Because foods vary greatly in their water content, dry weights are more useful indicators of nutrient intake than wet weights and allow more accurate comparisons among studies. Daily dry-matter intakes can be calculated by multiplying the grams of dry matter consumed per hour or per feeding bout by the hours or feeding bouts per day. That yields a good estimate of total dry matter consumed. If the time spent in eating is clearly separated from foraging time, the total time spent in feeding on a given food and the total dry matter taken in from eating that food tend to lead to the same answer (Knott, 1999).
Total dry matter consumed, however, is still not the best method for evaluating usable energy and nutrient intake, because losses during digestion are not considered. Ideally, the diet should be analyzed for fiber components, partly or mostly indigestible fractions of dry matter, depending on the consuming species (see Chapter 3, “Carbohydrates and Fiber”). If laboratory support is available, data on gross energy and nutrient concentrations in natural foods are additional useful measures. However, gathering such data is extremely time-consuming, expensive, and in some field situations almost impossible. For many small, fast-moving, and unhabituated arboreal primates, it is extremely difficult to collect all the needed bits of information. The percentage of time spent in feeding on particluar items is often as good a measure as is realistically possible to determine.
The designation of the different feeding strategies (folivory, frugivory, insectivory, and gummivory) is based on the food category with the highest percentage of use (Chapman, 1987). Seasonal differences can make a normally frugivorous species appear folivorous and vice versa (Chapman and Chapman, 1990). Many primates exploit a small number of plant species heavily but sample small amounts of many species (Hladik et al., 1971; Glander, 1975; Smith, 1977; Chapman, 1988). Insectivory and gummivory are two feeding strategies predominantly of very small primates. Tarsius are small and can survive by eating only insects. Saimiri (the second commonest experimental primate but not well studied in the wild) is the smallest cebid and the most insectivorous. Some prosimians and most Callithrix, are small and can survive by eating mostly gums. The cercopithecines have been separated into two groups, colobine (Table 1-4) and noncolobine (Table 1-5). All colobines are foregut fermenters and are folivorous or granivorous (seed-eating). The noncolobine cercopithicines are hindgut fermenters and are generally more omnivorous.
Considering the different methods and circumstances under which feeding-ecology data are collected, the information gathered will be variable in quality and subject to potential errors. The various data collection systems are described in this chapter, and the reader is urged to identify the system used in gathering the data of interest and to use personal judgement in interpretation of their applicability. Feeding-ecology data can be used to evaluate the appropriateness of a captive diet but do not provide a basis for setting quantitative nutrient requirements. They are used to classify primate species as primarily granivorous, folivorous, omnivorous, gummivorous, or insectivorous and provide guidance to food preferences and to probable qualitative and roughly quantitative nutrient needs. For example, leaves are generally higher in protein (dry basis) than are fruit, although wild fruits are much higher in protein than are fruits cultivated for human use (Conklin-Brittain et al., 1998, 1999, 2002). Consequently, folivores generally consume a diet higher in protein than do frugivores. An even more important consideration might be the presence of physical factors, such as fiber, in the natural foods of folivores and the effects these factors have on digestive function and health. Thus, evidence from feeding ecology studies and controlled research with captive primates has been used to develop the proposed dietary fiber concentrations shown in Chapter 3.
Many primate species consume diversified, omnivorous diets. Most of the primates that are routinely used in research fall into this category, in part because their diverse and omnivorous diet seems to make them more adaptable, and they are easier to keep in captivity than are more specialized species. For species that are rarely kept successfully in captivity, a close examination of their feeding ecology may be helpful in formulating a diet that is most appropriate for them. The folivorous monkeys pose a particular problem, and only recently have research trials begun to identify those combinations of formulated complete diets and cultivated foods that can substitute for their normal wild diet.
The primary function of the digestive system is to extract energy and essential nutrients from an animal’s environment in support of metabolic processes. Performing that function requires a series of physical and chemical steps that are related to the anatomy of the digestive system. The primary significance of gut structure is related to its effect on food selection and processing (Clemens and Phillips, 1980). Specialized structures are involved in food acquisition, ingestion, maceration, deglutition, and digestion. Secretions from the salivary glands, stomach, pancreas, liver, and intestinal tract provide lubrication and enzymes in a watery medium with a pH that is optimal for digestion. Symbiotic microorganisms in the foregut or hindgut of some animals provide energy and nutrients by degrading structural carbohydrates that are unaffected by endogenous enzymes and by synthesizing amino acids and