Work on fodder beet is ongoing, and is also showing promise. One recent study in which sheep were fed 90 per cent fodder beet and 10 per cent grass, up to 50 per cent methane emission reductions were recorded.
"Unlike high cereal diets, where you need at least 80 per cent [of the animal's intake] to be high cereal, you don't need that with fodder beet and forage rape. Understanding that mechanism is where we are currently doing a lot of searching."
Overseas, substituting maize silage for grass silage had yielded 15 per centmethane reductions "but we haven't been getting that here. Again, it's a mechanistic understanding of that we're seeking," Dr Hammond said.
Plants with tannins (eg. birdsfoot, trefoil, sulla) can reduce methane, "but go beyond 4-6 per cent plant tannin content and you start to get palatability issues, affecting food intake". Anything that affects animal performance is relegated down the study options.
Breeding
After thousands of measurements on sheep, researchers have been able to achieve a 10 per cent reduction in methane emissions between high and low emitting breed variants.
The difference can be repeated under varying diets (Lucerne pellets vs pasture), at different times of the year. The characteristics show high heritability (able to be passed on to progeny, so it's able to be used as a selection tool).
The difference between the high and low emitting sheep is that the low emitters have a smaller rumen. They even have slightly higher wool growth. Preliminary economic analysis shows because they have a smaller rumen, their carcass yield is greater. A researcher specialising in breeding, said details of the low-emitting sheep are now available.
Breeding
Dr Hammond said thousands of potential inhibitors (substances that have an effect on methanogens, the microbes that take up hydrogen and carbon dioxide in the rumen for their energy, and produce methane as a byproduct) have now been screened in the lab in an artificial rumen. Those with potential have been rolled out in trials.
Nine substances showing particular potential have now been narrowed to four, and these can inhibit methane production by up to 30 per cent without affecting animal production values.
"So it's quite a promising line of inquiry."
Implementation trials continue, and there will need to be stringent tests to ensure any residues are not going to enter the human food chain. So if compounds prove successful, they're still 5-7 years from roll-out.
Methane vaccines
Vaccines (raising antibodies that will affect methanogens) are the Holy Grail for researchers because in all likelihood the right vaccines will be successful for all animals, in all farm systems, won't leave a residue and can be easily delivered to the rumen via saliva (ie. introduced via the animal's mouth).
The world has been screening numerous options, and now they're also down to the four most promising. The rumen is "a hostile environment", so work continues to find the antibodies that are effective and long-lasting.
Dr Hammond said many more questions remain. What effect does a vaccine have on excreta (and thus nitrous oxide)? Productivity? Product quality?
Once again, the best estimate is that it will be 5-7 years before any vaccine is available for use.
An audience member asked why so much of the research seemed to be with sheep rather than cattle. The explanation is that animal trials are expensive to run, and while AgResearch has state-of-the-art respiration chambers for testing emissions, there are 24 for sheep and only four for cattle. Sheep are smaller and easier to handle.
However, results so far in sheep are being replicated with cattle, and trials with cattle are being ramped up.
