ABSTRACT
Some species store bile from the liver in the gallbladder (humans, swine, cattle, sheep, chickens), whereas others (rats, horses, deer, elk, moose, camels) have no reservoir to store bile, and this in turn may affect lipid digestion. Another species difference is in nitrogen utilization. For example, mammals excrete excess nitrogen resulting from protein metabolism as urea, whereas birds excrete uric acid. Many different species of animals have been used extensively as research models to obtain data on the nutrient requirements of humans, and to learn the mode of action of various dietary additives. The researcher must be aware of differences in the nutritional requirements of different species, or erroneous conclusions could be drawn. For example, vitamin C is required for humans, guinea pigs, and monkeys but not for swine and rats, which are frequently used as animal models.
