Problems associated with long-term feeding of purified diets in rhesus monkeys

Although non-human primates are widely used models of human diseases, often studied for long periods of time, their dietary requirements are not well defined. Over a two-three-year time period, female rhesus macaques were fed either a marginally zinc-deprived diet or a comparable zinc replete purified diet. The purified diets were based on current NRC recommendations. Interestingly poor pregnancy outcome was noted in both the zinc-deprived as well as in the control group. Twenty-eight percent of controls (N=16) and 20% of zinc-deprived animals (N=15) failed to conceive after at least seven matings. Pregnancy loss was also high in both groups of animals including 31% of conceptions in controls (N=11) and 33% of conceptions in zinc deficient animals (N=12). The majority of pregnancy losses occurred after animals had been fed purified diet for over two years. In contrast, normal colony pregnancy loss is estimated at 11%. Furthermore, 3 of 18 live-born infants died prior to 7 months of age and one third of surviving offspring were growth-retarded during the 1st year of life compared to established colony norms. Our data demonstrate the difficulty of constructing adequate purified diets for long-term studies in primates even when based upon available and recommended nutritional information.