Diet Replenishment for Ad-Libitum-Fed Mice Housed in Social Groups is Compatible with Shelf Life

Dear Editor,

In the May 2008 issue, the report by Huerkamp and Dowdy¹ suggests that mice fed free choice would consume feed in wire-lid hoppers well before the expiration date of the feed. Their main objective was to determine if their “topping off” method of food replenishment would result in feed consumption prior to its shelf life expiration. We commend the authors for addressing this important issue; however, the study design addressed a single method of feed replenishment and could be misleading to some readers.

In this report, the feed from the wire-lid hopper was weighed, replaced and subsequently “topped off” with fresh feed. This procedure modeled the protocol used at the authors’ institution where the wire-lid hopper may be changed only once every 6 mo and the feed topped off weekly. However, there are institutions where the wire-lid hopper is replaced every 2 wk. On weeks when the wire-lid hopper is not changed, it may be “topped off” with fresh feed. The following week when a clean wire-lid hopper is provided, the remaining feed is transferred to the new wire-lid hopper before “topping off.” Over time this results in a mixture of feed of various ages. The feed at the top of the wire-lid hopper is the freshest, the feed at the bottom of the hopper is principally the feed provided the previous week, and the middle layer is a mix of feed of various ages.

We have provided color-dyed medicated feed to mice using the husbandry procedures described above. At the end of the medicated feeding period, undyed feed was provided. The medicated feed was not discarded but rather was “topped off” as described above with undyed feed. This provided us the opportunity to assess feed consumption over time. Six months after the last batch of dyed feed was provided, we still found dyed pellets in a considerable number of cages. Thus, with this method of “topping off,” animals may ingest feed beyond the 180 d expiration.

We recognize that mice may have had a preferential taste for undyed feed when given the choice. Further investigation is needed to determine whether this alternative husbandry procedure could result in provision of expired feed.

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Sincerely,

Rodolfo J Ricart Arbona, MLAS, DVM
Research Fellow, Memorial Sloan-Kettering Cancer Center, Weill Cornell Medical College, and The Rockefeller University
Neil Lipman, VMD
Director, Research Animal Resource Center, Memorial Sloan Kettering Cancer Center and Weill Medical College of Cornell University
Felix Wolf, DVM, Ph.D.
Deputy Director Research Animal Resources Center, Memorial Sloan-Kettering Cancer Center and Weill Cornell Medical College