Comparison of isotopic variability in proteinaceous tissues of a domesticated herbivore: A baseline for zooarchaeological investigation

RATIONALE A variety of metabolic, dietary and climatic influences on isotopic variation have been established in mammalian hair. The relevance of these factors to collagen isotopic composition is unknown, but would be of great interest to zooarchaeological analyses of faunal skeletal tissue. METHODS The relationships between carbon (δ¹³C), nitrogen (δ¹⁵N), non-exchangeable hydrogen (δ²H) and oxygen (δ¹⁸O) values of defatted, demineralised and gelatinised bone collagen and defatted wool keratin from two sheep flocks (n = 20, 5) in the UK were investigated, including testing for the effects of nutritional plane, sex, pregnancy and season of sample collection. The sulfur composition (δ³⁴S values) was also investigated for tissues from the smaller flock. RESULTS Bulk collagen was enriched in ¹³C over bulk keratin by 2.0 - 2.7‰ and in ²H by 29 - 40‰ but depleted in ¹⁸O relative to keratin by 1.8‰. Differences in δ¹⁵N values were within experimental error. The collagen samples were generally more enriched in ³⁴S than keratin, but this was very variable. Pregnancy, sex and season, but not nutritional plane, significantly affected isotope values but did not change overall keratin-collagen relationships. CONCLUSIONS This dataset provides a baseline measure of variability and comparability for isotopic investigations into origin and husbandry conditions in archaeological sheep tissues, both collagen and keratin.