Diet restriction in rat toxicity studies: Automated gravimetric dispensingequipment for allocating daily rations of powdered rodent diet into pouches and 7-day feeders

Survival of ad libitum-fed rats has declined in the 2-year carcinogenicity bioassay. Restriction of the number of calories, without compromise of the overall nutrition offered to animals including rats, results in increased l ifespan of animals. Diet restriction in rats is best achieved through offer ing of rations of feed daily instead of weekly, as is routinely done in ad libitum studies. The objective of this project was to develop an accurate a nd precise method of dispensing daily rations of feed. A gravimetric vibrat ory-type dispenser was used to dispense target weights of 15 and 20 g of po wdered certified rodent diet into either labeled pouches or seven-well caro usel feeders. The tolerance of the dispenser was the target weight 3%. The amount of food offered to the diet-restricted rats was approximately 25% lo wer than that consumed by rats offered diet ad libitum. After 2 years, male rats offered 20 g and female rats offered 15 g of powdered rodent diet dai ly had remarkably lower body weights than did animals offered the diet ad l ibitum. Generally, the rats ate the entire ration of food offered to them e ach day. Survival of the diet-restricted rats was 70% to 82% at the end of a 2-year study. This investigation demonstrates that modest reduction of fo od intake, resulting in increased survival of Sprague Dawley rats in 2-year carcinogenicity bioassays, can be achieved reliably and efficiently throug h use of an accurate and precise automated method of dispensing powdered di et for use in multiple rat studies. In addition, this method of food dispen sing provides a practical way to administer test compound in the diet under the conditions of diet restriction.