the forcing thing is a bad idea..... They can - and as you know, will go months without a movement. I dont think you have anything to worry about if your animal acting and looking healthy.
in regards to the asf rats thing.... maybe its the calcium content of the fur that helps it pass quicker.
so long as your blood is passing urates and doesn't look like sausage - bursting at the seems, it should be fine.

byron.d