pH. Supplementing with trivalent Cr in drinking water maintained at a mildly acidic pH was ineffective. Divalent Cr was not effective in improving glucose tolerance.

Martin et al. (1972) reported corneal opacities in eyes of adult female squirrel monkeys (Saimiri sciureus) weighing 600-800 g that were fed a semipurified diet containing Cr at 0.093 mg·kg-1 of DMand received drinking water with Cr at less than 0.01 mg·kg-1. Total intake of Cr was about 4 µg per animal per day. The mean daily food intake was 44 g. After 6 weeks on the deficient diet, eye lesions developed, starting as haziness of the cornea. The lesions developed into superficial maculae and progressed to deeper opacities with vascularization. The lesions were not reversible by Cr supplementation or the feeding of a commercial monkey diet for up to 9 months. Similar but milder lesions developed in squirrel monkeys fed the deficient diet for 2 weeks, then supplemented with trivalent chromium at 5 mg·kg-1 in the drinking water (total intake, about 400 µg per monkey per day). The results suggest that even a short-term dietary deficiency of Cr can lead to irreversible corneal lesions. Comparable lesions were not observed in animals maintained on diets similar in composition but higher in naturally occurring Cr or on a commercial monkey diet that furnished about 150 µg of Cr per day. Other than the eye lesions, the animals remained healthy over the 34-week period without any other signs of dietary deficiency.

Because of issues of biologic availability and the valence state of Cr (only trivalent and hexavalent chromium are biologically active), a quantitative requirement for Cr has not been established. The Cr content of the diet is thought to have little relationship to biologically active Cr, because of the diversity of dietary Cr forms (National Research Council, 1997). Chromium nutrition has not been studied in nonhuman primates other than squirrel monkeys.

Fluorine

Fluoride (F-) reduces the incidence and severity of dental caries in humans (Phipps, 1996). The caries-preventive effect of F- is attributed mainly to remineralization at the interface of teeth and oral fluids. F- in saliva shifts the balance from demineralization, that leads to caries, to remineralization, presumably because of the F--enhanced precipitation of calcium phosphates and formation of fluor-hydroxyapatite (ten Cate, 1999). It is now considered a required element in human diets because of its cariostatic effect, when it is ingested, on pre-eruptive development of teeth. F- in oral fluids also has a cariostatic effect on posteruptive teeth. The need for F- in humans is most commonly met by addition to the drinking water at 1.0 mg·L-1, which is considered an optimal concentration (Institute of Medicine, 1997).

Natural ingredients used in manufactured diets for primates can contribute substantial amounts of F-. Grains, oilseeds, and their byproducts frequently contain F- at 1-2 mg·kg-1. Animal and fish byproducts containing bone can contribute to dietary F-.F- is a common contaminant in rock phosphate, the source of much of the feed-grade phosphate used as a phosphorus supplement. To qualify as feed-grade phosphate, it must be deflourinated to 1 part of F- (or less) to 100 parts of phosphorus (AAFCO, 1997). Depending on the manufacturing process, the addition of 0.25% of phosphorus from dicalcium phosphate can contribute 20 mg·kg-1 or more F- to the diet (McDowell, 1992). Thus, commercial diets for nonhuman primates, under some circumstances, can have substantially higher F- concentrations than found in human diets.

F- has been shown to have a cariostatic effect in monkeys. Cynomolgus monkeys (Macaca fascicularis) 11-13 months old were given drinking water containing F- at 2 ppm for 5 years, beginning before eruption of their first permanent molars (Cohen and Bowan, 1966). The F- concentration of the diet was thought to be low but was not measured. The diet was composed of an offering of bread, bananas, canned carrots, biscuits, peanut butter, boiled eggs, jam, complan, dates, marmie, and cheese (Cohen and Bowan, 1966). Animals receiving F- had less caries than animals not receiving F-. The F- was more effective if teeth were being formed while exposed to F- than if they were exposed after mineralization (Bowen, 1973). Those results are in contrast with the observations of Ockerse and de Jager (1957), who added F- at 10 mg·kg-1 to the drinking water of African green monkeys (Cercopithecus aethiops) of unstated age that were fed a cariogenic diet; the added F- had no effect on the incidence of caries.

An adequate F- intake by men was recently estimated to be 4 mg·d-1 (Institute of Medicine, 1997). Assuming that average daily intake of food is 500 g of DM, that is equivalent to F- at 8 mg·kg-1 of dietary DM. However, F- needs of people of all ages seem to be best met by its inclusion in drinking water at 1.0-2.0 mg·L-1.

Some signs of mild fluorosis (mottling of the teeth) are seen when water contains F- at 2 mg·L-1.

REFERENCES

Alley, M.C., E.K. Killam, and G.L. Fisher. 1981. The influence of D-penicillamine treatment upon seizure activity and trace metal status in the Senegalese baboon, Papio papio. J. Pharmacol. Exp. Therap. 217:138-146.

American Feed Control Officials. 1997. Official Publication, Association of American Feed Control Officials. Atlanta, GA: Association of American Feed Control Officials.

Amine, E.E., L.M. Ausman, D.M. Hegsted, and S.N. Gershoff. 1972. Iron deficiency and absorption in infant squirrel monkeys. Fed. Proc. 31:711.



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