The ad is misleading you.  Just as women in famine conditions aren't producing skim milk, hams aren't producing Oreo cream.  If the mom's diet is lacking, the body will leech what it needs from her stores to get the baby what it needs.  The body doesn't run out of short, immediate supply of vitamins and say, "fuck it, put the Big Mac through."  Suckling a ham teet is definitely a gross visual but from a nutritional aspect...unfortunately that actually is better.