The digestion of foodstuffs in the stomach of the sheep and the passage of digesta through its compartments

In any attempt to explore the overall changes which foodstuffs undergo while in the compartments of the compound stomach of ruminants, or to determine what happens there to the newly formed products and unchanged residues, certain difficulties have to be faced which are common to all investigations of the passage of digesta through these organs.Interpretation of the nature of the changes is complicated by the fact that food, water and saliva enter the rumen to mix in this diverticulum with a considerable bulk of residues from earlier feeds.Moreover, although digesta pass more or less continuously from the rumen to the omasum, through the reticulum, the contents of the reticulum may not be representative either of the contents of the reticulo-rumen as a whole, or, necessarily, of the material passing to the omasum.Absorption of some of the digestion products through the walls of the rumen and other compartments of the fore-stomachs further complicates the situation.In view of these difficulties it is natural that attention should be given to ratio techniques which employ indigestible markers, since by these means it may be possible to determine precisely the extent to which the digesta in the reticulo-rumen or other compartments differ from the fodder originally eaten.It is important to realize, however, that a change in the ratio of a food component to a marker within the rumen contents could justifiably be used as a measure of the extent of digestion there only if the ratio of these two components of the material leaving the organ were identical with that of the material left behind, at any given time.I n other words, the marker could not function as such in the contents of a diverticular organ such as the rumen if it were passed from this compartment at a different rate from that of the food component under consideration.In order to obtain satisfactory data for calculating the extent of the digestion in the rumen it would be best to examine the digesta, throughout the day, as they leave the reticulo-omasal orifice.At present this procedure is impracticable without undesirable surgical intervention, and it is therefore essential ( I ) to examine the ratios in the omasum or abomasum as well as in the rumen itself and (2) to provide data that extend over, and are representative of, the whole period of the feeding cycle.