Unravelling the bull fertility proteome

In the last few decades a negative association between the level of milk production and fertility has been observed. Currently, the most utilized method of measuring male fertility employed by the livestock industry is related to the Non-Return Rate (NRR). Through differential proteome analysis, this study evaluated changes in the expression of the protein profile of spermatozoa collected from 16 bulls with different levels of field fertility expressed as an estimated relative conception rate (ERCR). The main aim is to identify putative protein markers to be used as putative indices of fertility. Two dimensional electrophoresis coupled with mass spectrometry analysis was used for protein separation and identification. To improve differential proteome analysis among experimental groups, a part of shotgun MS analysis was also performed. Three protein spots showed a differential expression pattern among all ERCR classes. Alpha enolase was significantly down-regulated in the ERCR- group, while two other proteins, isocitrate dehydrogenase and triosephosphate isomerase, were up-regulated in ERCR- in comparison to ERCR+. Alpha-enolase and isocitrate dehydrogenase subunit alpha (IDH-alpha) have been described in the literature for having a potential role in bull fertility. The possibility of determining protein biomarkers for fertility is more useful and less expensive than ERCR for acquiring rapid estimation of fertility because it does not require the use of field insemination trials. Shotgun MS analysis conducted on the same samples revealed 7 proteins down-regulated in the ERCR- group and 1 protein up-regulated. Among these proteins, calmodulin, ATP synthase mitochondrial subunits alpha and delta, malate dehydrogenase and sperm equatorial segment protein 1 were shown to be linked with sperm fertility.