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FORAGE & GRAZINGLANDS

Bloat Reduction Potential of an Alfalfa Cultivar Selected for Low Initial Ruminal Disappearance

^a Facultad de Ciencias Agrarias, Universidad Austral de Chile, Campus Isla Teja, CC 22, Valdivia, Chile
^b Estación Experimental Manfredi, Instituto Nacional de Tecnología Agropecuaria, Ruta Nacional N° 9 Km. 636, 5988, Manfredi, Córdoba, Argentina
^c Facultad de Ciencias Agropecuarias, Universidad Nacional de Córdoba, CC 509, 5000, Córdoba, Argentina

^* Corresponding author (mbernald{at}puc.cl).

Foamy bloat causes large economic losses in beef and dairy grazing systems based on alfalfa (Medicago sativa L.). Dry matter (DM) disappearance at initial stages of rumen fermentation is associated with bloat. The National Institute for Agricultural Technology, Argentina, developed a cultivar of alfalfa (Carmina) with low initial ruminal DM disappearance (LIRD). To study the bloat reduction potential of Carmina, a grazing trial using steers was conducted. The trial was repeated in 10 periods using the cultivar Barbara as control. Bloat frequency and severity were estimated by direct observation of each animal after the start of grazing. Just before grazing, forage samples were taken so as to characterize agronomic properties and chemical composition of the pasture. Cultivars were not different in crude protein, neutral detergent fiber, acid detergent fiber, and lignin concentration (248, 317, 239, and 58 g kg^–1 DM, respectively). Overall, Carmina reduced bloat occurrence (P < 0.01) by 25.2% compared to Barbara, but presented a lower forage DM yield per hectare and a slight more advanced maturity stage (cultivars were grazed from early to mid-bud). Selection for LIRD was an effective way to reduce bloat risk.

Abbreviations: ADF, acid detergent fiber • BW, body weight • CP, crude protein • DM, dry matter • EP, experimental period • HA, herbage allowance • IRD, initial ruminal disappearance • LIRD, low initial ruminal dry matter disappearance • MSC, mean stage by count • MSW, mean stage by weight • NDF, neutral detergent fiber