As a sector, agriculture is the highest emitter of greenhouse gases in Ireland.

There is a strong correlation between water soluble carbohydrates (WSC) and dry matter digestibility (DMD) on the Department of Agriculture Recommended List.

Varieties with high WSC provide extra energy (sugar) for the rumen microbes, which allows the animal to utilise more of the available protein from grass and clover.

The proportion of this protein used for meat or milk production is increased, and the amount lost via excretion is reduced.

There is some evidence that higher quality grasses (in DMD terms) have the potential to reduce methane emissions.

Work on comparing high and low pre-grazing yields from Teagasc identified reduced emissions with the low pre-grazing yields.This was apportioned to the increase in quality of the lower pre-grazing yields.

In a study conducted at Moorepark comparing a total mixed ration (TMR) diet to a grass only diet, methane emissions were higher for the TMR group than the grass group (397 v 251 g/cow per day). The TMR group also emitted more methane/kg of fat and protein (200 v 174 g/kg) than the grass group.

They also emitted more methane/kg of dry matter intake (DMI) (20.28 vs. 18.06 g/kg of DMI) than did the grass group.

In this study conducted with spring-calving cows who consumed a high-quality perennial ryegrass diet in the spring, the cows produced less enteric methane emissions per cow, per unit of intake, and per unit of fat and protein than cows offered a standard TMR diet.

There is widespread evidence as to the benefits of higher quality grasses – in terms of animal intake and animal performance.

We can also say that this benefit extends to the environment too. Looking at the Recommended List, there is a marked difference between the best grass variety in terms of DMD (Abergain, 85.8% DMD) and the worst (Boyne, 82.3% DMD).

These quality parameters are fed into the Pasture Profit Index, so picking varieties that rank highly on the PPI and on the on-farm variety evaluations is important for reducing greenhouse gas emissions.

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Grass varieties impact on methane emissions

The debate on climate change and agriculture tends to focus on methane emissions. Aidan Brennan looks at research which shows that high DMD grass diets can reduce methane emissions.