What research has been done so far?
Since 2003, scientists researching low greenhouse gas forages have receivedfunding from the Pastoral Greenhouse Gas Research Consortium (PGgRc), theNew Zealand Agricultural Greenhouse Gas Research Centre (NZAGRC) andthe Ministry for Primary Industries’ (MPI) Sustainable Land Managementand Climate Change (SLMACC) fund. The aim is to establish whether dietarymanipulation can provide a practical and cost effective route for reducingemissions of methane and nitrous oxide.
Pasture is the dominant feed for New Zealand ruminants and hence the largest focus in New Zealand has been on measuring emissions from pasture-fed animals. The primary focus of this work has been to establish baseline emissions from pasture-fed animals and to test whether manipulating quality (e.g. digestibility, fibre) can reduce emissions. An element of the work has been to examine the influence ofspecific chemical constituents (e.g. elevated sugar content) on methane and nitrous oxide emissions.
Work has also been undertaken to examine alternative forages and non-pasture feed options and test whether their incorporation into pasture diets results in a reduction in emissions below those of pasture-only diets.
The majority of work has been carried out using sheep – a consequence of cost, practicality and availability of equipment – although some work with cattle has been undertaken. Prior to 2009, methane emissions were mostly measured using the sulphur hexafluoride (SF6) tracer technique. This technique measures emissions from free-ranging animals by sampling exhaled breath in containers placed around the neck of the animal. Since 2009, emissions have been measured almostexclusively in respiration chambers. In these chambers animals are enclosed for 48 hours and exhausted air enriched with methane from exhaled breath is sampled and compared with non-methane enriched ambient air to determine the quantity of methane produced. This is considered to be the standard method for estimating methane emissions from animals as the environment can be controlled, feed intakemonitored accurately and measurements made in a stable and reliable manner.
To read more on the substantial work undertaken in this area, download the NZAGRC-PGgRc Low Greenhouse Gas emitting feeds factsheet or review the journal articles and science reports below.
What have we found?
Broad conclusions
There are a number of broad conclusions that can be drawn from the work already completed in addition to specific conclusions from research streams:
1. Enteric methane emissions are generally stable when expressed on a unit of intake basis.
2. It takes large changes in diet to bring about changes in enteric methane  emissions.
3. Predicting emissions based on chemical analysis is highly problematic. For example, chicory and forage rape are similar in quality but chicory appears to have no influence on methane emissions while forage rape does.
4. Even where emissions are shown to be reduced (e.g. forage rape), the overall impact at the national scale will be small because the alternative feed makes up a minor component of the overall diet. 
5. Although there is no direct link between feed quality and lower emissions at a plant level, continuing to use high quality feed can lower a farm systems’ emissions intensity (emissions per unit of product). 
To read more on specific research findings, download a copy of the NZAGRC-PGgRc Low Greenhouse Gas emitting feeds factsheet
What next?
Current and future research
Many different crops have been analysed and, while showing promise in some areas, there are no definitive, easy or dramatic ways to reduce emissions of pasture basedlivestock by diet alone. 
More work is needed to assess the overall emissions impact of feed options. Individual gases can not be considered in isolation.
While reducing nitrogen losses is an immediate priority for many farmers, lower nitrogen intake may in turn lead to higher methane emissions. For example, maize silage has lower nitrogen content but can be of lower quality than other feed options so an animal needs to eat more to achieve optimal performance. Thus, reductions in nitrous oxide are likely to be partially offset by increases in methane emissions.
Current research priorities include undertaking a comprehensive evaluation of the nitrous oxide emissions associated with grazing forage rape and other work to fill in knowledge gaps, and undertaking thorough assessments of promising options such as plantain. Work with plantain is being extended to comprehensively study its impacts on nitrogen partitioning, methane and nitrous oxide emissions, and soil carbon stocks.