ALBERT

Description: SUMMARYThe buoyancy and distribution within the rumen of feed particles were measured to assess the extent to which particle buoyancy modulated the movement of particles within and from the reticulorumen. Two experiments conducted in north Queensland in 1988 involved swamp buffaloes (Bubalus bubalis)and crossbred cattle (Bos indicus × B. taurus) fed rice straw with various supplements of energy and protein, lablab (Lablab purpureus), verano (Stylosanthes hamata cv. verano) and two grasses, sorghum (Sorghum bicolor × S. sudanense) and pangola (Digitaria eriantha). Apparent passage rate of particles from the reticulorumen bore an inverse curvilinear relationship to particle size. Passage rate of the smallest particles, retained by a cloth of aperture 50 μm, was faster in buffaloes. Mean particle size of total rumen digesta was smaller in buffaloes than in cattle in Expt 1 with rice straw, but there was no difference between the forage diets offered in Expt 2. The large particle content in digesta (dry matter per kg) in the dorsal rumen was greater than that in the ventral rumen, which in turn was greater than that in the reticulum. The sedimentation rate of particles was measured by a procedure designed to interfere as little as possible with microbial fermentation. A curvilinear relationship was evident between sedimentation rate and particle size; the medium particles sedimented faster than the fine and large particles. Sedimentation rates of some particle fractions were greater in buffaloes than in cattle. Between diets there were marked differences in sedimentation rates of large particles, but these differences decreased with smaller particle size. Large particles from the dorsal sac sedimented faster than those from the ventral sac, and there was no obvious dorsal raft. There was no apparent relationship between particle buoyancy and ease of particle escape from the reticulorumen. The results are discussed in terms of current theories of the physical factors involved in the control of voluntary feed consumption by ruminants.

Description: SUMMARYIntake and digestion by swamp buffaloes (Bubalus bubalis) and crossbred cattle (Bos indicus × B. taunts) of a range of diets were measured in two experiments conducted in north Queensland in 1988. In Expt 1, four animals of each species were offered rice straw ad libitum with a supplement of minerals and urea. The four dietary treatments were (i) no concentrates, (ii)cracked rice grain (900 g/day), (iii) cracked rice grain (900 g/day) plus sunflower seed meal (900 g/day) and (iv) as for (iii) but with 50% of the sunflower seed meal treated with formaldehyde solution. In Expt 2, the same animals were offered two legumes, lablab (Lablab purpureus) and verano (Stylosanthes hamata cv. verano), and two grasses, sorghum (Sorghum bicolor × S. sudanense) and pangola grass (Digitaria eriantha). In Expt 1, voluntary intake of organic matter of buffaloes was 1·22 that of cattle. Concentrate supplementation increased organic matter digestibility and total intake, but did not affect straw intake. Intake of supplements by cattle was poor in the absence of sunflower seed meal. In Expt 2, intake and digestibility was similar in both species but was higher in animals given sorghum compared with the other forages. Total time spent chewing for both species and all diets ranged between 163 and 244 min/kg intake of plant cell wall constituents. The fractional rate of fluid flow from the reticulorumen and the concentration of propionic acid in the rumen fluid of buffaloes were consistently higher than in cattle in both experiments. Cotton and rice straw, placed in polyester bags in situ in the reticulorumen, were more extensively fermented in buffaloes than in cattle in Expt 1. In contrast, there were no differences between animal species in fermentation rates of cotton and ground diets in situ in Expt 2, but a relationship was observed between the relative fermentation of cotton and the relative digesta retention times in the reticulorumen in the two animal species. Microbial biomass, estimated as microbial dry matter per kg dry matter in the reticulorumen, was less (P 〈 0·05) in buffaloes than in cattle in Expt 1; higher concentrations of protozoa were observed in buffaloes than in cattle in Expt 2. Digesta load in the reticulorumen of buffaloes was c. 0·88 that of cattle. In Expt 1, digesta load was inversely related to digestible organic matter intake. The results were consistent with the hypothesis that energy metabolism and digesta load in the reticulorumen interact in the regulation of roughage intake, but it appeared that the lower loads measured in both species in Expt 2 indicated the operation of an unidentified limitation to intake.