bly not a problem in nursing wild primates. In humans, if infant formula thickened with an indigestible carbohydrate, such as locust bean gum, replaces mother’s milk, Ca availability is reduced compared with that in unthickened infant formula or formula thickened with a digestible carbohydrate, such as pregelatinized rice starch (Bosscher et al., 2000). Further, it has been shown that the Ca in fortified soy milk is absorbed at only 75% of the efficiency of Ca in cow’s milk (Heaney et al., 2000).

Tarsiers held at the National Zoological Park were fed crickets exclusively, a particularly poor calcium source (see Chapter 12). Repeated breeding failures were experienced until a high-Ca (8%) cricket diet was made available to the free-ranging crickets in the tarsier enclosure (Roberts and Kohn, 1993). Although the Ca concentrations in cricket tissues were unchanged, the residue of high-Ca diet in the cricket gut supplied sufficient Ca to meet tarsier needs. Successful births and weanings were observed regularly after that dietary change was made.

Mineral mixes (salt mixes) historically used in diets for laboratory primates appear to have provided about 0.2% of available (non-phytate) P in the diet. When they were combined with the P in food ingredients (those furnishing protein tending to be richer in P), available P concentrations (air-dry basis) in formulated diets were about 0.3-0.4% and appeared to be adequate (National Research Council, 1978). When the lowest National Research Council (1978) value is expressed on a DMbasis, the estimated dietary available P requirement would be 0.33% (assuming 10% moisture in the air-dry diet). Total P requirements in natural-ingredient diets are generally higher because the bioavailability of P tends to be less than that in inorganic P sources, particularly when associated with phytate in commonly used cereals and oil-seed meals. P bioavailability studies have not been conducted with nonhuman primates, but P bioavailability values have been reported for feed ingredients fed to pigs (National Research Council, 1998). Phytate P is believed to be only slightly available or totally unavailable to non-ruminants. In ruminants, the phytase activity of ruminal microorganisms renders nearly all of the phytate P available for absorption (National Research Council, 2001). Whether this would be true for microorganisms in the complex stomach of the Colobinae has not been established.

Provision of a dietary Ca:P ratio between 1:1 and 2:1 has been emphasized in setting Ca and P requirements in the past. However, it has been shown in the pig that inorganic P, added to the diet to maintain a particular Ca:P ratio, will lower use of phytate P, and phytate lowers use of Ca (Underwood and Suttle, 1999). Furthermore, excess Ca lowers P absorption (National Research Council, 1998). Thus, it might be important to consider the Ca and P concentrations in diets used in defining Ca and P requirements and the effects of phytate on requirement estimates.

In practical diet formulations for nonhuman primates, the addition of stable phytases might increase phytate P availability, on the basis of studies with other species (Cromwell et al., 1995). However, the choice of phytase, and its resistance to the heat and pressure of food processing, will influence its effectiveness (National Research Council, 1998).

Magnesium

It has been said that about 70% of the body’s magnesium (Mg) of ruminants is in the skeleton (Todd, 1969), although Shils (1999) has stated that bone contains about 53% of the Mg in the adult human body. Mg is a component of regulatory enzymes and enzyme systems, and over 300 essential metabolic reactions involving Mg have been identified (Shils, 1999). Mg helps to regulate muscle and nerve function and influences the metabolism of protein, carbohydrate, fat, and nucleic acids. ATP exists in all cells primarily as MgATP, and the complex plays a central role in many of these reactions. Cyclic adenosine monophosphate (cAMP), formed from MgATP and adenylate cyclase, is involved in the secretion of parathyroid hormone (PTH), and PTH exerts some of its physiologic effects through the formation and actions of cAMP. That role of Mg might partially explain the hypocalcemia seen in Mg-depleted rhesus monkeys, humans, calves, sheep, dogs, and pigs (Dunn, 1971).

Studies of the effects of dietary calcium, phosphorus, or vitamin D on absorption and retention of Mg in humans have produced equivocal results (Shils, 1999). Long-term balance studies with healthy adults generally suggest that increased calcium intakes do not substantially influence Mg absorption or retention. Some reports indicated that high phosphorus intakes decreased Mg absorption, whereas others did not. Some patients, but not others, with impaired calcium absorption and both osteomalacia and osteoporosis showed improvement in Mg absorption when given vitamin D or calcitriol orally. Increased intakes of Mg have been associated with decreased calcium absorption or no effect.

Signs of Mg depletion in humans include neuromuscular, gastrointestinal, and cardiovascular changes (Shils, 1999). Tremor and muscle fasciculations are seen; anorexia, nausea, and vomiting can be experienced; and in severe Mg depletion, there can be electrocardiographic changes compatible with hypokalemia or hypocalcemia.

In only 4 weeks, rhesus monkeys fed a diet containing Mg at 3 mg·100 g-1 (0.003%, air-dry basis) (Dunn, 1971) exhibited hyperirritability associated with hypomagnesemia, whereas monkeys fed a control diet containing Mg at 102 mg·100 g-1 (0.1%, air-dry basis) did not. Affected macaques fed additional Mg (33% of control concentrations, equivalent to 0.034% of the diet on an air-dry basis)



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