Milk yield holds the key to lower carbon footprint

Want to reduce your herd’s carbon footprint? Then the easiest way is to increase milk yields, says Kite Consulting, the publisher of the first authoritative study into the UK’s dairying carbon footprint.

That is because methane production from cows – the main factor in the carbon equation, accounting for about 55% of all carbon output – is not heavily related to yields. A 9000-litre cow produces 125kg of methane a year, equivalent to 2600kg of carbon dioxide (CO2) a 5000-litre cow produces 103kg of methane, equivalent to 2170kg of CO2.

On a weight basis the 9000-litre cows have a CO2 output of 290kg/1000 litres of milk, compared with 5000-litre yielders, with an output of 434kg. More milk a cow would also mean there would need to be fewer cows to achieve a given volume of milk and fewer youngstock. And if cow longevity rose at the same time even fewer replacements would be needed, all of which would further reduce carbon output.

“There could be a virtuous carbon circle operating in the industry,” says one of the Kite co-authors, Tim Davies. “More milk a cow, fewer cows, fewer replacements. The trouble is we know how hard it would be to do that. It is easy to say, but hard to do.”

Many farms would also not wish to move from a low-input, low-output system to a higher output one. But they can still reduce their carbon footprint through dietary, forage and grassland management tactics, he says.

High starch diets of maize, whole-crop or cereals produce less methane, while high-fibre grass silage diets result in greater volumes of methane. Feeding unsaturated oils like soya, rapeseed or fish oils will also help reduce methane production. “But watch out for butterfats if you feed them they could drop.”

The amount of dietary protein also needs to be watched. High protein diets have a higher level of nitrogen and when more nitrogen is excreted more will be lost to the environment as nitrous oxide (N2O) and ammonia.

In the past 20 years the level of protein fed has fallen from 19.5 to 17.5%, but it is feasible to take dietary protein levels even lower, down to 14.5-15% at the extreme without losing any yield. However, such diets are significantly more expensive and require more management.

Feed additives known as ionophores could also potentially be used, subject to their approval by the relevant food safety authorities. These modify rumen fermentation and can reduce methane output by 15%. “We are not allowed to use the main one – monensin – because it is classified as an additive. But researchers are looking at other similarly effective products which may be developed in future from plant extracts.”

The more by-products from the human food industry which are fed to cows, such as brewery, bakery and vegetable oil by products, the lower the carbon footprint of milk production will be, as the carbon footprint of these products is borne largely by the human food production industry. Many of these products if they were not fed to cows would otherwise be destined for landfill, where methane would also be produced as they rotted. That should be offset against dairying’s contribution.

Feeding to ensure replacements calve at 22-24 months will also help, he insists, reducing the carbon footprint of heifer rearing by about 24% compared with calving at 30-34 months. Making the most of muck and slurry and incorporating legumes, such as clover and lucern can also substantially reduce the amount of carbon losses from N2O, which accounts for about 20% of the carbon load.

Low-yielding extensive systems, which naturally have a high carbon output (as methane) in relation to their yields should concentrate on using legumes with muck and slurry to minimise carbon losses.

There is no direct incentive for dairy farmers to reduce their carbon footprint, but there are plenty of incentives to improve technical performance. The beauty is, he says, that achieving the latter will also achieve the former. “The main driver is efficiency. The more efficient a production system is, the less carbon a litre a farm will produce.”

Lessening carbon load

  • Maximise slurry use
  • Higher yields mean less methane
  • Use by-products