PSI-9 - An evaluation of cow activity traits during the breeding season to determine the effect on conception method.

Abstract: The objective of this study was to evaluate grazing activity traits and their influence on conception method during the breeding season. In a 1-year study, crossbred Angus cows (n = 29) were blocked by age and then randomly assigned to be fitted with a Knight global positioning system (GPS) tracking collar. All cows, except first-calf heifers (n = 12), were synchronized for fixed-timed artificial insemination (TAI) utilizing a 7d CO-Synch + CIDR protocol. Bulls and first-calf heifers were turned out on native rangeland with the cowherd 7d after TAI for a 65d breeding season. Cattle were managed in an intensive rotational grazing system (15 pasture movements in the first 21d of the breeding season) with several daily pasture movements. Cows were retrospectively classified into the following groups for comparison: conception to TAI (AI; n = 12), Bull-bred (BB; n =17). Total daily distance traveled (km/d), average daily elevation gain (m/d), and percentage of time spent grazing challenging topography (i.e., > 15% slope) were measured during the first 21d of the breeding season. Data were analyzed using the MIXED procedure in SAS 9.4. The model included the main effects of conception method, pasture, and their interactions. Total daily distance travelled, and elevation gain exhibited a conception method × pasture interaction (P < 0.05). Amongst the fifteen pastures, AI cows in pasture F (d 7 of breeding season, 7.69 ha, min. elevation 36.27 m, max elevation 46.94 m) travelled further than BB cows (P < 0.001). Overall, cows that conceived to AI tended to travel further each day when compared to BB cows (P = 0.06). Bull-bred cows exhibited a greater daily elevation gain in pasture F when compared with AI cows (P ≤ 0.001). The percentage of time spent on a challenging slope did not differ among cows (P = 0.20). These data indicate that grazing behavior patterns change based on pasture characteristics and timing of conception. Selection for grazing behavior attributes may be an important tool for selection of cows that are more reproductively punctual.