The Sheep Project: Helping Us Understand Wool Production in the Past
Research by Historic England Zooarchaeologists is investigating how we can detect evidence for wool production from archaeological sheep bones and teeth. The wool industry was a key driver of the medieval and post-medieval economies in England. Various farming methods have been used to improve the quantity and quality of wool, including sheep breeds, part of the fleece used, and feeding regimes. Traditionally, sheep were often castrated to enhance the quality of wool.
Zooarchaeological evidence for wool production
In assemblages of archaeological animal bones we see evidence for intensification of wool production from the medieval and early post-medieval periods, through increasing use of adult sheep and high proportions of males. However the identification of castrated animals (called wethers) is problematic.
Developing a research collection
In order to improve methods for identifying wethers in archaeological assemblages and to investigate other aspects of sheep management in the past, we are studying a large collection of sheep (Ovis aries) skeletons with known life history. The sheep are of the unimproved Shetland breed, chosen because it is one of the smallest British breeds of sheep and is thought to closely resemble prehistoric and early historic animals. The exact age (in days), sex (female, male or wether), and quality of nutrition were recorded in detail, allowing us to explore the effects of each factor on the size, shape, and growth of bones and teeth.
Identifying sheep management
In line with previous studies we have shown that the size and shape of bones can vary between sexes. For example, some bones of wethers are longer and more slender than those of rams. Our research has shown that the shape of part of the pelvis (hip) joint allows complete separation between rams and ewes, while wether pelves are intermediate – the potential blurring of shape distributions may therefore indicate the presence of wethers.
Bone growth is also affected by castration, particularly in the process of epiphyseal fusion, the joining of bone ends or articulations with the central shaft of limb bones. Our study shows that fusion is severely delayed in wethers, compared to ewes and rams. In contrast, teeth show a different growth pattern, erupting at about the same time in all three, but generally wearing down faster in rams and wethers as they get older.
Comparing bone fusion and tooth data is a possible tool for studying the composition of archaeological sheep flocks, with high proportions of unfused bones (from seemingly young animals) along with heavily worn teeth (of older animals) indicating the presence of wethers.
We are currently studying these patterns in archived data and collections to see if the pattern is similar in other breeds and regions, and might therefore be applicable to a wide variety of archaeological assemblages.
In addition to the research by HE specialists, many external researchers use our sheep collection. Isotope analysis, analysis of biochemical signatures in animal tissues relating to environment, diet and geographical origin, has been applied to wool and bone samples helping us to understand how and why these signatures vary between and within flocks. This will assist us in studying husbandry and movement of sheep populations as well as production and trade in artefacts of bone, horn and wool.
Davis, SJM, ‘The effect of castration and age on the development of the Shetland sheep skeleton and a metric comparison between bones of males, females and castrates’, Journal of Archaeological Science, 27 (2000), 373–390
Holmes, M, ‘Southern England: A review of animal remains from Saxon, medieval and post medieval archaeological sites’ (HE Project 6145, forthcoming)
von Holstein, I C C, Hamilton, J, Craig, O E, Newton, J and Collins, M J, ‘Comparison of isotopic variability in proteinaceous tissues of a domesticated herbivore: a baseline for zooarchaeological investigation’, Rapid Communications Mass Spectrometry, 27 (2013), 2601–2615 doi: 10.1002/rcm.6725
Popkin, P, Baker, P,Worley, F, Payne, S, Hammon, A, ‘The Sheep Project (1): determining skeletal growth, timing of epiphyseal fusion and morphometric variation in unimproved Shetland sheep of known age, sex, castration status and nutrition’, Journal of Archaeological Science, 39 (2012), 1775–1792
Worley, F, Baker, P, Popkin, P, Hammon, A and Payne, S ‘The Sheep Project (2): The effects of plane of nutrition, castration and the timing of first breeding in ewes on dental eruption and wear in unimproved Shetland sheep’, Journal of Archaeological Science Reports, 6 (2016), 862-874
Polydora Baker is Senior Zooarchaeologist at Historic England. She is a co-founder of the Professional Zooarchaeology Group (PZG) and has recently published Animal Bones and Archaeology: Guidelines for Best Practice, with co-author Fay Worley and many external colleagues. She is continuing research into sheep husbandry based on modern and archaeological skeletal collections.