Which medication can be used to safely sedate a horse experiencing severe fear or anxiety?

Acepromazine is a phenothiazine tranquilizer commonly used to sedate horses during stressful situations. It works by calming the central nervous system and is particularly effective in reducing fear and anxiety, making it suitable for use in equine patients experiencing severe anxiety. Acepromazine provides sedation without causing respiratory depression, which is a crucial consideration in heavy sedation practices. This makes it a safe option to manage a horse's anxiety in various contexts, including veterinary examinations, transportation, or any situation where a horse may become overly stressed or frightened.

In contrast, other medications listed do not serve the same purpose. Alprazolam, while it is an anxiolytic, is not typically used in equine sedation and lacks research on effectiveness in this species. Phenobarbital is primarily an anticonvulsant and can have significant side effects, making it unsuitable for managing anxiety or fear in horses. Dexamethasone is a corticosteroid that is used to treat inflammation rather than for sedation purposes. Therefore, Acepromazine stands out as the most appropriate choice for safely sedation in horses experiencing severe fear or anxiety.