Inferring Castration Status and Age-at-Death from Sheepskin Parchments

Secondary products such as traction from cattle, wool from sheep, and mobility from horses are invaluable outputs from rearing livestock. The innovative herd management practice of castration enables non-breeding males to be managed safely beyond typical ages of slaughter, greatly improving the productivity of livestock herds. Although osteological methods can identify some morphological differences between castrated and intact males, it is difficult to make clear distinctions between them. However, methylation values are affected by the considerable hormonal changes that occur as a result of castration. For example, castrated male sheep have shown lower biological ages compared to age-matched intact rams (Sugrue et al., 2021). Furthermore, age-at-death has been predicted from reconstructed methylation values in ancient horses, informing on culling practices (Liu et al., 2023). Using an aDNA-specific bisulfite sequencing approach, we have reconstructed CpG methylation values from sheepskin parchments. We have developed machine learning models trained on modern sheep in order to infer traits of interest such as castration and age-at-death. The informative CpG sites have been incorporated into a target capture set to enable cost-effective sequencing of additional samples. This will enable the characterisation of these traits in ancient sheep across time periods, geographical locations, and archaeological contexts.