A review of the development of a bloat-reduced alfalfa cultivar

Abstract

The studies that led to the development of a bloat-reduced alfalfa began in 1970. Initial work focused on the causes of bloat, the characteristics of bloat-safe and bloat-causing legumes and the development of screening methodologies. The characteristics that were examined as causal factors of bloat in legume species included soluble proteins, saponins, absence of condensed tannins, and rapid breakdown of cells in the rumen. The factor or combination of factors responsible for causing bloat in animals grazing legumes have not been clearly identified; however, of the above, rapid cell breakdown was considered to be the most promising line of research to pursue in selecting a bloat-safe legume. A 4-h nylon-bag rumen digestion technique was developed, which was used to assess the initial rate of digestion (IRD) of fresh leaf material in large numbers of alfalfa genotypes. Using this technique on a population of four alfalfa cultivars, four cycles of recurrent selection for low initial rate of digestion (LIRD) were carried out over an 11-yr period. The resulting selected population, LIRD-4, had a vegetative stage initial rate of digestion that was approximately 85% of that of unselected alfalfa. To determine whether this reduction in IRD would reduce or eliminate bloat, grazing experiments comparing LIRD-4 and unselected cv. Beaver were conducted at three locations over 3 yr. Over all grazings, LIRD-4 caused significantly fewer incidences of bloat than Beaver; thus it is a bloat-reduced, rather than a bloat-safe cultivar. LIRD-4 was released in 1997 and named AC Grazeland Br. Key words: Bloat, cattle, alfalfa, low initial rate of digestion, grazing, bloat-reduced alfalfa