Spermatogonial stem cells (SSCs) from livestock species have the potential to be used for reproductive technologies and for the production of transgenic animals. The isolation of a relatively pure population of SSCs from livestock species has proven difficult; however, the recent advances in the production of induced pluripotent stem (iPS) cells may provide an alternative source of SSCs through the differentiation of iPS cells toward the germline. The general aim of this thesis was to produce bovine iPS cells that may be differentiated toward the germ line for potential use in reproductive technologies such as germ cell transplantation. Due to difficulties in isolating a pure population of bovine SSCs, methods to improve the enrichment of these cells are of interest in order to improve the success of bovine germ cell transplantation. A number of different methods to enrich bovine spermatogonia were trialled to determine which of the method for enrichment was most effective. The combination of enrichment by differential plating followed by separation of cells by discontinuous Percoll gradient centrifugation, was found to isolate the most enriched population of un-differentiated spermatogonia.

Germ cell transplantation has been shown to be a useful technique for studying spermatogenesis in rodents. In livestock species, the germ cell transplant technique could be used to produce transgenic animals and as a reproductive technology in extensive production systems. One of the contributing factors to poor success thus far has been poor recipient preparation, such as depletion of endogenous germ cells. This thesis investigated four depletion methods known to affect germ cells; heat, cold, chemotherapy (Busulfan) and irradiation. ... This thesis has found that testicular irradiation is the most successful method tested to deplete endogenous spermatogonia in the sheep testis. In addition, irradiated testes can support both endogenous and donor derived spermatogenesis. It seems that irradiation at high doses (15Gy) at the peri-pubertal to pubertal stage of testicular development can produce suitable recipients for germ cell transplantation and therefore is a potential methodology to increase the efficiency of germ cell transplants in livestock species.