All things are relative. Too much of anything is unhealthy. I would think that several english pea sized snippets of beef liver per day wouldn't be harmful unless 1) your baby already had health problems (in which case you wouldn't be feeding the beef liver to begin with) or 2) the snacks interferred with normal meals.
I use the english pea size as an example because that is what I feel is an appropriate size treat for my guys. Others might differ
