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One of the most important things to know is that no matter what you read or hear somewhere else, canine diabetes cannot be controlled without insulin injections.
"What is the difference between type 1 and type 2 diabetes?
"Insulin is produced by the beta cells in the pancreas. Type 1 diabetes is due to the destruction of the beta cells with progressive and eventual complete loss of insulin secretion. This type always requires insulin therapy. Type 2 diabetes is characterized by dysfunctional beta cells (irregular insulin production) or the other cells of the body not responding to insulin properly. Type 2 diabetes may or may not require insulin therapy. In general, all dogs have type 1 diabetes and require insulin to control their disease."
With so many abbreviations, one can sometimes get confused. An easy way to separate units (U) from milliliters (ml) is to think about the following: all commonly-available vials of insulin approved for humans are 10ml vials. Most insulin cartridges contain 3 ml of insulin each. Caninsulin/Vetsulin comes in both a standard 10ml vial and a pack of 10 2.5ml vials. Since a U100 1cc syringe holds 1 milliliter of liquid, drawing this amount from the insulin vial would fill the syringe with 100 units of insulin; that would also be 1/10 of an entire 10ml vial and 1/3 of a 3ml insulin cartridge; it would be more than 1/3 of a 2.5 ml Caninsulin or Vetsulin vial.
The syringe in this photo is a 3/10 syringe (this is the smallest size insulin syringe there is; the 3/10 cc syringes are often referred to as low-dose syringes) holding at most, 30 units of insulin. To give a 100lb animal 22 units of insulin, you wouldn't even fill it totally up; 22 units is between the numbers 20 and 25. You'd still have 8 units worth of "room" left in the syringe.
If a dosage looks wrong to you, DON'T BE AFRAID to ask someone for help--your vet, an animal emergency clinic, or a canine  diabetes message board--BEFORE you give an injection of a questionable dose. Delaying a shot if you're not sure is much safer than the alternative.
From the DVM 360 2007 article by Dr. Audrey Cook: 
"Hypoglycemia is deadly; hyperglycemia is not. Owners must clearly understand that too much insulin can kill, and that they should call a veterinarian or halve the dose if they have any concerns about a pet's well-being or appetite. Tell owners to offer food immediately if the pet is weak or is behaving strangely."
Insulin Starting Doses
Pounds converted to kilos and rounded down to whole number
Insulin doses based on 0.25-0.50 IU per kilo, rounded down to nearest whole or half unit