The flow of feed residues through the gastrointestinal tract of ruminants

Abstract

The results of three different experiments involving different aspects of digesta flow in ruminants are presented in five chapters. In experiment one, increasing level of either rice hulls or ground hay from 0 to 30% in a roughage-corn diet fed to beef steers progressively reduced compartmental mean residence time (CMRT) of corn (95 to 40 h) while further increases to 60% were without effect. In experiment two, the feeding of a protein deficient diet to lambs reduced voluntary intake, decreased dry matter load in the ruminoreticulum but not in postruminal segments, decreased CMRT in the ruminoreticulum, decreased protein outflow from the ruminoreticulum and other segments and decreased serum levels of asparagine, phenylalanine, threonine, tyrosine and valine. When expressed relative to voluntary intake, protein and amino acid outflow did not differ for lambs fed the protein deficient and protein adequate diets. This and other evidence was discussed which suggests that amino acid flux to the tissues was active in metabolically regulating voluntary intake. Also, in experiment two, the retention time of the intrinsic indigestible neutral detergent fiber was not different from that of rare earths bound to the cottonseed hulls containing the indigestible neutral detergent fiber. This result was interpreted to validate the use of rare earths as particle flow markers. A third experiment involved different rare earth markers applied to different size feed particles and dosed into and sampled from different gastrointestinal sites of Holstein heifers. The results were interpreted to indicate the existence of four mixing pools corresponding to; 1) ruminoreticular particle escape, 2) ruminoreticular rumination, 3) the abomasum and 4) postabomasal segments of the gastrointestinal tract. Homogeneous flow of different size particles and solutes occurred through the postabomasal segments which accounted for essentially all of the non-mixing, displacement flow.