I have weight data from 4 animal groups measured at multiple time points. Some data at 2 time points is moderately non-normal. Should I still use repeated measures ANOVA with Greenhouse–Geisser correction, or switch to a non-parametric test? Also, to check for baseline differences, would ANCOVA be more appropriate? I'm not very confident with stats, and my main aim is to assess treatment effects on weight over time. Any suggestions on the best analysis approach?