What type of experiments would categorize an animal in category E according to the IACUC guidelines?

The correct categorization of an animal in category E according to IACUC guidelines pertains to situations where the animal experiences significant pain or distress that is not alleviated. Specifically, lethal dose experiments without intervention fall into this category because they involve administering a substance in a manner that intentionally leads to death, which clearly inflicts severe stress and suffering on the animal without any opportunity for relief or mitigation of pain.

In contrast, behavioral studies, routine health checks, and breeding experiments generally do not cause the extreme level of distress or harm that defines category E. Behavioral studies may involve observation that does not inflict harm, while routine health checks are designed to monitor and preserve animal welfare, and breeding experiments typically focus on normal reproductive processes that do not inherently lead to suffering. Thus, lethal dose experiments without intervention are classified under category E due to the high level of suffering they impose.