51. Modeling Drought-related Changes in Forage Yield and Quality and Its Impacts on Whole-farm Greenhouse Gas Emissions in Canadian Cow-calf Production Systems.

Abstract Feed management in Canada’s cow-calf sector is mainly characterized by summer pasture grazing and winter feeding of preserved forages. Extreme weather events, including increased frequency of drought associated with climate change, are expected to affect forage yield and quality and therefore, impact whole-farm greenhouse gas (GHG) emissions. Using the Holos whole-farm model, net farm GHG emission intensity (kg CO₂e kg beef-1 marketed as weaned calves and cull cows) was calculated for an average farm in Manitoba. The baseline farm scenario was comprised 156 cow-calf pairs and 7 bulls utilizing summer grazing, extended bale grazing during the fall and early winter, and confinement feeding of preserved forages during winter. Scenarios included a drought-induced 8% decrease in forage yield (Scenario 1) and a 40% decrease in yield, which resulted in an increase in crude protein from 10.2 to 16.5% dry matter (DM) and a decrease in neutral detergent fiber from 60.0 to 54.7% DM (Scenario 2). Furthermore, two producer response scenarios were modeled to reflect the decisions made by producers in response to reduced forage yields: i) reduction in herd size, and ii) feeding purchased supplemental hay on pasture. Compared to the baseline farm, GHG emission intensity decreased both in Scenario 1 (17%) and Scenario 2 (35%), when the herd size was reduced in response to drought. Conversely, provision of supplemental hay on pasture in response to drought increased farm emissions intensity both in Scenario 1 (2%) and 2 (14%). Overall, the reduction in forage yield (by 8% and 40%) associated with drought decreased emissions intensity when herd size was reduced/readjusted and increased when purchased supplemental feed was provided. Further work is in progress to examine GHG emissions associated with decreased water quality, as well as a multi-year response to successive drought events. This work quantifies greenhouse gas emissions in Canadian cow-calf systems and examines the impact of drought-related changes in forage yield and quality, as well as water quality on whole-farm GHG emissions intensity, informing programs and policies to support a resilient beef industry.