Experimental determination of dietary carbon turnover in bovine hair and hoof

Stable isotopes measured in keratinized tissues like hair or hoof have proven to be a useful too] for reconstructing the dietary history of animals with a weekly to daily resolution. Quantitative reconstruction of dietary preferences requires a precise estimate of tissue turnover by means of controlled feeding experiments. We determined the turnover rates of carbon in hoof and tail hair of growing steers (Bos taurus L., 1758) fed a C(3)-based diet, followed by a C(4)-based diet, for 168 d. As with horses, turnover in steer hair was successfully described by a three-pool modelling approach, with apparent half-lives of 1.7, 7.7, and 69.1 d for each of the pools, each contributing 53%, 20%, and 28% of the total signal, respectively. Two pools only were identified in bovine hoof, which recorded the diet switch more slowly than hair with a reduction in the amplitude of short-term isotope changes. We interpreted this result as a sampling artefact and found that the hooves reflected the same pools as the hair if growth geometry is taken into account. The model parameters defined in this study allowed us to quantitatively reconstruct previous diets of steers of different breeds and individual history with a precision of +/- 1 parts per thousand.