Distribution of Salers cows in contrasting rangeland pastures relative to established slope and water guidelines

Abstract

Topographical constraints, particularly steep slopes and far distances to water, have persistently challenged livestock distribution globally. Information gained from global positioning system (GPS) tracking devices have accelerated knowledge of cattle (Bos taurus) use of complex topography to potentially challenge established guidelines. In northern Wyoming, USA, we deployed 5 GPS collars on multiparous Salers cows with calves from July to November 2018–2019. Cattle rotated between 2 contrasting rangeland pastures: the Basin pasture (Foothills Shrublands and Low Mountains ecoregion; mean slope of 17.7% (range: 0.87–111.01%)) and Mountain pasture (transitioning to Absaroka-Gallatin Volcanic Mountain ecoregion; mean slope of 24.4% (range: 0.26–125.11%)). We estimated mean and maximum slope use and distances from water, along with daily distances traveled for each GPS-collared cow per pasture per year. We also generated utilization distributions with Brownian bridge movement models to compare mean slope and distances to water among quartiles of predicted use, and compared stocking rate adjustments per pasture between standard and GPS location derived methods. Mean daily distance traveled was 5126.5 km and 5011.6 km in the Basin and Mountain pastures, respectively, and average distance to water was <1.65 km. Cattle use was concentrated on gentler slopes than the average slope of the pasture. Mean and maximum slope use was 17.5% (9.9°) and 68.2% (34.3°) respectively in the Basin pasture and 8.9% (5.1°) and 57.1% (29.7°) in the Basin pasture. Compared to standard methods, GPS-derived grazeable area calculations suggested that there was less grazeable area in the Basin pasture but more in the Mountain pasture. Our results indicate that cattle adapted to mountainous terrain may challenge established guidelines for slope use, but not for distance to water. Such information could influence grazeable area calculations, stocking rates, and water development.