Calf doesnt seem to be growing well

I have 2 steers. 1 is 13 weeks old and the other 10 weeks. Both are Angus cross (commercial beef) Both were orphaned and raised on a bottle until 8 weeks. They have free choice coastal hay and free choice grain/mineral. The younger one just isnt filling out. the older one was filling out nicely by 8 weeks but the younger one still looks like a 4 week old. Both have had all their required vaccs and deworming. The younger one was castrated at a few days old while the older one was castrated at 8 weeks old.

Could the younger one just be a runt? will he catch up? They will both go out on pasture with 1 hour access to grain feeder daily in June

I think all calves react differently to being put in that situation. It could be partly due to genetics and being a runt but it may be just a slow start due to not having a momma. It could be that he has or had an infection of some kind that held him back. It could be that his rumen has not been functioning properly. You may check with your vet about rumen enhancing additives and maybe go ahead and run some penicillin through him. Just some thoughts. Good luck to you.

I dont know what other people do but we always leave them on milk replacer longer or atleast til its obvious they are eating the other feeds very well. Bottle calves do seem to start a bit slower but most of ours catch up. I agree with mayve giving so probiotics or vita charge past to make sure its gut is working. A shot of pen might also help get rid of any infection.

When you say free choice grain, exactly what is the "grain"? Calves little stomachs can't handle like a strait full feed grain like say corn very well for instance. I personally would rather hand feed calves a feed developed for calves @ their age than free choice it. Remember that their stomachs are small @ this age. It won't take much feed to do the trick. More at this size would not be better.