RELATIONSHIPS BETWEEN RUMINANT BLOAT AND THE CHEMICAL COMPOSITION OF ALFALFA HERBAGE. I. NITROGEN AND PROTEIN FRACTIONS

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Abstract
Daily bloat incidence was recorded in cattle fed alfalfa silage at Kamloops, British Columbia, during the 1973, 1974 and 1975 growing seasons. The overall bloat frequency was 3.32% of animal days. The occurrence of bloat differed significantly (P < 0.05) among years, but there were no significant associations (P < 0.05) between bloat and alfalfa cultivars, number of harvests or height of forage stand. Feed samples were collected each day and stored (−20 C) for measurements of chemical composition. The coefficients of determination relating the occurrence of bloat to the chemical parameters were: total nitrogen (N), 0.09; insoluble N, 0.06; soluble N, 0.12; soluble protein N, 0.11; soluble non-protein N, 0.08; fraction I protein, 0.05; fraction II-5 protein, 0.07; fraction II-8 protein, 0.10; fraction II-9 protein, 0.10; fraction II-12 protein, 0.08; lipoproteins, 0.01, soluble protein measured by the biuret method, 0.11; and foam volume, 0.05. There were no significant relationships between the chemical parameters and the number of bloated animals. The relationship between probability of bloat (y) and soluble protein N (x) was described by the curvilinear function Y = axb where a = 0.003 and b = 1.86. On the basis of this function a 50% reduction in soluble protein concentration will be required to develop a bloat-safe alfalfa cultivar by plant breeding.