Sheep are part of the ruminate classification of animals. Like cows they have 4 chambers in their stomach. Sheep are mostly grazers. At birth the lambs rumen and reticulum are  not yet functional. They start to nibble on dry feed which stimulates the development of the rumen and reticulum. This is why the lamb needs to eat creep feed. At around 2 weeks old the lamb can be introduced to the creep feed. Creep feed is highly digestible for the lamb, it is feed that has been ground, cracked, rolled, pelleted for the lamb. Lambs cannot digest whole grain this is why they need creep feed. At around 60 days old their rumen and reticulum are fully functional. The lambs that are fed creep will have quicker rumen development than the lambs that are only feeding on forage. Sheep are natural grazers, they eat grass, forbs, clover  hay, silage and weeds. When you are introducing grain to sheep and lambs you must do it slowly. They will produce too much lactic acid which can be fatal for the