Effects of unpalatable diets and food restriction on feed efficiency in growing rats

During a 15-day experiment, weanling rats fed a 10% casein diet adulterated daily by one of four aversive taste stimuli ate 12–16% less than their controls fed ad lib on the unadulterated diet. They also demonstrated an inhibition in feed efficiency (g body weight gain/g food intake) during the first 8 days. A second control group, pair-fed to the group receiving the adulterated diet, also showed a reduction in feed efficiency. By Day 9, a compensatory process was evident in the rats fed the unpalatable diet such that feed efficiency increased above that observed for the ad lib control group. By the end of the experiment all three groups exhibited the same efficiency. The ratio of urinary nitrogen to total nitrogen intake was higher in rats fed the unpalatable diet ad lib compared to those offered the unadulterated diet ad lib. This observation suggests that the rats on the unpalatable diet were using more of the dietary protein as a caloric source than were their controls.