The effects of diet supplements and gamma irradiation on dissimilation of low-quality roughages by ruminants: II. Effects of gamma irradiation and urea supplementation on dissimilation in the rumen

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Abstract
SUMMARY: Results of two in vivo sheep experiments in which gamma-irradiated material in teryleno bags was fermented in the rumen are reported.Exp. I concerned the testing of rice straw, nassella (Nassella trichotoma) and cotton lint, each subjected to six dose levels of gamma irradiation (0, 5, 10, 25, 100 and 200 Mrad) when wet and when in the dry state. The tests were made in sheep fed either a lucerne hay or a rice-straw base diet.Dry -matter disappearance of all test materials was influenced by irradiation treatment: levels of 10 and in some instances 25 Mrad depressed, and other levels substantially enhanced, intraruminal degradation rate tested over 72 h. Materials irradiated in the dry state were better dissimilated than those irradiated in the wet state.On severe shaking for 14 h in water, solubility values as high as 35 % were obtained for irradiated test materials receiving the highest dose of irradiation but such values were never of the same magnitude as total dry-matter losses in the rumen. When irradiated material was immersed in gently flowing water for 12 h solubility values of 1 % were found for material dosed at 100 or 200 Mrad and of nil for other dose levels. At no level of irradiation was solubility depressed. It was concluded that enhanced losses of irradiated dry matter in the ruminal environment arose substantially from fermentation.Intraruminal dissimilation of irradiated test material from terylene bags was always greater on lucerne hay base diets than on rice straw base diets.Exp. II investigated the influence of urea supplementation, at levels of 1 % and 2 % of diet, on the dissimilation of irradiated test samples of cotton lint and rice straw for sheep fed a rice-straw base diet.Similar effects of irradiation on cotton lint and rice straw to those found in Exp. I were observed. Overall, urea supplementation depressed dissimilation rate of rice straw and severely depressed degradation of cotton lint irrespective of irradiation dose up to an irradiation dose level of 100 Mrad. It is concluded that urea supplementation per se depressed the activity of cellulolytic organisms.It is considered that feeding trials with low-quality roughages irradiated at levels at or greater than 25 Mrad are warranted.