North American Veterinary Licensing Examination (NAVLE) Practice Test

Which sign is a cardinal indicator of toxicoinfectious botulism in foals?

1. When startled, affected foals fall

2. Tongue hanging out, foal cannot retract it

3. Sawhorse stance

4. Hemorrhagic enterocolitis with head pressing

The correct answer is: Tongue hanging out, foal cannot retract it

The sign that serves as a cardinal indicator of toxicoinfectious botulism in foals is when the tongue hangs out and the foal cannot retract it. This occurs due to the neurotoxic effects of the botulinum toxin, which leads to muscle paralysis. In affected foals, the toxin disrupts the normal function of neuromuscular transmission, causing a loss of muscle tone and control. The inability to retract the tongue signifies weakness in the muscles responsible for tongue retraction, which is emblematic of the disorder. In comparison, the other options present signs that are either less specific or are more related to different conditions. For instance, falling when startled may indicate generalized weakness but is not uniquely associated with botulism. The sawhorse stance typically refers to a different condition where animals exhibit rigidity or tension, which does not specifically align with the hallmark symptoms of botulism. Lastly, hemorrhagic enterocolitis with head pressing has a different etiology that is not directly tied to the neurotoxic effects of botulism, further distinguishing it from the specific signs displayed in botulism cases. Thus, the hanging tongue is a distinct and critical symptom for identifying toxicoinfectious botulism in foals