We get this question a lot.
The short answer is pretty simple: Animals that have a diet of ONLY pasture grasses and/or hay. That's it! (We like to keep it pretty simple here on the farm!) You might also see this as being referred to as 'grass-fed and finished'...and the 'finished' part is what really matters. When WE say grass-fed, we mean 100% grass-fed, PERIOD. This is where the marketing of grass-fed products often becomes confusing and a little misleading for consumers.
You might see some meat being advertised as grass-fed...but the animal is actually "finished" on grain. What that means is that for the last 3-4 months of the animal's life, it was fed corn and other grains to fatten it up and gain weight quicker than it would on a strict grass-fed diet. The grain creates the marbling in the beef that is often desirable for the consumer. (But guess what - our meat marbles pretty nicely on just grass, too!)
Since 100% grass-fed animals don't gain weight as quickly as grain-finished animals, it takes longer for them to be ready for the butcher:
Grain-fed finish in 14-18 months v. Grass-fed finish in 18-24 months
If that grain-fed animal is raised in a feedlot scenario, it's almost guaranteed that they are also consuming a mixture of antibiotics with their feed to keep illnesses at bay.
So, why should you care if your meat is grass-fed, anyways?
Raising grass-fed beef is as much about the nutrition (high in the "good" fats!) as it is about the herd management and environmental benefits.
When an animal is grazing, it of course produces manure, and that manure contains some pretty great nutrients. Since cattle and other ruminants don't care where they are walking or what they are stepping in, they are pushing those nutrients right back into the soil. This has tremendous benefits to help prevent soil erosion and the grasses come back even better the next time around! It truly is about creating a better Eco-system. We like to pride ourselves on how truly spoiled our happy herd of highlands is and we wouldn't want to raise beef any other way!