Just as people have to learn how to use a knife and a fork or chopsticks, animals have to learn how to tear grass, nip off twigs and pick leaves.
Principle: Animals must learn how to forage.
Don't believe us watch the video (on youtube): Foraging Skills
Replacements: Buy replacement animals from areas with the same forage type. For example, if you have shrubs, replacements should have experience browsing shrubs similar to the ones that grow in your area.
Training young animals: Young animals need to learn to harvest foods they will be expected to harvest later in life. For example, in pasture based dairies, cows actually have to learn to eat grass. Cows reared on concrete don't know grass is food let alone how to eat it. Replacement heifers should be either left with their mothers for the first six to eight weeks of life or put on grass soon after birth so they can acquire the skills they will need later in life. In addition, bulls or heifers reared drylot and fed harvested foods will likely perform poorly when forced to forage on rangelands or even on pastures later life because they don't know how or what to eat.