418 GNSS tracking to assess site selection of calving cows in relation to herdmates.

Abstract Real-time detection of calving is critical for proper reproduction management, as it may allow for assistance with dystocia and/or prevention of peripartum mortality. GNSS tracking has been used to monitor the ethological changes associated with calving in free-ranging cows, allowing its automatic detection (García García et al., 2023). A complementary approach to GNSS tracking is to identify patterns of calving site selection, which may allow the identification of areas where calving cows are most likely to be found. The aim of this study was to identify common patterns in the characteristics of the sites selected by cows during calving in relation to the sites selected by non-calving herdmates. Thirty-four cows from three farms were fitted with commercial GNSS collars (Digitanimal Ltd.) during the peripartum period. Calving sites were defined as the GNSS coordinates of cows on the day of calving while isolated from herdmates. Grazing land within each paddock was classified according to distance to water (< 25 m, 25-100 m, and >100 m), geomorphology (Jasiewicz and Stepinski, 2013) and canopy cover (< 10%, 10-20%, 20-40% and >40%) using digital elevation models and orthophotographs. For each land category, Jacobs’ selection indices (JSI) were calculated from the GNSS positions. The difference between the JSI of the calving cow and the JSI of her herdmates during the same period was used as an indicator of site preference (positive values) or rejection (negative values). Data processing and calculations were carried out using the open-source software R. Calving cows showed a greater preference for areas further away from water sources (> 100 m) than their herdmates on the three farms (JSI difference between +0.24 and +0.77). Conversely, they rejected areas close to water (25 to 100 m), with JSI differences ranging from -0.24 to -0.98. Regarding geomorphology, differences between calving cows and their herdmates were not consistent between farms for most geomorphons. On all farms, cows selected gentle slopes (5 - 10%) for calving, but herdmates also preferred this geomorphon in two farms and rejected it on one farm, resulting in JSI differences between -0.19 and +0.25. Systematic differences were only observed for flat areas (JSI differences between -0.07 and -0.33). In terms of tree cover, calving cows showed a relative preference for areas with more than 40% canopy, with JSI differences ranging from + 0.04 to +1.04. Despite the differences between farms, which may be due to paddock size and spatial configuration, some common behavioral patterns were observed. Calving cows avoided areas close to water, flat areas, and areas with little or no canopy cover, which can be interpreted as an avoidance of cattle concentrations and exposed areas. These results may facilitate the location of calving cows on heterogeneous pastures.