The influence of the stage of the estrous cycle and novel cows upon mounting activity of dairy cattle.

The objectives of this study were to determine directly if mounting activity in dairy cattle varied as a function of stage of the estrous cycle and to determine if mounting by cows could be stimulated when novel estrous cows were introduced. Detector cows were normally cycling. Estrous cows were ovariectomized and injected with estradiol cyprionate and progesterone to induce standing estrous behavior. Familiar estrous cows (prior exposure to detector cows) and novel estrous cows (no prior exposure to detector cows) encountered each detector cow (n = 19) in a one-on-one manner for a 10-min period. Mounting activity by detector cows was determined by observation on d 5, 10, 15, day of estrus and d 5 of the subsequent cycle (52). The first d 5 was considered an acclimation day and was deleted from the data because all estrous cows (n = 4) used were novel. These novel estrous cows then became familiar estrous cows on the subsequent days (10, 15, estrus, 52). On these days, familiar (n = 4) and novel (n = 2) estrous cows encountered individually each detector cow in a prearranged sequence. Stage of the estrous cycle influenced (P less than .001) the frequency of mounting by detector cows. Mounting activity of detector cows was inversely related (r = -.64, P less than .001) to concentrations of plasma progesterone. The introduction of novel estrous cows tended to stimulate (P = .07) mounting when all days were considered. In addition, the introduction of novel estrous cows stimulated (P less than .001) mounting on d 15 and 52. A second experiment was conducted to determine if the introduction of novel estrous cows stimulated mounting in the detector cows on the day of estrus if a longer encounter time (30 min) was used. A total of eight detector cows and eight estrous cows (four familiar and four novel) were used. When the detector cow was in standing estrus, she encountered one-on-one each of two familiar estrous cows and each of two novel estrous cows in a prearranged sequence for 30-min. The introduction of novel estrous cows stimulated (P = .001) mounting by the detector cows on the day of estrus (6.50 +/- .48 vs. 4.37 +/- .48 mounts for N and F cows, respectively). We conclude that mounting activity is reduced during midcycle and that the introduction of novel cows stimulated mounting activity on d 15, day of estrus and on d 5 of the estrous cycle.