Hi! At first glance, I thought that your question has an easy answer, but then I realized that your SRMA is on a preclinical topic.

Regardless of whether you are working on a preclinical or clinical SRMA, your decision in this issue should be based on your pre-existing protocol with pre-specified details. For instance, if you are considering to assess the presence/absence of potential dose-dependent impact of basil on FBG, you have to consider all of the concentrations to be able to do a meta-regression. If you think that getting the FBG measurements in all covered time-points are essential, then you also have to considered repeated-measures techniques in meta-analysis (which can be found easily in the internet, if you are interested).

The other possibility is that you do not need to include all doses and time-points just because the included studies had them in their report. You have to consider that the more time-points and doses considered, without proper statistical control, the higher your false discovery rate. If the ultimate goal is to pursue clinical studies to assess basil as an anti-hyperglycemic agent, please stick to the doses and time-points that you think are likely to be clinically relevant. For instance, monitoring HbA1c and fasting blood sugar among newly-diagnosed human patients with type 2 diabetes upon start of therapy is 12 weeks or 3 months. In the animal model, you might instead consider the time-point that is the closest to 3 months in humans, for instance.

Some references that may be helpful for you:

Article A Guide to Conducting a Meta-Analysis with Non-Independent E...

Article Dose-response meta-analysis of differences in means

Article Meta-analysis of repeated measures study designs

I presume the studies use repeated measures ANOVA for the different time points to analyse the different dosing group. It would be good to include all doses and time points as they would have bearing on the effect size.

However, if different studies have different doses and/or time points, then it’s best to include only the common doses and/or time points in your SR/MA. Hope this clarifies.

Assuming I am understanding correctly, I would combine similar doses and run a meta-analysis. If you are lucky, you will be able to compile all the data and run a dose-response analysis.