Inappetence is one of the most common clinical signs in laboratory and privately owned animals. It is a welfare concern, especially in rabbits, Oryctolagus cuniculus, as inappetence can lead to gastrointestinal stasis and death. There are numerous causes of inappetence in rabbits, including but not limited to stress, pain, systemic disease, poor diet, and the use of opioids to treat or control pain. Currently, there is no standard treatment for inappetence in rabbits. Mirtazapine, a tetracyclic antidepressant has been used anecdotally as an appetite stimulant in rabbits. A newer drug capromorelin (Entyce), a ghrelin receptor agonist, was recently evaluated by our lab in a pilot study to assess its effect on appetite in healthy New Zealand White (NZW) rabbits. This data showed that capromorelin given once daily for three days increased feed intake significantly (p = 0.018) compared to oral sterile water control.

In this proposed study, we aim to assess the effects of capromorelin and mirtazapine on appetite in rabbits. Efficacy of two doses of each appetite stimulant will be assessed by measuring daily feed intake, daily fecal output, and bi-weekly body weights in a randomized crossover study. The rabbits will receive seven treatments: control (saline), capromorelin 4 mg/kg administered by mouth once a day, capromorelin 8 mg/kg administered by mouth once a day, capromorelin 4 mg/kg administered by mouth twice a day, capromorelin 8 mg/kg administered by mouth twice a day, mirtazapine 0.5 mg/kg transdermal once a day, and mirtazapine 1 mg/kg transdermal once a day for 3 days, with a 11-day washout period between treatments. Transdermal mirtazapine was chosen versus oral mirtazapine due to ease of administration. Feed intake and fecal output will be monitored once daily and body weight biweekly. The rabbits will also be monitored daily for adverse effects such as signs of decreased feed or water intake, decreased fecal output, change in behavior, and decreased body condition. To our knowledge, this is the first study comparing the effect of capromorelin and mirtazapine on appetite in rabbits.