serious question because I can't find the answer. I am currently doing an animal study, and I am preparing a manuscript about this. However, I am thinking of adding a second part to this paper by doing a systematic review also. Thus, to make it an article that has both original research and systematic review. The reason to do this is that there are some limitations of this animal study, and I think a systematic review can further back up the conclusion drew by the animal study. In another way, the systematic review has its limitation as well, and the conclusion drew from my animal study can back up the statement from the review. Kinda reciprocal relationship between these two and I feel it can make the quality of this paper better. So my question is if this is acceptable? I haven't seen a study that has part one about original experimental research and part two about a systematic review.
Your paper should have a complete convincing argument leading to your conclusions. If as the author you think a (perhaps unusual) systematic review of the literature strengthens your argument in an important way then include it.
Perhaps you could make it somewhat shorter than systematic.
You could include a statement in the paper or a cover letter to the editor explaining briefly why this material is necessary.