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The Problem of Age Estimation and Skeletal Age

During the last four decades, nonhuman primates have been used increasingly in various fields of biomedical research. They are now indispensable in many areas, such as reproduction, developmental biology, teratology, etc. Close phylogenetic, as well as ontogenetic similarities to man, make nonhuman primates very essential, first-choice animal models in many investigations. Animals born and captured in the wild and of unknown age, or randommated in free-ranging colonies (as opposed to those which are purpose-bred for research and born in breeding colonies) are still the most frequently used. The estimation of the chronological age in these animals is generally somewhat arbitrary and is based on the body weight or dental age standards of young animals. Many factors can contribute to the wide variation in body weight of nonhuman primates. These include the quantity and quality ofmilk produced by and diet fed to the mother, environment stresses in the colony during lactation, temporary illness leading to anorexia, and individual feeding habits of the neonate. Thus, body weight is not an accurate method to use for critical age assessment, particularly in young animals. It may, however, be of value in placing monkeys in broad age categories if their previous histories are known. Body weights of colony-born, mother-reared neonates will differ from those of colony-born, nursery-reared neonates, since conditions are better controlled in the latter instance [40, 44, 51]. The dental age, expressed by the sequence of eruption of the deciduous