Three-dimensional growth of bovine hoof as recorded by carbon stable isotope ratios

To investigate the usefulness of bovine hooves as incremental tissues, the objective of this research was to gain a better understanding of hoof growth in three dimensions. In a controlled experiment, cattle were switched from a barley-based diet to a maize-based diet (C isotopic spacing between diets was 13.6 per thousand) and maintained on this experimental diet for 168 days. To compare growth rates along the hoof wall, three slices were sampled post-mortem from one bovine claw. In addition, one claw from each of three different animals was sampled at different depths from the surface to determine any possible time lag ('offset') in the laying down of keratin tissue layers. From each hoof as many as 41 superficial samples were taken over the first 60 mm, starting at the periople, and up to 12 samples were taken sequentially at increasing depths to a depth of 6 mm at five particular points on the surface. The growth rate of the abaxial wall of the bovine claw increased from the anterior to the posterior region of the bovine hoof. Analysis of the deep samples revealed that the deeper layers were younger than the surface layers. This offset was inversely related to the hoof growth rate, i.e. hooves with a high hoof growth rate showed a smaller offset. Observed offsets ranged between 9.2 +/- 1.8 days per mm in depth for a high and 14.0 +/- 2.8 days per mm in depth for a low hoof growth rate and were significantly different (t > or = 3.92, p < 0.0005, n = 19 or 27). The results of this study demonstrate that when sampling hooves or hoof fragments for applications such as diet reconstruction, careful consideration needs to be given to sample location.