
Why are you trying to restrict nursing? Mum will know when she no longer wished to allow the pups to nurse. She will usually start this at around 5 weeks allowing access less frequently.
My bitch had pups just 10 weeks ago, and this time only hreared 4 compared to 9 last time. She is a good example of a very confident bitch, who never avoided her pups in order to wean them, but would stop them nursing when she wanted by telling them off. She was still giving regular feedsat 7 weeks this time (I mean at least 4 a day) then one day decided that she had best get this weaning accomplised and over a couple of days allowed them shorter and less frequent access to the milk bar, and within 3 or 4 days she might have given them a quicfk cursory suck, but as the milk had all but dried up, they lost interest very quickly.
When she had the large litter she did the same but at about 5 1/2 weeks, I think she thought she was underworked this time, LOL/
Anyway her milk bar has all but disappered 2 weeks after pups left, and just the nipples are still large. she would be fit to show, if she had a coat.
Leave it to the bitch to decide when she has enough. As long as she can always get away from pups when she wants then there isn't a problem, and I have found with pups I kept that sometimes they allowed a bit of comfort sucking up to about 12 weeks, but I don't think they get much milk. All my girls have lways had no trouble with their undercarriage. My oldest bitch only developed a bit of a saggy tum after spaying.