Short-term diet changes revealed using stable carbon isotopes in horse tail-hair

1. We demonstrate the potential of extracting high-resolution dietary information from stable carbon isotopes ( δ 13 C) in horse tail-hair, in response to short-term changes in diet in controlled feeding experiments. 2. Tail hairs were sampled from six horses that had been equilibrated to C3 forage and were then subjected to a series of short-term diet switches to the C4 Coastal Bermuda Grass ( Cynodon dactylon L.). Four of these horses were equilibrated to Alfalfa ( Medicago sativa L.) and were then subjected to 1-, 3and 7-day diet spikes of the C4 grass. The remaining two horses were equilibrated to a C3 grass mix ( Dactylis glomerata L. and Festuca arundinacea Schreb.) and then subjected to a 7-day diet spike of C4 grass. 3. The effects of the short-term diet switches were easily observable in the hair. The 1-, 3and 7-day spikes showed an increasing deviation from the prespike equilibrium value of 1·0‰, 2·9‰ and 5·6‰ (7-day treatments averaged). 4. Isotopic chronologies of individual hairs were created and plotted against a threepool, exponential-decay model. With small alterations to the original model parameters, our data are well explained by this model. 5. This study indicates that information about diet is recorded with high resolution in hair. This method could be applied to both modern and ancient samples, greatly enhancing the temporal resolution of diet reconstruction studies.