Okay let's see if I can explain this without being too graphic LOL.

Rat breeding, at least these regular large rats, is basically this for the male....

hop on, hop off, lick your best bits, take a quick break, grab a bite to eat or a drink, hop on, hop off, lick your best bits....and so on....

Basically just instinct. He's trying to make sure that his genetics are the ones passed on and not another wandering male rat that might come by. Once he's bred her a few times a mucus plug develops in her vagina to prevent further breeding attempts since she is now impregnated. The male will at that point leave her be until after she's delivered the litter she's now carrying.

Lab rat females like our big rats are usually receptive to breeding and will stiffen and squat to allow the mating if they are in their 4 to 5 day heat cycle. ASF's are a bit different that way. The females make the male chase them repeatedly before they'll allow mating. I'm not sure quite why but it's likely some form of a fitness test LOL. If he's not fast and tricky enough to catch them, then he's not a good potential mate.