To challenge the argument that sheep are irredeemably bad for the environment RBST has been running a project looking at the carbon content of wool and the extent to which sheep have the potential to be a carbon sink.  Conservation adviser Andrea Parry-Jones reports on the study findings:

Historically, UK sheep breeds have had a significant economic, environmental and cultural impact – in fact, this country was built on the wealth generated by the wool trade.  Over recent times, however, wool has become less popular and increasingly the practice of farming the sheep that produce it has been viewed in a negative light in terms of its contribution to climate change.  Although the data are complicated and incomplete, RBST recognises that there is a significant issue with the perception of the effect of greenhouse gases (GHG) from sheep farming, so this study was designed to help fill that data gap by looking at the carbon content of wool. 

Lamb production systems are association with three main GHGs: 

1. -        Methane produced as a by-product of digestion via enteric fermentation and manure management processes.
2. -        Nitrogen oxide, emitted from soil following nitrogen fertiliser and manure application (urine and dung deposited on grasslands).
3. -        Carbon dioxide from energy use on farm and during production of animal feeds.

In fact, all livestock is associated with GHG production but it is important to state from the outset that, with sheep, this is a density, not a species, issue.

We have 83 breeds of sheep in the UK, breeds that have evolved and adapted to widely varying locations and environments and which have their own individual traits.  It is important, therefore, that any study of their impacts needs to acknowledge this diversity.  What we wanted to discover was how much carbon is carried by the wool from these diverse breeds, so an essential element of the study was to harvest wool from as many of those breeds as possible.  The majority were longwool breeds, as these are the breeds that carry the most amount of wool – a Lincoln Longwool could, for example, carry up to 14kg of fleece.  We harvested wool from different breeds, different flocks and different farming systems across the UK.  We also included samples from sheep of different ages and of both sexes and, with those breeds with colour variations, we also looked at samples of different colours. Here we have to thank the very many sheep breeders across the country who sent in wool samples.

The initial findings have revealed that diet, age and habitat have a greater influence on carbon, nitrogen or hydrogen storage than breed.  What makes the real difference is the farming system and the way in which the sheep are kept. 

Breeds themselves have their own parameters;  for example the Greyface Dartmoor, which has a very hair-like fleece has a lower percentage of carbon but a higher percentage of hydrogen than something like the Leicester Longwool.

We’ve seen sheep that have come back with over 50% carbon in their fleece and these are sheep that have been kept in the most natural, extensive systems.  And while you might think that a Leicester Longwool might not be at home on the top of a hill, the flock identified with the highest carbon readings is from Wales and is kept organically and extensively with minimal use of antibiotics and anti-parasitics on land that is regeneratively farmed. 

What we also found was that sheep that are farmed in the way that they have been traditionally adapted to, such as Herdwicks and Gritstones kept extensively on moorland where they have a varied natural diet, have very high percentages of both carbon and nitrogen. 

Coastal animals and animals on pasture with a very high legume content have a high nitrogen content. 

Very interestingly, we found that those animals that are farmed more intensively and those that are kept for showing have a higher hydrogen content which suggests that there is excess hydrogen present in those animals’ diets. 

From looking at the animals in the study, it appears that the weight of the animal doesn’t make a massive difference, nor does the sex. 

Carbon storage within the fleece does vary between individuals; for example we took samples from an entire flock in one location that grazed the same pasture with different age ranges and saw a variance of up to 6% and it was the where the sequestration was declining in the older animals. 

In contrast, at another location with the with animals on the same pasture and of the same age range were all within about 0.2% of each other. 

We also sampled animals from slightly more unusual habitats, including salt marshes.  Those animals showed very good quality wool, indicating a good quality animal with good carbon storage.  In the sampling we even had animals of up to 16 to 17 years old, a stage when most would be long gone, and while none of them had a particularly high carbon storage but they were storing plenty of hydrogen and nitrogen which indicates that those fleeces can be used to improve soil structure or in gardening applications.

We have sampled some commercials and some composite breeds and what we did find was that they do have a lower hydrogen content but not a particularly high carbon content and none of those samples came back at higher than 44%. 

Overall, what we believe this study shows is that if farmed extensively, in systems that reflect the environments they have evolved for, our native breed sheep can play their part in carbon sequestration through their fleeces.  Sheep and their wool are part of the natural cycle and one of wool’s greatest properties as a sustainable material is that it is biodegradable and so capable of ultimately returning the carbon it stores to the soil.  Sheep do have the potential to be a carbon sink, particularly if the wool they produce is put to good use once off the sheep.

Project summary

The overall aim of this project was to investigate the quality of wool samples according to composition of carbon, nitrogen and hydrogen isotopes. The study was focused on elemental analysis of wool samples from the following breeds: 

1. Whiteface Dartmoor
2. Devon and Cornwall Longwool
3. Greyface Dartmoor
4. Cotswold
5. Lincoln Longwool
6. Wensleydale
7. Border Leicester
8. North Ronaldsay
9. Leicester Longwool
10. Portland
11. Balwen
12. Suffolk
13. Herdwick
14. Teeswater
15. Gritstone
16. Badger
17. Icelandic, and others. 

Wool consists of carbon, nitrogen, hydrogen, sulphur and other elements and minerals. One of the most important parameters to investigate in the quality of wool was the carbon/nitrogen ratio that is also influenced by different factors. Alongside the diet, age and habitats, isotopes could vary seasonally. For instance, high content of carbon (C) was found in summer wool, whereas high nitrogen (N) was prevalent during the winter/autumn. Moreover, the content of hydrogen (H) was found to be higher in the summer.

Approximately 10 mg of each wool sample was weighed and underwent elemental analysis for carbon, nitrogen and hydrogen content. The wool composition was presented across and within the breeds.

According to the measurements, the ranges for carbon, nitrogen and hydrogen across all breeds in average were 44.3%-48.5%, 12.07%-14.2%; 6.3%-7.3%, respectively.

Total percentage of all three elements: carbon, nitrogen and hydrogen were in range between 63% and 69%.

Badger showed 64% of total carbon, nitrogen, hydrogen, whilst Herdwick had 68.86%.

Carbon/nitrogen ratio was in a range between 3.29 (Cotswold) and 3.68 (Balwen, Herdwick).

Data on wool composition of each individual sample within the breeds are also presented and described in the report.

 

 Picture : Charlie Dodds