Does anyone have any suggestions on how to put body on a young male of 18 months, slow maturing breed? I know he will body in time and when he is ready but wondered if anyone had anything I could feed him etc

Time is the only healthy thing :D

Depends if he is typical in body of other males of similar age and type in your breed - if so, he'll benefit more from bodying up at the correct natural pace without intervention of any kind.  If he's *unusually* thin in comparison, you could try adding a little (don't over do it) raw minced tripe to his last meal of the day. 

Regards Teri :)

Why rush him? Time, plenty of exercise (don't confuse body with fat!) & sufficient food will get him there in the end.

Yes you are all right, got another critique this morning telling my he is a lovely boy but needs to body up, will just have to be patient I guess