Strategic science of nitrate as a mitigation technology for grazing ruminants

Summary

Supplementary nitrate is effective in reducing enteric methane emission from ruminants in a reliable and quantifiable manner. This project has addressed the process of nitrate metabolism in the rumen and of metabolism of nitrite and methaemoglobin in the animal. Nitrite accumulation in the rumen is best managed through controlled delivery of nitrate (by frequency of consumption or potentially by controlled rate of release within the rumen) and matching of nitrate and feed/substrate consumption to prevent nitrite accumulation in the rumen. Manipulating the rumen environment by a probiotic or by sulphur and molybdenum balance did not control methaemoglobin formation in sheep and therefore did not mitigate risk from nitrite poisoning.

Between-animal variation in metabolism of nitrate (as judged by methaemoglobin levels) is apparent and may offer opportunity for selecting resistant or resilient animals and identifying a rumen microbiology that could be introduced to provide protection. Use of 'slow release' nitrate sources needs to be tested.

Nitrate feeding through lick-blocks for sheep and cattle as well as via liquid supplements and total mixed rations was conducted safely and lick-block demonstrations are currently operating via Action on The Ground projects. Recommendations for best management feeding practises for nitrate were developed in association with another project.