Hi Larissa,

First things first, to collect serial blood samples in freely moving conscious and stress-free rats, my best advice to you is to have a venous access jugular or femoral vein cannulation / catheterisation established (under anesthesia), this insures standardised and reproducible, with as much as little margin of errors, data. This is what we found over many years of manually collecting serial blood samples to be very much consistent. But requires training and certain technical expertise.

To decide how much blood you can withdraw from a single rat in one take or over several repeated samples on one day , one weak and/or one month i would direct you to the following guidelines:

https://www.nc3rs.org.uk/rat-decision-tree-blood-sampling

and

https://animal.research.uiowa.edu/iacuc-guidelines-blood-collection

to analyze for : Amylin (Active), C-Peptide 2, Ghrelin (Active), GIP (Total), GLP-1 (Active), Glucagon, IL-6, Insulin, Leptin, MCP-1, PP, PYY, TNF-α. you need to collect whole blood samples to eppendorf tubes containing protease inhibitor cocktail and Diprotin A (a dipeptidyl-peptidase-IV inhibitor) spin it at 2,000×g for 10 min and collect plasma and stored at −80 °C. when ready use the MILLIPLEX MAP Rat Metabolic Hormone Magnetic Bead Panel - Metabolism Multiplex Assay to generate your data.

for hematocrit (PCV) you need 75 microL heparinized capillary tubes and hematocrit centrifuge, and you can manually calculate using the formula HCT = (MCV x RBC count)÷10

For liver-enzymes, triglycerides and bile acids assays and methods please check out this good paper:

Article Apple Pomace Consumption Favorably Alters Hepatic Lipid Meta...

Best wishes and good luck with your research.

Ghanim