Retrospective Analysis of the Incidence of Retained Placenta in 3 Large Colonies of NHP

During 1999 through 2014, retained placenta was the most common cause of clinical admission for reproductive complications in breeding colonies of baboons (approximate colony size, 2000 animals), cynomolgus macaques (approximately 1000), and rhesus macaques (approximately 500) at the Southwest National Primate Research Center. Retained placentas occurred in 2.7% of baboons, 3.3% of cynomolgus macaques, and 1.0% of rhesus macaques. Apparent risk factors for retained placenta included stillbirth or abortion and at least one prior cesarean section. There was a significant association between stillbirth and retained placenta in all species. Cesarean sections were performed routinely for baboons to meet research objectives but occurred only as needed for cynomolgus and rhesus macaques. Having had at least one prior cesarean section was an incidence factor for retained placenta in 37.0% of baboons and 4.7% of cynomolgus macaques; none of the rhesus macaques with retained placentas had undergone cesarean section previously. More than 90% of dams with retained placenta returned to a successful reproductive life or assignment to a nonbreeding research protocol. Advances in reproductive management will benefit from prospective studies that capture additional data from all members of a breeding group prior to reproductive complications.Abbreviations: Southwest National Primate Research Center (SNPRC), retained placenta (RP), cesarean section (C-section)Retained placentas and other reproductive problems are unavoidable complications encountered in association with NHP production colonies and are difficult to diagnose, because most births occur at night, when human observation is minimal, and because the dams routinely consume the placenta.^41,44,45 There is extensive information regarding retained placentas in dairy cattle,^7,25,20 and humans,^{3,13,24,35,36,40} but little is documented about this problem''s health hazard and effect on future reproduction in NHP,^16,17,23,49 with 3 documented cases reported as isolated reports between 1991 and 2009.^16,17,23 The first documented case of a retained placenta in a NHP was that of a female chimpanzee (Pan troglodytes).¹⁷ Clinical signs for that case included depression, poor maternal care, and vaginal hemorrhage 1 wk after delivery. The chimpanzee was treated successfully, and the infant was returned to the dam with no further complications. Another documented case involved a golden lion tamarin (Leontopithecus rosalia),¹⁶ which had experienced prolonged labor resulting in a stillbirth. After continued placental retention, the tamarin was hysterectomized. Histopathologic evaluation revealed that placental infiltration into the myometrium was the cause of retention.¹⁶ The third documented case occurred in a bonobo (Pan paniscus) housed in a sanctuary in the Democratic Republic of Congo.²³ The animal was treated with oxytocin injections; after manual removal of the placenta, the dam and infant were reunited, and maternal recovery was uneventful.In addition, in an unpublished case, one of the current authors (TH) treated a mandrill (Mandrillus sphinx) by using oxytocin injection and manual removal of the placenta, after which the dam and infant were reunited, and maternal recovery was uneventful. Several other unpublished cases documented in the medical records of the breeding colonies at the Southwest National Primate Research Center (SNPRC) involved species baboons (Papio spp.), cynomolgus macaques (Macaca fascicularis), and rhesus macaques (Macaca mulatta). Clinical veterinarians had deemed all of these animals to be healthy prior to their placement into breeding groups and were rechecked semiannually concurrent with tuberculin testing. Body condition varied from lean to obese, but body condition score was not recorded. We retrospectively reviewed these records to determine the risk factors and incidence of retained placenta within the 3 NHP colonies over 15 y.