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Practical and sustainable considerations for the mitigation of methane emissions in the northern Australian beef herd using nitrate supplements
The efficacy of methane reduction, animal productivity and risk of nitrite toxicity were examined when Bos indicus cattle consuming low quality tropical forages were fed nitrate to correct a deficiency of rumen degradable nitrogen (RDN). The main findings of this project were:
- Dry matter intake and liveweight gain responses for steers were similar when urea or nitrate salts are fed at isonitrogenous rates.
- There was no significant reduction on daily methane production (g CH4/d) for individual steers weighing 400 kg when dosed with nitrate up to a rate of 50 g daily (7.9 g nitrate/kg DM), but reductions in methane yield (g CH4/kg DMI) can be achieved.
- Nitrate supplementation was consistently associated with increased blood methaemoglobin concentrations and suggests an elevated risk of nitrite toxicity.
- Concentrations of blood methaemoglobin reported in this project are higher than other published studies despite using low dietary nitrate concentrations. This project has confirmed that feeding frequency effects have an important role in the development of methaemoglobinaemia.
- A significant respiratory challenge was evident when nitrate supplemented cattle were subjected to exercise.
- The use of nitrate blocks in a grazing trial resulted in lower consumption by cattle compared with urea lick blocks. Cattle consumed insufficient N from nitrate to remedy the underlying deficiency of RDN. This resulted in a lower liveweight response, a reduction in BCS and no impact on daily methane production. Blood methaemoglobin concentrations increased in a dose respondent manner.
Caution should be exercised when feeding nitrate salts as a urea substitute in self-fed supplements to extensively managed beef cattle herds during the dry season. Nitrate consumption is unlikely to reach a level that significantly decreases methane production, or, if this threshold is achieved, there is significant risk of nitrite toxicity. The existing methodology for reducing greenhouse gas emissions by feeding nitrate to beef cattle was approved prior to the findings of this project being released. It is suggested that the methodology and underlying technical assumptions be reviewed using the findings from this project, which contains data specific to the forages, supplements and feeding practices relevant to the northern Australia beef cattle industry.
Future research on the use of nitrate in the context of northern Australian beef cattle industry should focus on mechanisms to minimise the risk of nitrite toxicity, thereby allowing greater levels of nitrate to be safely fed and thereby achieve a reduction in methane production.
This page was last updated on 25/07/2017
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