• Hello, Vetaheader! Our monthly newsletter is here. This time, we are all about rabbits! 🐰

Second, we have a study comparing the effects of carpromelin and mirtazapine on the appetite of rabbits (side note: this paper has been published with full access!). Inappetence is a welfare concern in rabbits, as it can lead to GI syndrome (a.k.a. GI stasis, ileus); even so, few published studies have evaluated the efficacy of appetite stimulants in rabbits. This paper covers two different studies.

In the first study, 9 healthy rabbits were evaluated using a randomized crossover design and 9 treatments, with 3 days of duration each, with a one week washout period between them. The details are below:

• Capromorelin: 4 mg/kg PO q24h, 8 mg/kg PO q24h, saline control PO q24h

• Capromorelin: 4 mg/kg PO q12h, 8 mg/kg PO q12h, saline control PO q12h

• Mirtazapine: 0.5 mg/kg transdermal (TD) q24h, mirtazapine 1 mg/kg TD q24h, and saline control TD q24h

Note that the TD mirtazapine was applied using a 1 mL syringe, and the researchers used gloves to protect them from absorption. The medication was applied in alternate ears each day, and the ears were not cleaned or shaved before application. Treatment efficacy was assessed by measuring daily feed intake and fecal output and by weighing rabbits twice a week. The rabbits in the capromelin q12h groups and the ones in the mirtazapine groups had higher feed intake and fecal output when compared to the control groups; rabbits in the mirtazapine groups had the highest scores in feed  intake and fecal output. However, erythema and petechiae of the pinnae were observed in animals receiving TD mirtazapine, particularly the ones on the 1 mg/kg treatment.

In the second study, seven rabbits were submitted to orchiectomy, and received one of three treatments for three days, post-op: capromorelin (8 mg/kg PO q12h), mirtazapine (1 mg/kg TD q24h), or saline (PO q12h). The animals also received buprenorphine (0.03 mg/kg SC q 6-8 h) and meloxicam (1 mg/kg PO q 24 hr) for three days. This time, feed intake and fecal output for the mirtazapine group were not significantly different from those of the capromorelin and control groups. It was noted that the rabbits did not like taste of capromorelin.

So, the take home is that capromorelin (4 mg/kg PO q 24 hours) or mirtazapine (0.5 or 1 mg/kg transdermal q 24 hours) can be used in rabbits. Mirtazapine appears to be more effective, but the transdermal route may lead to erythema and/or petechiae.

Lastly, we have a retrospective study on the age and cause of death of pet rabbits seen at a clinic in Tokyo. The data compiled information from 2006 to 2020, amounting to 898 cases. Previous studies have focused primarily on age of rabbits when surveys were taken; however, this one focused on the age at death.

• Netherland Dwarf: 7 YO
• Holland Lop 6 YO
• French Lop 5 YO
• Flemish Giant 3 YO

Overall, smaller breeds had higher average ages of death. The main causes of death included neoplasia (n=223; 24.8%), GI disease (n=135; 15.0%), bacterial abscess (n=90; 10.0%), urinary disease (n=85; 9.5%), trauma (n=44; 4.9%), and cardiac disease (n=27; 3.0%). Age influenced on the most common cause of death:

• 4 YO or less: GI disease (32%)

• 5-15 YO: neoplasia (12.5-100%)

• 13 YO rabbits: GI disease (25%) and neoplasia (17%)

Previous studies from England and Netherlands found average life span of 4.2-5.6 YO – this may be due to housing conditions, which are usually outdoors in Europe, or vet clinic types (primary vs. secondary). Also, it was discussed that the negative attitudes towards euthanasia in Japan may have elevated the average age.

Take home message: median age at death in rabbits in Japan was 7 YO, and 18% of rabbits lived beyond 9 YO. Common causes of death were neoplasms, GI disease, bacterial abscesses, and urinary diseases.