too small can restrict growth and movement enough to produce noticeable muscle atrophy (Faucheaux et al., 1978). That effect can be a reflection both of limited exercise and an associated lower energy need, which lead to lower food consumption and inadequate protein intake by young primates from low-protein, high-energy diets.

Substrates used on enclosure floors are manipulable items, can provide comfort, and can be part of foraging enrichment (Westergaard and Munkenbeck-Fragaszy, 1985; Bayne et al., 1992; Byrne and Suomi, 1995). Straw, hay, wood-wool, shredded paper, wood chips, blankets, corncobs, and soil have been used. Species or individual animals can show preferences for and more effective use of some substrates than others (Ludes and Anderson, 1996). It is, however, important that gastrointestinal disorders caused by ingestion of substrate or of pathogens in substrate be minimized by care in selecting, storing, and manipulating these materials (Baer, 1998).

Wild Environment versus Captivity

In the wild, primate diets are diverse and include leaves, stems, flowers, fruits, seeds, gums, insects, spiders, lizards, eggs, and other animal matter. The items selected vary with the species, and the proportions selected can vary from month to month without a clear association of the selections with seasonality of the habitat (Chapman and Chapman, 1990). Precisely gathered information on natural dietary habits is scarce, and field studies that include quantitative nutrient-intake data are exceedingly rare. Data gathered at different sites over time to account for location and seasonal differences and in which food use has been quantified and food composition determined can provide guidance for the development of rational captive dietary systems.

To succeed in the wild, primates must learn by example to select foods that, in toto, provide nutrient requirements and that are not toxic. Acquisition of nutrient needs requires that wild primates spend 25—90% of their waking hours in foraging for and consuming food (Clutton-Brock and Harvey, 1977).

In contrast, conventionally fed primates in captivity can fulfill their nutrient and energy needs in just a few minutes. Thus, successful enrichment programs involving food are usually designed to extend foraging time by requiring primates to ‘‘work’’ for food and to spend more time in food processing. Nutritionally complete extrusions can be placed in covered plastic buckets and suspended by ropes from structures in primate enclosures. Primates can jump onto the buckets or slide down the ropes and reach through holes in the buckets to acquire food. Buckets with smaller holes allow access by small primates while ensuring that larger, dominant animals will not take more than their share. In this instance, environmental enhancement is accomplished through the means of providing the standard diet rather than through addition of treats that might be nutritionally incomplete.

Novel foods are often presented in the form of treats, although predictable presentations of treats are soon no longer novel. Treat feeding, in which the treat is handed to the primate, can foster trust and bonding with the care-taker and provide short-term sensory stimulation, but it differs greatly from natural foraging in occuping so little time (Fajzi et al., 1989). Furthermore, evidence of nutritional wisdom among nonhuman primates is not convincing. It is obvious that free-living primates have successfully evolved with their wild food supply and have learned which foods to choose and which to avoid. But there is ample evidence that captive primates given a selection of cultivated foods or treats of various nutrient densities do not consistently choose a complete diet (Ullrey, 1989; Oftedal and Allen, 1996). It also should be noted that the botanic classification of wild foods into categories, such as fruit, has commonly led to the misuse of cultivated fruits (for example, bananas, oranges, and apples) as though they were comparable with their wild equivalents in nutrient composition, color, texture, and proportions of inedible husks or shells. In fact, wild plants and their various parts are quite different from the cultivated plants used for human food (Edwards et al., 1990a, 1990b; Oftedal and Allen, 1996). In particular, wild foods tend to be higher in fiber, and that fiber is often of low digestibility. Nutrient bioavailability also varies with source (Ammerman et al., 1995) and can be different between wild foods and cultivated foods.

Nearly all captive primate species should be provided a nutritionally balanced dry food as the predominant item in their daily ration. If it is appropriately formulated, it will have a positive effect on oral health, and the addition of particular vegetables or fruits will not seriously distort nutrient balance until their proportion approaches 50% on a wet basis (Edwards, 1997). The main reasons for this are that such items as green beans, celery, carrots, and kale are all good sources of many nutrients and that they are also high in water (88–94%). Thus, even though they might make up a high proportion of dietary wet weight, they have a relatively small influence on the balance of nutrients supplied by pellets or extrusions that are typically 5–13% water.

However, if high-moisture vegetables or fruits are fed with a nutritionally balanced food that is high in moisture (canned or gel products) and the primates being fed are as small as marmosets and tamarins, it might be difficult for them to consume sufficient dry matter to meet nutrient and energy needs (Barnard et al., 1988).

If dry, very palatable foods that are nutritionally incomplete are offered, as is the case with many seeds and nuts (Ullrey et al., 1991), these preferred items might be con-

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