This is one of my new rats, he is male and 2,5 months old. I got him 11 days ago and I’ve never seen him groom himself. All I’ve ever seen him do is clean porphyrin off his nose, but I’ve never seen him clean any other body part of his. He and his cagemate are quarantined in my room, so I spend the whole day with them in there. I thought that maybe he’s grooming himself when I’m not looking, but I never even hear him do it (hard to explain, but when rats groom themselves I can hear this specific licking noise coming from them). His cagemate grooms himself frequently. I’m worried about two things. The pee on my rats fur causing a URI because of the ammonia buildup (he smells awful) and penis plugs. How many of these will he get if he’s not cleaning himself properly? Why isn’t he doing it? I thought it’s a basic skill that rats are born with and that they’re not cleaning themselves only when they’re sick or old. He’s fairly healthy aside from a mild URI that’s getting better already, he eats and drinks fine, is active, climbs the cage and plays with his cagemate every day. There are no signs of pain or illness, he’s not hunched over or lethargic, his eyes aren’t squinted and his fur isn’t puffed up. I’m also worried because he’s skittish and dramatic, so he’s not as comfortable with handling. He squeaks a lot and gave me a warning bite when I tried to gently wipe him down, so if the lack of grooming causes him any health issues it will likely result in a lot of stress for him and me. What do I do in this situation? 

I’m worried about my rat seemingly never grooming himself, advice needed