aOnly aged adults of these species appear to be at risk.
being formulated for artificial rearing. In reality, some nutrients appear to be present in breast milk at concentrations higher than required. Thus, such estimates can provide margins of safety for nutrients that are poorly absorbed from synthetic milk and ensure that milk replacers will be nutritionally complete.
Milk volumes ingested by mother-reared infant primates are difficult to measure, and few data have been published (Oftedal, 1984). The commonly used weigh-suckle-weigh method, in which an infant is weighed before and after each nursing bout during a 24-hour (or longer) period, is not particularly applicable to primates, because an infant primate nurses often and might hold the nipple in its mouth when not nursing. As a consequence, it is difficult to determine when nursing starts and stops. Other methods for measuring milk consumption, such as the use of isotope dilution, have been used little with nonhuman primates, although Buss and Voss (1971) used such a technique with baboons (Papio cynocephalus).
Formula intakes by artificially reared infants can be determined with reasonable accuracy by measuring volumes consumed over a long period (to modulate diurnal variations). Caution is urged because large holes in artificial nipples and the manipulative skills of young primates often lead to substantial losses of formula and overestimates of intake. If formula spillage is observed and ‘‘nonspillers’’ are selected for study, reliability of intake data can be enhanced. Caloric density of the formula must be taken into account because it will affect volumes of milk ingested. Some early researchers concluded that neonates of several species are incapable of handling nursing bottles and should be hand-fed at frequent intervals up to the age of 30-60 days. Other studies have found that newborn infants adapt quickly to the bottle and will self-feed soon after birth.
COMPOSITION OF MOTHER’S MILK
There are several reports on the gross nutrient composition of milk of nonhuman primate species (Van Wagenen et al., 1941; Pilson and Cooper, 1967;Buss 1968a, b, 1975; Buss and Cooper, 1970, 1972; Taylor and Tomkinson, 1975; Buss et al., 1976; Nishikawa et al., 1976; Turton et al., 1978; Lonnerdal et al., 1984) (Table 9-4). Many of the reports were published years ago, and some of the analytic methods are different from those of today. In some cases, the method of milk collection was such that samples obtained were not representative of milk consumed during a complete nursing bout; thus, a sampling bias was introduced (Oftedal, 1984). For example, fat concentrations in milk at the beginning of mammary evacuation can be one-third or less of concentrations near the end of mammary evacuation (Erb et al., 1977). Ideally, milk sampling replicates normal suckling behavior. It should include the normal interval for accumulation of milk before suckling and the normal amount of milk removed by suckling. If milk samples represent less than normal expression of the contents of the mammary gland, concentrations of fat and other nutrients can be in error.
The stage of lactation also affects milk composition. As lactation progresses and infants are weaned, the volumes of milk produced per nursing bout decrease, and concentrations of fat and protein dramatically increase. Maternal diet can also affect some composition values if nursing mothers have been fed diets that are not nutritionally complete. Finally, excessively vigorous manual milking can result in bleeding that is insufficient to color the milk noticeably but sufficient to affect its composition. Various milking devices have been developed to obtain milk samples without causing trauma to the breast (Buss and Kriewaldt, 1968). Ketamine as a sedative and oxytocin to promote milk ejection have been helpful in the collection of milk samples and appeared to have no effect on milk composition (Buss, 1968b), but nonphysiologic doses and repeated injections of oxytocin might result in spurious values (Oftedal, 1984).
There are reports on specific components of nonhuman-primate milk, including individual milk proteins (Davidson and Lonnerdal, 1986; Kunz and Lonnerdal, 1994), amino acids (Hayes et al., 1980; Buss and Cooper, 1970), oligosaccharides, triglycerides (Turton et al., 1978; Myher et al., 1994; Buss et al., 1976), cholesterol (Mott et al., 1982, 1985, 1990, 1993a,b), and minerals (Lonnerdal, 1984; Buss et al., 1976; Turton et al., 1978; Buss and Cooper, 1970). In chapter 5, detailed information about fatty acid composition of milk from different primates, and the effect of fat thereon, is provided. In many cases, the information was sought to explore the applicability of nonhuman primates as models for study of issues in human pediatric nutrition.
Nutrient Intakes with Milk Replacers
Nutrient intakes by artificially reared infants can be estimated by multiplying the volume of milk replacer ingested by the concentration of nutrients in the formula. Estimates of nutrient intake in commercial products will be more accurate if the milk replacer is analyzed, as opposed to