Obesity is a global problem and the percentage of individuals who are overweight or obese is increasing in line with dietary changes and decreased amounts of physical activity. The causes and mechanisms of obesity need to be better defined and thus increased biomedical research of obesity is needed as well as the development of animal models that closely mimic human physiology and anatomy1.
Monkeys are appropriate animal model of obesity not only because of their anatomical, physiological and genetic similarities to humans but their size and long life span allow for longer sampling periods. It was observed that body mass index in long-tailed monkeys can influence expression of obesity-related genes2. In addition to genetic influences, the environment can also affect obesity.
Phenotype is manifested through the expression of genes that result in specific qualitative and quantitative characteristics of animals that can be seen and measured. Phenotypes related to body measurements are useful for quickly identifying obesity-related characteristics. Currently, there is limited information regarding the physical characteristics or phenotype of obese monkeys, which has presented as an obstacle for classifying obese and non-obese animals.
Presently, the criteria for obesity in primate species are still based on those for humans. In this context, a new study aimed to obtain information on body dimensions that play a role in determining quantitative indicators of obesity in primates and how they can be applied to an animal model of obesity3.
For study purpose, fifteen adult male Long-Tailed Monkeys (LTM) were divided into three groups of five that received one of three diets: Diet A: A commercial monkey chow diet, Diet B: Monkey chow supplemented with egg yolk and Diet C: In which wheat was the main ingredient and beef tallow was added. Body measurements, including body weight, were collected monthly.
The monkeys consumed varying amounts of the different diets with animals fed Diet B having the highest average daily consumption rate and Diet A the lowest. Those monkeys that received Diet B (chow+egg yolk) had the highest amount of weight gain and LTM fed Diet A (monkey chow) had the lowest, the differences were significant. The LTM-fed monkey chow (Diet A) and the obese diet (Diet C) had slight differences in overall weight gain but these differences were not significant.
All phenotype variables were positively correlated with each other. Analysis of these correlations, in which body weight was positively correlated to abdominal skinfold thickness and the thickness of folds on the skin on the back, hind legs, forelimbs, soles of the feet and palms, as well as the circumference of the back, waist, chest, arm, foot, thigh, calf and head.
It was concluded that monkeys fed an obese diet containing egg yolk had a greater tendency to develop obesity. Waist circumference, hip circumference and abdominal skinfold thickness can be qualitatively used as indicators of an obese phenotype in monkeys.
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