Multiple injections of 15mg/kg or one injection of 40-90mg/kg.

The doses proposed by Liu are for inducing type 1 diabetes model. For type 2 diabetes, you can use:

1- 50 mg STZ 30 min after 120 mg nicotinamide.

2- High fat diet for 4 weeks followed by single i.p. injection of 30 or 35 mg STZ.

Doses given on the based of Type I or Type II induction

35 mg STZ with diet for Type II

50 mg STZ  (minimum 2 times 1st day and 3rd day) This is my personal experience as getting rats diabetic first stretch is bit tough so have to give 2nd time STZ.