Influences on calf productivity during five decades of cow-calf grazing of northern prairie

Abstract

Understanding calf weight gains from grazing rangeland ecosystems requires long-term data to disentangle influences of biophysical and animal factors, and management. However, long-term experiments with consistent management treatments with livestock weight gain data are scarce. To address this gap, we analyzed a legacy dataset of grazing during the growing season (June-September) in native northern mixed-grass prairie of the North American Great Plains that included individual on– and off-pasture weights of Hereford (1975–2001) and crossbreed (2003–2021) cows and calves grazing from June to September, spanning 47 years near Cheyenne, Wyoming. We used regression tree analyses to evaluate the influences of biophysical (forage production estimated via NDVI LANDSAT time series, temperature, and precipitation) and individual animal factors (breed (Hereford from 1975 to 2001 and crossbred from 2003 to 2021), cow age, cow BW, and calf gender), and management (stocking rate, Animal Unit Days per hectare), on individual calf weight gain. We observed a positive temperature trend and a negative precipitation trend over the five decades. Forage production was positively associated with precipitation and negatively with temperature. Breed (Hereford vs crossbred) was the most important factor for calf weight gain, followed by stocking rate, temperature, cow weight, precipitation, cow age, forage production and calf gender, with the fitted model explaining 64% of the variation in calf weight gain. Calves from crossbred cows gained 26% more than calves from Hereford cows (1.2 vs 0.88 kg/head per day). Our findings from nearly five decades of grazing research offer key insights for beef production responses from native, northern mixed-grass prairie rangeland ecosystems. First, crossbreeding offers advantages to calf weight gain. Second, the importance of stocking rate and cow BW on calf weight gain, along with observed trends of precipitation and temperature influencing forage production, underscores the need for more flexible management for sustainable beef production. Third, over the five decades of this experiment, factors influencing individual productivity have shifted from variables associated with the selection of the animal biotype and stocking rate to primarily climatic factors. The shift from management-driven factors to more variable climate-driven influences reflects the need for adaptive grazing management —a structured approach that involves planning, monitoring, and adjusting strategies in response to environmental variability.