Scanning electron microscopy of ruminal papillae in calves fed various amounts and forms of roughage.

Twenty neonatal calves were fed milk plus 1 of 4 rations ad libitum: pelleted concentrates plus alfalfa hay, pelleted concentrates plus ground alfalfa hay, pelleted concentrates alone, or pelleted concentrates containing whey. Eight calves were killed at 4 weeks of age, and 12 calves at 6 weeks. The ruminal mucosa was examined grossly, by light microscopy, and by scanning electron microscopy. Well-developed differences among groups were evident in calves at 6 weeks of age; changes at 4 weeks were similar, but less developed. In 6-week-old calves fed concentrates plus alfalfa hay ad libitum, papillae were flattened and tongue shaped on the ventral floor of the atrium ruminis (cranial sac). Calves fed concentrates plus ground alfalfa had tongue shaped, rounded, and finger-like papillae. Calves fed concentrates alone or concentrates plus whey developed small, nodular, branched papillae which were cauliflower shaped and severly parakeratotic and were arranged on transverse folds on the floor of the atrium ruminis and on zigzag folds elsewhere in the rumen, except on the dorsal wall in contact with the gas bubble. The transition from tongue-shaped to nodular-shaped papillae under the influence of ration occurred last on the floor of the atrium ruminis. At least in 6-week-old calves, that site generally is not typical of changes in most ruminal papillae.