Thirty second-parity Chinese Holstein cows in mid-lactation with a body condition score of @ , weighing @kg and producing @ kg milk per day were randomly assigned to @ of the @ diets ( n = @ per treatment ) : @ ) low-concentrate mixed forage diet ( LCF ) with a concentrate to roughage ratio of @ : @ ; @ ) high-concentrate corn straw diet ( HCS ) with a concentrate to roughage ratio of @ : @ ; @ ) low-concentrate corn straw diet ( LCS ) with the same concentrate to roughage ratio ( @ : @ ) as LCF .