"His sheep has milk."
Translation:Oaia sa are lapte.
To be honest, I rarely use "sa/său/săi/sale" because we cannot know the owner's genre.
"Oaia sa are lapte" can mean also "His sheep has milk" or "Her sheep has milk" ("Oaia lui are lapte" or "Oaia ei are lapte") And to answer your question, there is no difference. You can use both, if you like :)