If it is an older, solid piece of lumber then it is normal for it to check. I am surprised that it is still checking if it is very old.
The checks are allowed to penetrate up to half way through before they become an issue at bearing points. If it is only checked halfway through then you should be fine. If it is checked beyond the 1/2 way point then it needs to be either replaced or re-enforced.
The codes do not have prescriptive re-inforcement requirements so it will have to be designed if you plan on being compliant with structural code requirements. If it becomes a problem it is best to simply replace it. Our area has a lot of replacements.