The experiment was conducted at a farm located at Jiangsu province from 20 July to 20 August. Forty multiparous Holstein cows with similar ages, parities and lactation days were used and randomly assigned into high producing group (average production 41.44 ± 2.25 kg/d) and low producing group (average production 29.92 ± 1.02 kg/d) with 20 cows in each.Table 1.