Abstract

Cardiovascular disease is the leading cause of morbidity and mortality in captive western lowland gorillas (Gorilla gorilla gorilla), accounting for 41% of all deaths in adult gorillas.^1,2 Since many of these deaths are from potentially treatable causes, the Gorilla Species Survival Plan (SSP) recommends that all captive adult gorillas undergo regular cardiovascular exams. Although many zoos currently perform cardiovascular examinations, the data remains scattered throughout the country stored in institutional archives, inaccessible to the animal care community as a whole. At this time, no normal ranges are readily available for gorilla cardiac parameters to help determine which animals have subclinical disease. The National Gorilla Cardiac Database is an ongoing effort to gather and evaluate cardiac values for clinically healthy gorillas of different ages and sexes in order to create species-specific reference ranges. The database will serve as a reference tool for zoos when evaluating cardiac parameters in gorillas.

Echocardiograms from 33 gorillas submitted by ten zoos were analyzed by Dr. Ilana Kutinsky. Animals were excluded from the database due to findings consistent with severe cardiac disease (n=3) or due to unspecified age and/or sex (n=2). The remaining 28 echocardiograms were included in the database (see Tables 1–3). All echocardiograms were obtained from anesthetized gorillas. Anesthesia was usually induced using tiletamine hydrochloride and zolazepam hydrochloride (Fort Dodge Animal Health, Fort Dodge, IA, USA) and/or ketamine hydrochloride (Fort Dodge Animal Health, Fort Dodge, IA, USA) and maintained via isoflurane (Halocarbon Laboratories, River Edge, NJ, USA) or sevoflurane (Abbott Laboratories, Abbott Park, IL, USA).

Table 1. Physiologic parameters in western lowland gorillas (Gorilla gorilla gorilla) by age and sex

Table 2. Cardiac measurements in western lowland gorillas (Gorilla gorilla gorilla) by age and sex

Table 3a. Dynamic cardiac measurements in western lowland gorilla (Gorilla gorilla gorilla) by age and sex

Table 3b. Dynamic cardiac measurements in western lowland gorilla (Gorilla gorilla gorilla) by age and sex (continued)

Since many zoo veterinarians consult with medical cardiologists on gorilla cardiac evaluations, generalizations regarding gorilla cardiac health are often made using human reference ranges for echocardiographic parameters. Data collected in gorillas to date indicate that resting heart rates and blood pressure measurements are on average faster and higher than humans. Gorilla heart walls appear thicker and more dynamic than humans, supporting the contention that gorillas may have a higher resting sympathetic tone. Further investigation is needed to determine whether these increased parameters are a normal physiologic variation specific to gorillas or represent a response to physiologic stressors possibly induced by captive husbandry conditions.

Using this project as a foundation, further investigations should identify the predisposing risk factors for cardiovascular disease in gorillas, identify gorillas most at risk, implement and assess possible preventive measures, and develop recommended treatment guidelines for affected animals. The objective is to decrease the high prevalence of cardiovascular morbidity and mortality in captive gorillas, thereby improving the quality of life in individual animals and increasing the reproductive viability and genetic contribution of individuals to the collective gene pool of this endangered species.

Acknowledgments

The authors thank the following zoos for their participation in this project: Audubon Zoo, Cheyenne Mountain Zoo, Denver Zoological Gardens, Detroit Zoological Park, Gladys Porter Zoo, Knoxville Zoological Gardens, Little Rock Zoo, Milwaukee County Zoo Gardens, Omaha’s Henry Doorly Zoo, Smithsonian National Zoological Park, The Toledo Zoo, Zoo New England.

The authors urge additional zoos to submit data. To contribute to the gorilla cardiac database, please contact Dr. Hayley Murphy, Director of Veterinary Medicine, Zoo New England, Boston, Massachusetts, USA. Telephone: 617-989-2050, Fax 617-989-2080, email: hmurphy@zoonewengland.com.

Literature Cited

1.  Meehan T.P., and L.J. Lowenstine. 1994. Causes of mortality in captive lowland gorillas: a survey of the SSP population. Proc. Am. Assoc. Zoo Vet. Annu. Meet. 216–218.

2.  Ogden J., and D. Wharton. 1997. Management of gorillas in captivity. In: Gorilla Species Survival Plan Husbandry Manual. Pp: 157–158.