Climate and environmental effects of nutritional mitigation options to reduce enteric methane in dairy cattle: A life cycle assessment

Abstract

Nutritional mitigation strategies represent an option to reduce enteric methane emissions from ruminants, but these strategies must not have undesirable side effects.Therefore, the present study aimed to analyze the environmental effects of supplementation of typical dairy cow feeding rations in Denmark (S0) with 20 g extra fatty acids per kg dry-matter (S1), 10 g nitrate per kg dry-matter (S2), and 60 mg 3-nitrooxypropanol (3-NOP) per kg dry-matter (S3). A cradle-to-farm gate life cycle assessment approach was used, where fifteen environmental impacts were assessed to capture the environmental effects. Pairwise Monte Carlo simulations were conducted to identify statistically significant results.It was found that the climate impact per kg of milk decreased for all the strategies (−7 % in S1 and S2 and −13 % in S3) compared to S0. Furthermore, lower land use and land use change emissions were determined by the partial replacement of soybean meal with cracked rapeseed (in S1) or nitrate (in S2). The reduction in the level of enteric methane also contributed to decreases in the toxicity-related impacts of organic chemicals in S1. The use of nitrate in S2 also involved a decrease in the use of soybean meal, which contributed to decreases in the land use impacts. In strategies S2 and S3 increases in other environmental impacts were observed compared to S0 because of the manufacturing of nitrate or 3-NOP, or higher N excretion and emission at supplementation with nitrate.It was concluded that S3 was more effective in reducing the climate (and human-toxicity impacts of organic substances) impacts, while S1 caused small decreases in a wider range of environmental impacts. The present study has an important contribution to quantifying a wide range of environmental effects for intensive dairy and regarding the implementation of nutritional strategies in dairy cattle to reduce enteric methane.