skinny puppy

Hello

I have an 18week old male lab pup (field strain) who is a gundog reject. I got him at 16 weeks old and he was being fed on skinners. He was a bit itchy and gassy so I have moved him onto Nutriment raw as of 3 days ago. Hes getting 750g a day. Plus cut up dried lamb intestine as treats.

His worming was up to date when I got him 2 weeks ago. However I noticed within a week he was on the skinny side and I could kinda see his ribs a bit. I mentioned this to the vet last Friday and she said his weight was perfect at he weighed 14.5kg at 17weeks which seems about right.

A week later and I still think he's definitely a bit too skinny as when I look down on him as his ribcage is too prominent and I can feel the knobbly bits along his spine.

I plan on worming him with VermX from tomorrow just incase. I see no worms in his poo and he's not bloated or scratching his bum.

My question is, is it normal for pups to go through a lanky stage? Hes eating well, playing as normal and nothing else has changed.

Its possible I maybe didn't feed him enough of the skinners as it was just in a bag and the website didn't give feeding guidelines. I was giving him 4 small meals a day, a cup at a time, plus extra for training. I don't think 4+ cups of kibble a day should be enough for him to lose condition. But maybe I grossly underestimated it? He was also a bit over active the last week and didn't nap much during the day. He seems more settled since I moved him onto nutriment.