If you are feeding Selective to your rats for the first time, make sure you change from one food to another, gradually over 10-14 days. At first, you should mix a small amount of Selective with your rats' current food, slowly decreasing the old diet, whilst gradually increasing the quantity of Selective. A sudden change in diet can cause digestive upsets - even when you are changing to a better quality diet - so take care!
If your rats are used to a sugary diet, you may find it takes them a while to change, but persevere as it will help to benefit your rats' health in the long term. And don't forget fresh water! Your rats should have an unlimited supply at all times.