Stable isotope analysis and variation in medieval domestic pig husbandry practices in northwest Europe: absence of evidence for a purely herbivorous diet

Stable isotope ratios have been widely used to infer past diets, domestication and husbandry practices of pigs, but few studies have addressed the proper baselines for such inferences. We analysed the diet of pig Sus scrofa from stable isotope analysis of carbon (delta C-13) and nitrogen (delta N-15) values of collagen from, urban Bergen, Norway (1300-1400AD). These were compared with values from Skipshelleren (5500BC-200AD); and from other medieval sites in NW Europe. Results indicated that the pigs from Bergen ate a very high proportion of marine protein compared to pigs and wild boar from Skipshelleren who ate a diet primarily of plant material. Results froth other medieval sites in NW Europe show considerable variation in delta C-13 and delta N-15 values, indicating large variations in diet. However, none of the values are consistent with a diet wholly dominated by plant material; and therefore pig husbandry through outspan herding (pannage) without supplementary feeding. We question interpretations to the contrary, which neglect the role of known differences in dietary fractionation between species in producing delta C-13 and delta N-15 values of tissue. Data from domestic pigs of ancient breeds undoubtedly raised by outspan herding/pannage are so far unavailable and would be instructive. (C) 2014 Elsevier Ltd. All rights reserved.