Open- and closed-formula laboratory animal diets and their importance to research

Abstract

Almost 40 y ago the scientific community was taking actions to control environmental factors that contribute to variation in the responses of laboratory animals to scientific manipulation. Laboratory animal diet was recognized as an important variable. During the 1970s, the American Institute of Nutrition, National Academy of Science, Institute of Laboratory Animal Resources, and Laboratory Animals Centre Diets Advisory Committee supported the use of 'standard reference diets' in biomedical research as a means to improve the ability to replicate research. As a result the AIN76 purified diet was formulated. During this same time, the laboratory animal nutritionist at the NIH was formulating open-formula, natural-ingredient diets to meet the need for standardized laboratory animal diets. Since the development of open-formula diets, fixed-formula and constant-nutrient-concentration closed-formula laboratory animal natural ingredient diets have been introduced to help reduce the potential variation diet can cause in research.

Figure 1.

The effect of batch-to-batch variation in the total daidzein + genistein (D + G) content in batches of the same diet (PMI 5002) with different mill dates on the timing of vaginal opening in F344 rats. The total daidzein + genistein content can vary 3-fold depending on mill date, producing significant (P < 0.05) differences in the time of vaginal opening between different mill dates at postnatal days (PND) 34 and 36. The low-phytoestrogen diet in the chart is PMI 5K96. Diamond, PMI 5K96 control (D + G = 7 µg/g); square, PMI 5002 with mill date of 2003 Aug 20 (D + G = 98 µg/g); triangle, PMI 5002 with mill date of 2004 Nov 07 (D + G = 223 µg/g); circle, PMI 5002 with mill date of 1997 Jul 23 (D + G = 431 µg/g). This figure is based on that in reference 32 and appears with permission.