High yielding ryegrasses with increased water-soluble carbohydrate (sugar) levels could help cut greenhouse gas emissions and reduce nitrate pollution alongside their potential to improve output from grassland.
According to Pete Wilkins, head of grass breeding at the Institute of Grassland and Environmental Research (IGER), the improved protein-energy balance in high sugar grasses – which is the key to better livestock performance – is also the reason for significant environmental bonuses.
While further animal research is required to quantify the potential to reduce methane emissions, there is no doubt in Dr Wilkins’ mind the already proven effect of improved nitrogen use will result in reduced waste going into the environment.
“Cattle and sheep are poor converters of grass protein into milk and meat, with only about 20% typically being used and the rest being wasted in faeces and urine,” he explains. “Some of this is recycled by grass, but the greater proportion will be leached away as nitrates or volatilised into the atmosphere as nitrous oxide – one of the main greenhouse gases.
“A major reason for these losses is the imbalance between readily available energy and protein within grass. Proteins are rapidly broken down when feed enters the rumen. However, when the diet lacks readily available energy, the rumen microbes can use less of the nitrogen released from the feed, so much of it is absorbed as ammonia and eventually excreted.
“High-sugar grasses bred at IGER are a better source of readily available energy and, therefore, allow the rumen microbes to process more of the grass protein. Research has shown this can result in more than 10% more of the protein being used for production and hence we see higher milk yields and improved liveweight gains from these ryegrasses. When more is used for production, less is wasted, so ultimately we see the added environmental benefit.”
The IGER grass breeding programme responsible for high-sugar grasses has been ongoing for more than 25 years and is now beginning to bear fruit. The first benchmark high sugar grass variety was the diploid intermediate perennial AberDart, which first became commercially available in 1999, but water-soluble carbohydrate levels are significantly higher in subsequent varieties such as AberStar and will be higher again in varieties like Aber- Magic, still in National List trials.
“We could see even higher sugar levels in future varieties, but the challenge going forward is ensuring this is not at the expense of key criteria such as yield and persistency,” adds Dr Wilkins.
Increasing interest in the environmental impact of modern agriculture – and not least that of the livestock and grassland sectors – looks set to keep future research on high sugar grasses in the spotlight. The recently announced DEFRA research project to look into how dietary changes can affect methane emissions from ruminants may well be an important watershed.
“Methane is one of the more potent greenhouse gases and agriculture is responsible for about 36% of emissions in this country,” continues Dr Wilkins. “So if we can show a reduction in methane alongside the nitrogenous waste products such as nitrous oxide and nitrates this will greatly strengthen the environmental position for high sugar grasses.
“At the moment we only have lab work to back up the theory that methane emissions are reduced when high sugar grasses are fed. If future research goes ahead as planned, we should soon have quantifiable evidence of reduced methane emissions in the live ruminant animal.”