Whole crop rice silage (WCRS) has recently attracted attention as forage for dairy cows. The nutritive value of WCRS (Forage rice cultivar: Nishiaoba) was examined by a balance trial (Experiment 1). The forage rice was harvested and ensiled in two ways (round-baled silage and container silage). On a dry basis, the contents of metabolizable energy, crude protein and neutral detergent fiber in WCRS were 1.7 Mcal/kg, 6.3% and 47.4%, respectively in round-baled silage, and 2.0 Mcal/kg, 7.4% and 46.6%, respectively in container silage. The feed value of Nishiaoba WCRS for lactating dairy cows under high ambient temperature was also investigated (Experiment 2). The daily milk yields of cows fed WCRS as part of their total mixed ration (rice TMR) and oats hay as part of their TMR (oats TMR) were 29.7 and 30.1 kg, respectively. The dry matter intakes (DMI) of cows when fed the rice TMR and oats TMR were 18.5 and 19.7 kg, respectively. There were no significant differences in DMI, milk yield and composition between cows fed the rice TMR and the oats TMR. The energy retention of the cows fed the rice TMR was significantly lower than that of the cows fed the oats TMR (P