Calf Rumen Images
The calf fed grain in addition to hay and milk has a larger stomach, and greater rumen development. Note the healthy, dark coloration and visible rumen papillae.
The rumen of the calf fed milk only is considerably smaller than the calf fed milk and grain.
Developing a healthy rumen is important to ease the transition from a pre-ruminant to a ruminant animal.
The esophageal groove is formed by muscular folds of the reticulum, which you can easily see in these photos.
Both of these calves exhibit dark coloration of the rumen and reticulum, but if you examine the rumen it is apparent that the calf fed hay has much less papillae development.
Both of these rumens are very large, but when it comes to rumen development size isn't everything!
The importance of grain in developing the rumen should be obvious from the follwoing two photos.
The pictures below show the omasum of a calf at 6 weeks of age.