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

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 = ax b 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.