Which symptom is typically associated with a severe infestation of Haemonchus contortus in goats?

Submandibular edema is a symptom that typically signifies a severe infestation of Haemonchus contortus, commonly known as the barber pole worm, in goats. This condition arises due to the significant blood loss caused by the adult worms feeding on the host's blood. The resulting anemia can lead to a drop in protein levels in the blood, particularly albumin, which is essential for maintaining osmotic pressure. When osmotic pressure is disrupted, fluid can accumulate and cause swelling in the submandibular region, leading to the characteristic "bottle jaw" appearance observed in affected goats.

On the other hand, pneumonia is not a direct symptom of Haemonchus contortus infestation, although infected goats may develop other unrelated respiratory issues that could lead to pneumonia. Weight gain is generally counterintuitive, as a severe infestation typically causes weight loss due to the effects of parasitism, including loss of appetite and anemia. Fever can occur as a reaction to various infections or stressors, but it is not specifically indicative of Haemonchus contortus infestation. Thus, submandibular edema stands out as the key symptom associated with severe cases of this parasite.