Factors limiting the intake of feed by sheep. 10. The effects of concentrate supplements on the voluntary consumption and digestion of a medium quality roughage

Feed intake and digestion studies were conducted with sheep offered a medium quality roughage and given various concentrate supplements. The provision of supplements in amounts equal to c. 23% of voluntary roughage consumption always decreased roughage intake. The decrease with wheat-based supplements was little affected by supplement feeding frequency, by use of ground grain rather than whole grain or by the provision of additional essential nutrients, but its magnitude was reduced by c. 30% with use of buffer salts to prevent decline in rumen digesta pH. The supplements were associated with less digesta in the alimentary tract and less rumination. Supplements increased the rate of liquor outflow from the reticulum and the rate of marker clearance from the reticula-rumen. The rumen digesta and reticulum digesta differed with respect to particle size distribution and only some 30% of the organic matter in reticulum digesta was in particles too large to pass to the omasum. The data were considered to be consistent with a concept that the regulation of roughage intake involves an interplay between the animal's energy metabolism and the quantity of digesta in the reticula-rumen and to indicate (i) some discrimination against the larger particles in digesta flow from the rumen to the reticulum, (ii) appreciable discrimination on the basis of size of particle in digesta flow from the reticulum to the omasum, and (iii) regardless of state of subdivision, constraints applied to digesta passage to the omasum which could have affected the level of feed intake achieved.