Forage selection by beef cows grazed on a dwarf bamboo (Pleioblastus argenteostriatus f. glaber)-dominant pasture

This study investigated the influence of forage selection on the quality of the diet ingested by beef cows grazed on a dwarf bamboo-dominated pasture. For 13 days each in spring, summer and autumn, eight Japanese Black cows were grazed on a 1.8-ha dwarf bamboo (Pleioblastus argenteostriatus f. glaber)-dominant pasture during the day. The plant species and number of bites of each species ingested by the cows were recorded, and plant samples were hand plucked to imitate the behavior of the cows during the grazing time on the seventh and 13th days of each period. The botanical and chemical compositions of the available pasture were systematically estimated by sampling 28 plots. The cows slightly avoided dwarf bamboo and preferred grasses on the seventh day of each period. On the 13th day, the cows ate any available forage in the pasture. The selected forages were higher in crude protein and in vitro digestibility and had lower insoluble protein, neutral detergent fiber and lignin contents than the forages available in the pasture during a season. The frequency of the botanical groups selected by the cows was different in autumn from that in spring and summer, and a substantial increase in grasses and a decrease in P. argenteostriatus f. glaber among the selected forages were observed. Although the botanical groups selected by the cows were relatively different between the seasons, an increase in the levels of unavailable fractions such as lignin and insoluble protein and a decrease in in vitro digestibility were observed as the seasons progressed. Thus, the cows could not avoid a decrease in their diet quality in autumn. The selection of forage improved the nutrient intake of the beef cows in terms of chemical and digestible components; however, in a dwarf bamboo-dominated pasture, there is a substantial limitation in the effectiveness of forage selection.