returned to normal. Thus, it would appear that a Mg concentration of 0.04% in dietary DMshould support maintenance requirements when dietary calcium and phosphorus concentrations are relatively low. However, few studies of Mg requirements of nonhuman primates have been reported, and higher dietary concentrations of calcium and phosphorus have been shown to elevate the Mg requirements of some other species (Underwood and Suttle, 1999). Examination of natural-ingredient diets for primates and other mammals, with their higher Ca and P concentrations, indicates that 0.08% Mg is more likely to be a consistently adequate dietary level. Thus, the recommendation in Table 11-2 reflects a presumed adequate dietary level of 0.08%, whereas the estimates of 0.04 to 0.074% Mg in Table 11-1 are minimum requirements.

Mg concentrations in the milk of rhesus monkeys are 32.9 ± 3 µg·ml-1 compared with 49.6 ± 12.1 µg·ml-1 in colostrum (Lonnerdal, et al., 1984). Formulas for artificial rearing should contain supplemental sources of this essential nutrient.

Potassium

Potassium (K) is usually found in high concentrations in plant and animal tissue. Concentrations over 3% are typical in plant DM, and deficiencies are rare. K helps to regulate tissue turgidity of plants; in animals, K is the major intracellular cation and is largely responsible, with sodium and chloride, for the maintenance of osmotic pressure and acid-base balance. A K concentration of 0.24-1.1% in dietary DMappeared to support maintenance in baboons (Hummer, 1970). However, studies with other species using natural-ingredient diets suggest that minimum K requirements may be 0.4% or more of dietary DM, and may depend upon species, life stage, and diet composition (Underwood and Suttle, 1999). Thus, recommendations in Table 11-2 reflect the higher concentrations reported to be adequate with natural-ingredient diets. In rhesus monkeys, Lonnerdal et al. (1984) found that K is higher in colostrum (367 µg·ml-1) than in milk expressed after 30 days of lactation (260 µg·ml-1).

Sodium

The major extracellular cation in mammals is sodium (Na). Thirst and total body water are regulated by dietary Na. Na thirst has been identified in a number of mammal species. Natural diets usually contain adequate supplies of Na, although strict herbivores might be at risk for Na deficiency. Depending on soil and environmental characteristics, plants might be poor sources of Na or phosphorus. The influence of Na on blood pressure has been extensively studied in primates because of the high incidence of hypertension in Western human populations. Increasing dietary sodium chloride (NaCl) concentrations to 3-6% increased systolic and diastolic blood pressure in African green monkeys, spider monkeys, and hamadryas baboons. Rhesus monkeys, however, failed to show an increase in blood pressure under the same conditions over a 6-week period (Srinivasan et al., 1980, 1984). The rhesus monkeys expressed a distaste for the high-NaCl diet, and a decline in body weight was associated with increasing dietary NaCl.

Diets containing 0.25-0.65% Na appear to support maintenance of nonhuman primates, but are likely to exceed minimum needs (Hummer et al., 1970; National Research Council, 1978). The milk of rhesus monkeys contains Na at about 171 µg·ml-1 in the first week of lactation, but milk Na appears to decline to about 90 µg·ml-1 after a month (Lonnerdal et al., 1984). Apparently female rhesus monkeys ingest more NaCl than do males when presented the opportunity (Shulkin, 1992). However, ovarian hormones do not appear to be involved in this sex difference (Krecek et al., 1972; Krecek, 1973).

Chloride

The major digestive chemical in gastric secretions is hydrochloric acid. With the exception of foregut-fermenting primates, the acid stomach is the first and the major organ responsible for processing feedstuffs. Chloride (Cl) is also critical (with sodium and potassium) in the osmotic regulation of cells and tissues. Hummer (1970) fed diets containing 0.27-0.62% Cl to baboons, and they appeared to support maintenance but probably exceeded minimum requirements. The lower of the previous National Research Council (1978) recommendations of 0.2-0.55% dietary Cl would be expected to be sufficient, based on comparisons with the Cl requirements of other species.

Sulfur

Important compounds in the diets of primates that contain sulfur (S) include biotin, thiamin, cystine, cysteine, methionine, and taurine. A frank deficiency of S in primates has not been described, although taurine deficiency may occur in neonates (Hayes, 1980). Excessive intakes of protein high in S-containing amino acids (cystine, methionine, and taurine) might exacerbate problems of renal calcium loss.

TRACE MINERALS

Iron

Iron (Fe) is an essential component of such proteins as hemoglobin, myoglobin, and ferritin; and some enzymes require Fe as a cofactor (Fairbanks, 1999). Iron in heme



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