Mounting Behavior as Affected by Stage of Estrous Cycle in Holstein Heifers

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Abstract
Nine Holstein heifers whose estrous cycles were synchronized were observed during 3 subsequent consecutive cycles. Observations of heifers during each periestrus period began when the 1st heifer reached day 15 of an estrous cycle and ended 36 h after onset of estrus for the 9th heifer. There were 118 1-h observations at 6-h intervals during the 3 periestrus periods. Estrous cycles were divided into postestrual, luteal, preestrual and estrual stages by blood progesterone profiles and estrus. Heifers of these 4 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 1 or 5, total attempted mounts and stands per h increased from 10.1 to 63.5 and from 4.5 to 48.5. Stands per heifer per h increased significantly as number of heifers in estrus increased from 1 to 2 and tended to increase as number in estrus increased further. Presence of 1 preestural heifer in a group containing 1 estrual heifer increased total stands per h 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.