Four healthy nonpregnant, nonlactating, ovariectomized Holstein cows (age 6.2 to 8.2 yr; body weight 610 63 kg) were used in this study.
A bilateral ovariectomy was performed in each cow by lateral laparotomy at least 3 mo prior to the experiment to exclude the effects of gonadal steroid hormones.
The cows were housed separately and loose tied at least 1 wk prior to the start of the experiment.