Analysis of data from 100 dairy farms across five different countries in western Europe has found that fully housed indoor systems tend to have higher carbon footprints.

The research was part of the Dairy 4 Future project and each of the farms, which included participants from the UK and Ireland, was classified as either grazing, indoors, or mixed.

Grazing farms had cows at grass for at least 60% of the time, indoor farms never had cows at grass, and mixed farms grazed for less than 60% of the time.

Carbon footprint was expressed as kg of carbon dioxide equivalent per kg of milk and the housed systems had the highest average figure of 1.51. It compares to 1.14 for grazing and 1.23 for mixed.

Marion Sorley from Teagasc said the contributing factors that make up a farm’s carbon footprint differed significantly for housed systems compared to the other two types.

“With the housed systems, generally as your carbon footprint increases, your emissions from manure and concentrates also increases,” she said.

With mixed and grazing systems, trends are less clear, although enteric fermentation (methane), manure, fertiliser and concentrates were key contributors to carbon footprints.

Sorley pointed out that the type of concentrates fed also influenced the figures considerably.

There were examples of imported soya-based feed having a much higher carbon footprint than low crude protein concentrates made from locally grown crops.

Feed efficiency

The researchers found a “strong relationship” between feed efficiency and carbon footprint across all three dairying systems. Feed efficiency is defined as the amount of milk produced per kg of dry matter intake, and it is strongly influenced by the likes of fertility and health.

Sorley said that within grazing and mixed systems, the more time cows spent at grass, the lower the farm’s carbon footprint.

“Improving your milk yield per cow will also reduce your carbon footprint. However, interestingly enough, we only saw this trend with the housed systems. We didn’t really see this with the grazing or mixed systems,” she said.