Natural capital to nourishment: The role of dairy in the Scottish food system

JOHN NEWBOLD, PROFESSOR OF DAIRY NUTRITION, SRUC

Circular economies (in which resources are reused and recycled as much as possible) are sustainable economies, and this is as true for food production as for any other industry.

The contribution of dairy to the circularity of the Scottish food system is an all-too-well-kept secret, and one that should be recognised and valued in public discourse and policy debate.

Livestock will continue to be part of future food systems, if those livestock do not compete with humans for food and if the rearing of livestock does not compete with other food production systems for land.

With a mild, moist climate and large areas of land with soil and topography unsuitable for crop cultivation, it’s no surprise that grasslands dominate much of the Scottish countryside. As a result, there is a rich tradition and heritage of expertise in the use of the dairy cow to convert those grasslands into high value food.

The cow is one of nature’s up-cyclers. They convert the cell walls of grass and other plants (comprising cellulose, hemicellulose and lignin) - that are largely indigestible to monogastric animals such as humans – into a highly nutritious and delicious food in the form of milk. Indeed, milk protein scores higher than almost any other food in the Food and Agriculture Organization’s preferred metric of food protein quality, due to its high digestibility and amino acid profile.

This ability to upcycle resources we cannot eat directly is captured in the circularity metric ‘human-edible feed efficiency’. For protein, this is defined as the amount of human edible protein (adjusted for protein quality) produced by a livestock farming enterprise divided by the amount of human edible protein those livestock consume. Dairy cows generally produce more than twice as much human-edible protein as they consume, with this figure being higher for high-forage production systems, such as those practiced in Scotland.

A recent evaluation of the circularity of food production in Ireland (an environment not dissimilar to our own) calculated the amount of food that could be produced per hectare, from a range of feasible crop-only and mixed crop/livestock farming systems. This was to address the question of whether that land should be used exclusively to grow crops for direct human consumption (e.g., cereals, beans and potatoes) or whether more, higher quality food could be produced by integrating livestock. By allowing food production from land suitable for grassland but unsuitable for arable crops, the integration of a dairy-beef system made the whole food system more efficient and more circular.

Circularity is a powerful and compelling argument for a continued leading role for dairy farming in the nation’s food system.

However, there are some tricky trade-offs. In general, ruminant diets rich in plant cell walls (inedible to humans) will generate high yields of methane when digested in the rumen. Substituting some of those plant cell walls with starch or fat will help to push methane down, but if that starch and fat comes from feeds we could use as food (e.g., cereal grains), this will make the dairy system less circular.

The way out of this dilemma is to base ruminant diets on forages (rich in human-inedible plant cell walls), supplemented by non-human edible food processing co-products (such as the traditional use of brewers’ and distillers’ grains, and sugar beet pulp) or former foodstuffs such as bread, bakery products and confectionery. The residual oil and readily-fermentable carbohydrates in food industry co-products are strategically important in realising high rates of milk production – with lower emissions of methane - in cows offered forage-based diets.

This then highlights another challenge. Is it more circular to use those human-inedible resources as feed or as fuel (i.e., in anaerobic digesters)?

This becomes a question of politics and economics, but this debate is incomplete and always partial unless proper value is placed on the nutritional quality of different foods in the nation’s diet (which would highlight the value of dairy) and, of course, the circularity of the systems in which they are produced.

Get in touch: john.newbold@sruc.ac.uk