No. According to the NIH OACU Guidelines for Use of Non-Pharmaceutical-Grade Chemicals/Compounds in Laboratory Animals (2008), the vehicle used to facilitate administration of a compound is as important of a consideration as the active compound in the preparation. Diet as a vehicle, either whole or as the sum of its parts, would not meet the standard for pharmaceutical grade as defined by this document.
You may have been asked this question by your IACUC due to a passage in the 8th edition of the Guide for the Care and Use of Laboratory Animals (2011) stating that pharmaceutical-grade chemicals and other substances should be used, when available, for all animal-related procedures (page 31). In general, deviations from “Must” or “Should” statements within the Guide require justification and approval by your institutional IACUC.
Alternative dosing techniques (gavage, injection) can introduce stress from handling and increase the risk for potential injury. Stress can affect animal well-being as well as scientific parameters through modifications in behavior and physiology. Dosing via diet is an established method for delivering test compounds to animals that is non-invasive, reducing stress and potential injury from handling. Therefore, use of non-pharmaceutical grade compounds as a delivery method is justified, as it is advantageous for both animal welfare and experimental design.
Guide for the Care and Use of Laboratory Animals: 8th Edition (2011). National Research Council Committee for the Update of the Guide for the Care and Use of Laboratory Animals.
Guidelines for the Use of Non-Pharmaceutical-Grade Chemicals/Compounds in Laboratory Animals. (2008). Animal Research Advisory Committee, Office of Animal Care and Use, NIH.
Laboratory routines cause animal stress. (2004). Balcombe, J.P., Barnard, N.D., and Sandusky, C. Contemp Top Lab Anim Sci 43, 42-51.