Stillbirth rates across three ape species in accredited American zoos

Abstract

Stillbirths, or births of infants that died in the womb, represent a failure of the materno-feto-placental unit to maintain a suitable fetal environment. Typical studies of nonhuman primate (NHP) stillbirth patterns are primarily descriptive and focus on macaques (genus Macaca). Thus, less is known about other NHP species and rarer still are studies that examine possible biological factors that influence stillbirth rates across taxa. To examine possible contributors to stillbirths in great apes, we analyzed 36 years (1980-2016) of historical data documenting births of zoo-housed chimpanzees (Pan troglodytes, N = 391), western lowland gorillas (Gorilla gorilla gorilla, N = 491), and orangutans (Pongo spp, N = 307) in accredited zoological parks in the United States. The average number of births for each of the 446 mothers was 2.7, resulting in a total of 1,189 births with 143 stillbirths (12%). Stillbirths represented 12% of chimpanzee births, 13% of gorilla births, and 10% of orangutan births. We used generalized linear mixed-effects models to assess possible relationships between stillbirth likelihood and mother origin (wild- versus captive-born), age, and genus. Across taxa, older mothers were more likely to have a stillbirth (p = 0.004). While these results are likely influenced by both biological and management-related factors (e.g., selective captive breeding), they may be useful to population managers in evaluating pregnancy risks for great apes. Captive settings and archival studbook data such as these may provide a unique opportunity to further explore this topic.

A 25-Year Retrospective Review of Mortality in Chimpanzees (Pan troglodytes) in Accredited U.S. Zoos from a Management and Welfare Perspective

“…The stillbirth rate can also be calculated by referencing data from the chimpanzee studbook [ 63 ], which reports the total number of birth events during the study period (n = 147). Here, the stillbirth rate was 14.2%, which is very similar to the rate published over a slightly different timeframe (12%, [ 74 ]) and approximately equivalent to the rates demonstrated by other species of zoo-living great ape. Though some may question the welfare implications for stillborn infants, it is noted that for humans, the stillbirth prevalence has the potential for increased maternal morbidity risks and complications that may impact health and welfare [ 75 , 76 ], and similar risks for chimpanzees would be expected.…”

Comparative survival analyses among captive chimpanzees (Pan troglodytes) in America and Japan

“…While these comparisons are worthwhile, we must acknowledge that survivorship comparisons are complicated because of the difficulty in assessing early life mortality for wild chimpanzees, including stillbirths. We removed stillbirths from these analyses, but it is impossible to say how stillbirth rates in captive settings, documented at 12% for AZA (Saiyed et al, 2018) and 15% for Japan (Havercamp et al, 2019), compare to those experienced by wild-living chimpanzees.…”

Longevity and mortality of captive chimpanzees in Japan from 1921 to 2018

“…Almost one in six chimpanzees in Japan are stillborn. Of 391 chimpanzees born from 1980 to 2016 in North American AZA-accredited zoos, 48 (12%) were stillborn (Saiyed et al 2018). During the same time period, 63 of 415 (15%) infants in Japan were stillborn.…”

“…Studbook and other historical databases are excellent resources for the study of animal biology, care and management (Fisken et al 2018). Studbook data from accredited American zoos have previously been used to investigate chimpanzee birth timing (Wagner and Ross 2008) and great ape stillbirth rates (Saiyed et al 2018), and from European zoos to understand chimpanzee geographic origins and admixture (Hvilsom et al 2013). Few other databases exist such as AnAge (de Magalhães and Costa 2009), PanTHE-RIA (Jones et al 2009) and All The World's Primates (Rowe and Myers 2017), but captive data are still most commonly maintained in difficult-to-access national or regional studbooks.…”