Final answer:
In a foal with lethal white syndrome (LWS), the expected clinical sign is regurgitation due to an underdeveloped intestine and related complications. This genetic disorder also leads to constipation and is unfortunately fatal.
Step-by-step explanation:
The question pertains to a clinical condition that could be observed in a newborn Paint horse foal with lethal white syndrome. The correct clinical sign you would expect to see in a foal with lethal white syndrome among the options provided is regurgitation.
Lethal white syndrome (LWS), also known as overo-lethal white syndrome (OLWS), is a genetic disorder that affects certain breeds of horses, leading to a non-functioning colon. This condition is characterized by foals being born with an all-white or nearly all-white coat and blue eyes. Despite the striking appearance, these foals typically cannot pass feces, which leads to constipation, and as a result, to distension of the abdomen and colic. They also show signs of regurgitation due to an underdeveloped intestine and related complications. Unfortunately, lethal white syndrome is fatal, and affected foals typically die within a few days of birth due to complications related to an inability to pass feces and subsequent toxin buildup. Important to note is that this condition is genetically inherited and is linked to a mutation of the EDNRB gene. It's exclusively seen in the offspring of certain lines of Paint horses where both parents carry the specific gene mutation.