The ubiquitin-proteasome pathway influences many biological processes, including cell degradation and protein homeostasis maintenance. Many studies have shown that ubiquitin may be relevant to heat shock proteins [38, 39]. For instance, heat shock cognate 70 kDa proteins are synthesized in haploid cells during spermatogenesis and are mainly activated at the spermatid stage , which may help ubiquitin and target nonrepairable proteins to the proteasome . In the present study, a ubiquitin gene was found to be significantly upregulated in SP (Table 3). The serpin (serine proteinase inhibitor) family is reported to be exclusively expressed in the rat cauda epididymis and is upregulated, induced by androgens, and is secreted into the lumen to cover the sperm head. It can transform immotile spermatids into motile and fertilization-competent spermatozoa . Here, we identified two upregulated unigenes, CL4939.Contig2 and CL5743.Contig1, that were annotated as serine proteinase inhibitors.