Hoarding behavior in obese and control rats: evidence indicating cost differences.

Hoarding behavior of rats can be described by the equation y = ax + b, where y is the amount of food hoarded, x the rat's body weight, a the negative slope of the regression line, and b, the ordinate at zero abscissa. We repeatedly evaluated the parameters of this equation in six obese Zucker rats and six controls, from 8 to 32 weeks of age. The mean slope of the regression lines remained close to -11 in both groups of rats, until 24 weeks of age. From then on, the slopes of the obese rats decreased dramatically to c. -3, and remained as such for the rest of the experiment, while that of controls remained constant. At this age (24 weeks), controls weighed 453 +/- 14 g and obese rats 729 +/- 18 g. We suggest that the decreased slope of hoarding in obese rats was due to an increased cost of the hoarding behavior.