Twenty-four pairs of monozygotic twin dairy cows (Danish Friesian and Red Danish) were assigned to four groups of 12 in a balanced incomplete block design. Group E: loose housing, free access to feeding table, deep bedding, a yard and pasture, milking twice a day. Group N: tie stall, concrete floor plus 1 kg straw, milking twice a day, no exercise. Group I: tie stall, rubber mats plus 2 kg straw, milking four times a day, no exercise. Group IE: similar to Group I, except for 1 h daily exercise. In general the duration of the lying-down pattern was significantly longer in the tie stalls and interruptions of the lying-down movement occurred more frequently in the tie stalls than under loose housing conditions. The duration of the lying-down movement was significantly longer in Group N than in Group E. Cows in Group E had significantly shorter total lying times compared with cows in the tie-stall groups, while no significant differences among the groups in the tie stalls were found. In Croup E the mean duration of resting bouts (lying periods which included one or more short standing periods for a maximum of 15 min) was significantly higher in the pasture. Lying flat on the side and with the head back or on the ground occurred more often in the pasture than in the deep-bedding area. In the tie-stall groups 1 h of daily exercise had no significant effect on time spent lying or the duration of resting bouts. The kneeling duration was shorter in the groups with than without 1 h of exercise. There were no inflammations of knees and hocks in Group E, but there were from eight to ten hock inflammations in each of the tie-stall groups. The frequency of trampled teats was significantly higher in cows kept on a concrete floor with a small amount of straw (Group N) than in cows kept on rubber mats with a large amount of straw (Group I and IE). Altogether the results suggest that the act of lying down in the stalls was aversive to the cows and that the lying area and/or the tie-stall system increased the risk of injuries to tethered cows.
