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Studies on forage cell walls: 4. Flow and degradation of alkali-treated rice hull digesta in the ruminant digestive tract
Published online by Cambridge University Press: 27 March 2009
Summary
Sheep weighing 27 kg live weight were fed ad libitum three pelleted diets containing alkali-treated ground rice hulls (0, 5 and 15 g NaOH/100 g rice hull dry matter) in a 1:1 ratio with ground non-alkali-treated lucerne and were fed a fourth diet comprising the above control pellet fed ad libitum with a wheat grain supplement to determine the effects of alkali treatment and of energy supplementation on the digestion of cell walls and to assess the dynamics of flow of digesta through the gastrointestinal tract.
Flows of organic matter (OM) and nitrogen (N) to the duodenum were not different for the four diets, but daily whole digesta flow past the duodenum was greater (P < 0·01) for the two alkali-treated diets. Alkali treatment of rice hulls increased the percentage of total digestion of OM that occurred in the foregut (68%) compared with non-alkali-treated diets (52%), did not increase total volatile fatty acid concentration in rumen liquor, or adversely increase rumen pH. The capability of rumen microbiota to synthesize ammo acids was not adversely affected by alkali treatment. The percentage unit digestibility of cell wall constituent OM in the whole tract was increased approximately 1·6-fold by alkali treatment. Grain supplementation increased diet digestibility.
Scanning electron microscope studies revealed confirmatory visual evidence of enhanced degradation of alkali-treated rice hulls in the tract. It is clear from these studies that alkali treatment has caused sheets of silicified cuticle on the outside of rice hulls to dissolve and to lift away from the underlying lignocellulosic (palisade) matrix. It is also clear that this matrix material is itself heavily mineralized. Disappearance of silica across the gut wall was greatest for animals fed alkali-treated diets. No clinical signs of urolithiasis were seen. Sheep readily coped with the sodium intake (33 g/day) associated with alkali-treated diets, partially by an increased water consumption and a greater ruminal and intestinal absorption of this electrolyte.
It is calculated that the OM intakes recorded and nutrients released from alkalitreated rice hull diets provided between 500 and 600 kcal net energy/day.
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