U have to read about diabetes animall models. Firstly u should decide severe diabetes animal it s mean that u should inject 65 mg/100 g iv. at once. All animals blood glucose level will be more than 350. Or if u want moderate diabetes animal so u should inject 45 mg/100 g iv. at once. Your experimental animal how long time must survive u can decide that diabetes strengt. 

i use intraperitoneal injection 100mg/kg bw, according to the protocol i used which is 100mg/kg bw on day 1st then next dose is on day 14th with 50mg/kg bw stz, but the result is 6 animal develop diabetes on day 7, and 10 animal develop diabetes  (blood glucose level >300) on day 14, following by 3 animal diabetes on day 21 (7 days after second injection), i use balb/c albino mice,  the rest animal still remain normal (21 mice out of 40 mice), i wonder what can cause it, and how to make the other mice develop diabetes

Because u did injection ip instead of iv. I u choose iv injection your all experimental animal will have diabetes at first shot, approximately within  24 h.

http://www.ncbi.nlm.nih.gov/pubmed/21228065

http://www.ncbi.nlm.nih.gov/pubmed/23916662

thank you, i was found a journal with the same method, induction of stz in 5 consecutive day in low dose.

thank you Mr Yusuf Öztürk, i am studying the effect of vanadyl sulfate too. I am studying molecular effect of vanadyl in pancreatic beta cell of diabetic mice induced with streptozotocin, especially the regulation of apoptotic and proliferation. i belive your paper will help. 

best regards,  

nisak

Good luck for your research, in which Dr. John McNeill of British Columbia Univ has extensive research, while I had only a few on this subject