Comparison of greenhouse gas emissions from corn- and barley-based dairy production systems in Eastern Canada

In Canada, corn silage is increasingly fed to lactating dairy cows at the expense of barley silage and other forages, as its high-energy content can improve animal performance. Moreover, corn silage is known to reduce methanogenesis in the rumen compared to barley silage. A life cycle analysis was conducted to compare whole farm total GHG emission and greenhouse gas (GHG) intensity (kilogram CO2-equivalent per kilogram of milk) of corn- (CS) and barley- (BS) based dairy production systems. For this purpose, a virtual farm representative of typical dairy production systems in Quebec was used to simulate the 6-year lifespan of a dairy cow, from calving to culling. Diets fed to lactating cows consisted of 54.4% corn or barley silage, 5.5% grass hay and 40.1% concentrate (dry matter basis). The impact of silage digestibility (measured as total digestible nutrient [TDN] content) on total GHG emissions of the dairy production system was also assessed. From prior experimental data, milk production was assumed to average 34.7 and 31.9kg/day for lactating cows fed corn and barley silages of medium TDN content respectively. Milk production was also assumed to be positively correlated with the TDN content of diets. To compensate for differences in milk production per cow, the number of cows was adjusted to obtain similar total fat- and protein-corrected milk production between farms. Forage (silage and hay) and grain (barley or corn) were cultivated on-farm whereas all other feed ingredients were purchased. Greenhouse gas emissions were estimated with the Holos model using a “cradle-to-farm gate” approach. Methane (enteric fermentation and manure storage), CO2 (farm operations, production and transportation of purchased feed) and N2O (N degradation from crop residue, manure, N leaching and volatilization) emissions were taken into account. Enteric CH4 was predicted from animal energy requirements and diet composition. Percentage of energy intake lost as CH4 was assumed constant regardless of silage TDN content. When silages having medium TDN content were used, total GHG emission was reduced by 13% with CS compared to BS, despite the fact that the reduction of enteric CH4 emissions with corn silage was partially offset by increased CO2 emissions from the additional purchased feed protein sources (+9%). Within a forage type, increasing silage TDN content reduced GHG intensity. Finally, the GHG intensity of dairy production systems was lower with high digestible barley silage compared to low digestible corn silage showing the importance of producing forages with high digestibility that maximize milk production.