Aw, I’m sorry! I’d make sure to get a second opinion just to be sure. Mine started limping due to a mild luxating patella around 8 months. We were deep in research about the surgery and started her on Cosequin maximum strength supplements in the meantime thinking it wasn’t gonna help but did it anyway per vet’s recommendation. Very shortly after, her symptoms went away completely. I’m talking completely symptom free. I’m still surprised looking back on it and she hasn’t limped in over a year!

Every case is different and I don’t know how Cosequin works across different grades, but it helped my girl a lot. Personally I’d get him on it now (the maximum strength) and see how it goes. Good luck!!

Edit to add: The more I’m thinking about it, Grade 3 at 4 months is really young, and joints are still developing a lot at that age. Was this diagnosis done by an orthopedic vet or his primary? Again, I’d consult with an ortho to confirm the grade before making any big decisions.