4.5 month old kitten won't stop dry nursing on 5.5 month old kitten

Question

Long story short I rescued two kittens near death from two different litters at ages 3 and 7 weeks old. Both are happy and healthy now after seeing the vet countless times. The 7 week old was already interested in solid food, but obviously I gave the 3 week old milk for the first while until I could wean her. Now at ages 4.5 months (female) and 5.5 months (male), the younger has consistently dry nursed on the elder from pretty much the time I got them. At first I wasn't too concerned as my vet told me it was fine for now, seeing as there were no injuries and the female was still quite young. To this day she still tries to dry nurse, and I will generally now try to pick her up and move her away (Is that wrong?). After moving her away, she will immediately run over to get water or food from her bowls. Is she doing this out of hunger? Comfort? Both? Should I be stopping them? So far it seems like still no injuries, and the male doesn't seem bothered. She nurses right under his neck usually, not on his belly. Throughout all of this I've wanted to stop her for the sole reason of not letting this become a habit, but I think it's too late now. What should I do?

Edit- She gets fed plenty. I have had them on vet grade wet food since they started showing interest, and have introduced a vet grade dry food for them. She eats nearly two cans of wet food a day, plus she snacks on the dry food that I have out 24/7. She has been steadily gaining weight and muscle since I got her, and the vet is very happy with her current progress. Yes, I have talked to my vet about their diet. No, you don't need to give tips on how much or how little they should be eating at this age. And finally, yes they will lose access to 24/7 food when they're fully grown. They only get as much food as they do now due to them being young and still growing. They won't overeat, they leave the dry food alone if they aren't hungry. They also have a cat water fountain to encourage them to drink, seeing as a bowl of still water isn't their preference.

Answer 1

The first thing I notice is how early the female was separated. I think the recommendation is 8 weeks at the earliest. (I understand this wasn’t your fault). With that being said I would suspect and do to a degree expect that there are some consequences from this early separation. It wouldn’t surprise me that she would try nursing accidentally on a male. This happens to human babies when they can feel skin - often they start trying to latch even if the person (male or female) isn’t actually trying to nurse them.

I think she also is trying to comfort herself. I would assume this could be similar to cats kneading, which is a behavior developed while nursing.

The other thought is are you sure she is nursing or grooming? Cats bond and show love by grooming each other.

In the end I would just anticipate some sort of consequence from the early separation. I’ve done a lot of research on this for my cat and it can lead to a lot of emotional, behavioral, and physical changes.

I wouldn’t personally find the nursing a problem unless it causes physical harm to the other cat. So I don’t think I would be concerned about stopping it or separating them since she is at least getting food and not starving from unsuccessful nursing. If anything I think they will just become a really bonded pair. That could be problematic if you try separating them later on (if they didn’t live in the same home).

Hopefully things are better and this helps a little!