The American Grassfed Association defines grassfed products from ruminants, including cattle, bison, goats and sheep, as those food products from animals that have eaten nothing but their mother’s milk and fresh grass or grass-type hay from birth to harvest – all their lives. 

For grassfed non-ruminants, including pigs and poultry, grass is a significant part of their diets, but not the entirety of their diets, since these animals need to consume grains.  Many products have been, and continue to be, marketed as “grassfed”, when grass is only a part of their diet.  This lack of standardization on grassfed products is just one of the reasons the American Grassfed Assocation is pushing hard for strict U.S. Department of Agriculture guides on grassfed marketing claims.

References

http://www.americangrassfed.org/faq.htm