How are you thawing the rats? I have a stubborn blood that will only eat if her meal is delivered really warm. I feed her first but sometimes she still has an issue so I will warm the meal in hot water again and that does the trick.
I use a ziploc bag and warm water. I usually just leave them in the same water until thawed which sometimes cools to much for her liking so I will give hers a second hot water treatment to warm hers up just a bit more. That always does the trick.