Assessment of greenhouse gas emissions in dairy cows fed with five forage systems

Abstract

Thirty Holstein cows were arranged in a randomised block design for 287 days and fed rations of five forage systems: Italian ryegrass in rotation with corn (S1), hybrid ryegrass mixtures with three legumes in rotation with corn (S2) or sorghum (S3), red clover with hybrid (S4), and Perennial (S5) ryegrass pastures. In systems S1, S2, and S3, the cows remained in the barn throughout the study period and were fed total mixed ration (TMR). In systems 4 and 5, the cows grazed in a pasture and were only fed at the barn when grazing was not possible. All rations were balanced with a low quantity of concentrate at a forage/concentrate ration of approximately 80/20. Feed intake, milk quantity, and milk quality test data were entered in the program CAP2’er® to calculate the test-related carbon footprint. Results, based on 287 days trial, expressed as grams of CO2 equivalent per kilogram of fat and protein corrected milk (FPCM), were 724 (S1), 701 (S2), 764 (S3), 507 (S4), and 528 (S5). Actually, the lower results in S4 and S5 than results for S1, S2 and S3 seem more related to the inclusion of the carbon sequestration and land-use change issues than more inputs/more but not enough milk production. When soybean meal is imported, the findings highlight that soybean meal emission factor due to land use change (LUC) strongly affected CO2 equivalent emissions in systems S1, S2 and S3 where 670, 625 and 628 kilograms of soybean meal were consumed by cows in the trial. Highlights The higher productivity of double-cropping systems does not compensate for the higher amount of greenhouse gases that they emit, measured as CO2-equivalent emissions per kilogram of FPCM. Pasture-based systems emit lower quantities of greenhouse gases per kilogram of FPCM, but their milk yield is lower than that of more intensive systems. Emission factors differ considerably due to differences in soil use. The result of greenhouse gas emissions from the system will largely depend on how these emission factors are analysed.