Upregulation of CRISP‐3 and kallikrein in stallion seminal plasma is associated with poor tolerance of cooled storage

For unknown reasons, stallion fertility and sperm longevity during cooled storage of semen vary markedly between individuals. Spermatozoa from individual stallions react differently to the presence, or the removal, of seminal plasma (SP). The aim was to evaluate differences in protein content in stallion seminal plasma with either a positive or a negative effect on sperm chromatin integrity during storage. Stallion semen samples from different ejaculate fractions were stored at 5°C for 24 hr. Sperm survival was assessed after storage using a sperm chromatin structure assay. Protein expression in SP with either positive or negative effects on sperm survival during storage was studied using two‐dimensional differential gel electrophoresis and liquid chromatography–mass spectrometry. Lower sperm chromatin integrity was associated with upregulation of the proteins kallikrein, CRISP‐3 and HSP‐1, while higher chromatin integrity was associated with upregulation of TIMP‐2. In the sperm‐rich fractions, kallikrein and CRISP‐3 differed significantly between SP samples with differing effects on sperm chromatin integrity. In the sperm‐poor fractions, TIMP‐2 and HSP‐1 differed significantly between the two SP groups. Differences in the seminal plasma proteome are associated with sperm longevity during cooled storage.