You don't have to add anything I have been using this for 7 to 8 years straight without issue and observed proper weight gain, you can't push animals and it's about having the right animal, from what I gathered from your previous post your colony is not strong as it should be and if it was me I would start from scratch.
A good rat colony need to be build on solid foundation, health issues that need to be treated or addressed should be addressed by culling and starting of again when it comes to feeders.
You should be able to have a colony that is healthy with no respiratory issue or neurological issue.
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