Winter pasturing practices and variable fodder provisioning detected in nitrogen (δ15N) and carbon (δ13C) isotopes in sheep dentinal collagen

Abstract

Identifying the isotopic signatures in animal bones and teeth associated with husbandry practices has important implications for understanding the subsistence strategies in use by prehistoric and modern herders alike. While the nitrogen isotopic composition of ungulate collagen derived from teeth is now commonly used to examine shifts in the age at which young animals are weaned, the utility of nitrogen isotopes to identify other important husbandry practices has yet to be fully explored. Here, the δ15N composition of tooth dentin collagens from modern, traditionally managed caprines from Mongolia are measured alongside graze plants obtained from both summer and winter pasture grounds. Nitrogen isotopic curves obtained from sequentially sampled second molars, which form primarily during the winter months, indicate a steady increase in δ15N values proceeding from the top to the bottom of the tooth. Ingestion of graze from winter pastures, which exhibit significantly higher δ15N values compared to summer pasture graze due to the regular addition of dung by herd animals to winter pasturages, likely accounts for this pattern. These data suggest that nitrogen isotopic analyses are useful not only for identifying animal management practices such as weaning, but also for identifying practices concerned with manipulation of the plant-based portion of the animal diet. In addition, variation in carbon isotopic curves from second molars suggests that differences in the intensity of fodder application can be observed in individual animals.