Congenital and hereditary anomalies in the rhesus monkeys (Macaca mulatta) of Cayo Santiago

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Abstract
During seven annual birth seasons, from January 1976 to July 1982, 963 infants were born in the Cayo Santiago, Puerto Rico, colony of free-ranging rhesus monkeys (Macaca mulatta). The reproductive rate for mature females, 4 years of age and older, ranged between 74.1% and 84.7%, with a cumulative mean of 80.8% over 7 years. Live births comprised 95.3% of the total and the secondary sex ratio was 109 male to 100 female births. No twinning was observed. Aborted and stillborn monkeys represented 4.7% of all births. The percentage of stillborn females was greater than that of males (4.0% vs. 3.1%). Neonatal death, defined as mortality within 48 hours postpartum, occurred in 0.8% of the live births. Two cases of congenital abnormalities were observed. The first was an anencephalic, acranial female and the second a congenitally blind male. Both infants were born to matrilineally unrelated 7-and 8-year-old multiparous females with no prior history of delivering malformed offspring. The incidence of each defect, based on 963 births, was 0.10%, with a cumulative incidence of 0.20% for all teratisms seen during the study. Multiple occurrences of a rare, nonpathological and nonlethal hereditary anomaly were also seen. Five “golden” macaques were born into two genetically distinct social groups within the last 2 years of observation. The incidence of this phenotype, based on five cases, was 0.52%, 52 times the expected rate (.01).