Grazing: an alternative for low-yield barley crops

An experiment was performed to evaluate the nutritive value of vitreous-grain barley grazed by sheep (instantaneous stocking rate of 66 sheep/ha). Available biomass (2353 kg dry matter (DM)/ha, on average) was determined at the beginning of the experimental period, which lasted for three consecutive weeks, and barley heads, leaves and stems were separated for quantification. Important amounts of Wimmera ryegrass (Lolium rigidum) were also found. Diet selection, intake and digestibility were estimated using the nalkanes technique. Rumen fermentation characteristics and in situ degradation parameters were obtained from rumen cannulated animals. Transit kinetics of barley heads, leaves and stems was also assessed. The proportion of barley heads in the diet consumed was high (0.53 on average) and varied along the grazing period (0.30 in the first, 0.64 in the second and 0.65 in the third week). Wimmera ryegrass was highly selected during the first week of the experimental period (0.7) and much lesser afterwards (0.35). Estimated total DM intake was low (428, 376 and 657 g/day for weeks 1, 2 and 3, respectively), and chan ged with the botanical composition of the paddock and biomass availability. Average DM digestibility of the diet consumed was also low (56%) and decreased as the grazing period advanced (67%, 55% and 47% for weeks 1, 2 and 3, respectively). Rumen pH was, on average, 6.6, whereas ammonia concentration reached a value of 93 mg/l. Proportions of acetic (0.65), propionic (0.15) and butyric (0.15) acids were representative of a rumen environment driven by fibre fermentation. Effective DM degradability of barley heads, leaves and stems was, on average, 81%, 66% and 55%, respectively.