Mounting behavior as affected by stage of estrous cycle in Holstein heifers.

Nine Holstein heifers whose estrous cycles were synchronized were observed during three subsequent consecutive cycles. Observations of heifers during each periestrus period began when the first heifer reached day 15 of an estrous cycle and ended 36 h after onset of estrus for the ninth heifer. There were 118 1-h observations at 6-h intervals during the three periestrus periods. Estrous cycles were divided into postestrual, luteal, preestrual, and estrual stages by blood progesterone profiles and estrus. Heifers of these four stages accounted for 27.5, 48.3, 15.4, and 8.8% of heifers available to mount during the 118 observations, and heifers of each stage made 9.0, 5.2, 18.9, and 66.9% of attempted mounts. When number of heifers in estrus simultaneously increased from one to five, total attempted mounts and stands per hour increased from 10.1 to 63.5 and from 4.5 to 48.5. Stands per heifer per hour increased significantly as number of heifers in estrus increased from one to two and tended to increase as number in estrus increased further. Presence of one preestrual heifer in a group containing one estrual heifer increased total stands per hour from 2.3 to 5.0. Efficiency of detection of estrus may depend on proportion of animals within estrous cycle stages that have highest mounting activity.