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

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%).