I've got some problems with selecting right model/method in my analysis.
Two groups of animals (differ by "Treatment") were measured from 1-st to 42-nd day, one common value for each group was measured by each day (food consumption per day). I need to compare this groups and I want to use ANCOVA with "Treatment" as fixed effect and "Day number" as covariate in the model.
There are many examples which contain covariates with some sort of randomness in their distribution (like weight, age, IQ, etc., where we can't directly control this variable). But in our experiment we eliminate this variation by measuring groups day by day. Is it correct to use "Day number" as continious covariate?
Maybe the whole model is incorrect and you can suggest right one?
To be more concrete I would like to present the scatter plot of my data: