Final answer:
Lethal White Syndrome (LWS) in foals causes severe constipation due to a non-functioning colon and can lead to death within days of birth. Among the provided options, constipation is the clinical sign associated with LWS. Ataxia, regurgitation, and anhydrosis are not typical symptoms of this syndrome.
Step-by-step explanation:
The condition you are referring to is called Lethal White Syndrome (LWS), which is a genetic disorder found in horses, particularly in the Paint horse breed. Foals with Lethal White Syndrome are born with a non-functioning colon due to a genetic mutation, and this leads to severe constipation and an inability to pass feces. Other clinical signs of LWS might include colic due to intestinal obstruction, and unfortunately, affected foals typically die within a few days of birth.
Health issues that may be observed in LWS include anemia, edema, enlarged liver or spleen, and hydrops. None of the other symptoms listed - ataxia, regurgitation, or anhydrosis - are typically associated with Lethal White Syndrome in foals. Therefore, among the options provided, constipation would be the clinical sign you would expect to see in a foal affected by LWS.