Ruminant digestion .. what do the reticulum and omasum digest?

Question

and what is the role of mucosa in the omasum and mucus in the abomasum?

Answer 1

Lying adjacent to the rumen and separated from it by a low, muscular wall, is the reticulum (honeycomb), a smaller stomach section with a capacity of two to three gallons (0-52 of the stomach's capacity). The reticulum functions much like the rumen with microbial fermentation digestion. The reticulum also functions in the regurgitation of large particles of feed that collect in the reticulum. These large feed particles collect due to the action of the reticulo-omasal o*****e.

The omasum  is a muscular sac with a capacity of three to four gallons (about 8X of the stomach's capacity). Within the omasum, large muscle flaps contract around digesta, squeezing out water and VFA's. The water and VFA's are absorbed across the muscle walls of the omasum. The removal of water is important so digestive enzymes present in the abomasum, the last stomach compartment, will not be diluted. Some grinding may occur in the omasum but is significant only in that the grinding action forces digesta, or partially digested feed particles, into the abomasum.