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For those of you who are breeding/using CD1s, I am curious to know whether yours are food crunchers'''''? If so, how are you managing it? Have you found that a change of diet (cellulose/fat %), seeds, sticks, nesting, or any other environmental enrichment made a significant difference?
There are a couple of suggestions that might help:
One is that softer diets are more likely to be 'crunched' than harder ones - and also the more 'highly-strung' strains of mice do this more frequently.
Secondly, there's a theory that mice are just carrying out their natural feeding behaviours when they dissect the pellets - mice are granivorous and would naturally husk seeds and grains in search of the tasty inside parts. When we think that they are annoyingly 'crunching' the diet, from the mouse's point of view, they are shredding the pellet in hopes of finding a tasty something inside.
Therefore, providing whole seeds can allow mice to express this behaviour and thus reduce their focus on the hopper. It also allows the opportunity for mice to express foraging behaviour. Advice is to provide small seeds, such as millet, chia, linseed, sesame, etc, rather than sunflower seeds, as the latter can result in rather fat mice!
We've tried this for some 'crunching' mice and (anecdotally) it did seem to help the problem. We used human food-grade seeds, so that it was acceptable for use within the unit.
There's more about it in this paper: Can seeds help mice with the daily grind? June 2013, Laboratory Animals 47(4), DOI: 10.1177/0023677213491403
Somewhere down the line I have absorbed that food crunching is a form of stereotypic behaviour that is related to weaning at a point where the newly weaned mouse struggles to obtain sufficient food from the diet in the hopper so the behaviour develops as a response to the hunger experienced (I can't find a paper backing this up).
Our techs here either delay weaning until they think the young are large enough to feed adequately or provide some in-cage powdered diet (the remnants from the bottom of the bag of diet are saved for this purpose) when weaning smaller mice, so they don't go hungry. They feel this works but we have no hard data to say our incidence of crunching is less than anywhere else.