Final answer:
The best method to assess pain in a ferret post-adrenalectomy is to observe its behavior for signs of distress and apply a ferret-specific pain scale.
Step-by-step explanation:
The best way to determine whether a ferret that has received an adrenalectomy needs analgesics is to observe its behavior for distress signs. By monitoring its behavior, you can look for signs of pain such as reluctance to move, changes in normal behavior, vocalizations, or changes in eating habits.
Additionally, the use of a pain scale specifically designed for ferrets can provide a more systematic and objective way to assess the ferret's experience of pain and therefore determine the need for analgesics. While blood tests, measuring body temperature, and observing physical changes like increased muscle activity or changes in insulation can provide general health information, they are not as direct or specific in assessing pain as behavioral observation and pain scales are.