Yes, I want to measure growth rate by weight and will measure after every 15 days interval (10 times).

Yes, one group will be under control treatment (placebo) and others under different dosage rate.

Probably one of best measurements of growth is to compare changes in fat, FFM (which includes bone) in the experimental group with the control group.  But that is a real challenge and could be expensive unless you have a nearby lab that has the measuring equipment.  GE Lunar used to have a software program for measuring body composition in animals using a DEXA scan. The animal has to be sedated and you need access to a DEXA unit. As I said, a major challenge but it you could do it, it would be a first class study.

Assessment of energy and nutrient intake would be a key factor.

I guess rabbits will be fed with a combination of hay and concentrates ad lib. Daily intakes of each feed should be measured and compared between experimental groups. Coherences between nutrient intake and individual growth  as well as between supplement group and daily intake could be detected.

Dear Mario González-de la Parra

Yes I want to measure difference in weight gain and each group will consists on 5 rabbits and there will be 4 groups 

i) placebo

ii) low dosage rate

iii) medium dosage rate 

iv) high dosage rate