetic link between height and RLN by testing blood samples collected from 458 Belgian Draft Horses; animals that are at greater risk of developing RLN than thoroughbreds. Their results confirmed the existence of a genetic link between height and RLN and identified two previously unknown genetic variations that are associated with these factors. Although the researchers were careful to point out that factors other than height are also likely correlated with risk for RLN as well.
Brooks SA, Stick J, Braman A, Palermo K, Robinson NE, Ainsworth DM. Identification of loci affecting sexually dimorphic patterns for height and recurrent laryngeal neuropathy risk in American Belgian Draft Horses. Physiological Genomics. 03 DEC 2018 https://doi.org/10.1152/physiolgenomics.00068.2018