Proteomic analysis of cryoconserved bull sperm to enhance ERCR classification scores of fertility

Breeding of dairy cattle for high production and the reproductive management of herd is the biggest problem and it accounts for a large part on costs of production. A negative association has been observed between the level of livestock production and fertility. This is linked both to genetic factors (inbreeding and high production) and physiological factors (metabolic by high production)1. A lot of resources have been used for enhancement of cattle fertility but few studies and interventions are reported to control and to enhance the effect on the bull reproductive efficiency. As the patterns of selection and reproductive management of dairy cattle is based on the use of artificial insemination (AI) it is easy to understand the importance of assessing the level of fertility of bull breeder. One method of evaluating relative sire fertility currently used is the estimated relative conception rate (ERCR). ERCR is the difference in conception rate (nonreturn rate at 56 day) of a sire compared with other AI sires used in the same herd2. In this work the nonreturn rate was estimated at 56 d for first insemination of lactating cows (www.anafi.it). At present, validation of genomic markers that are able to predict with high confidence high or low fertility of a given sire it is very difficult using population estimates of sire fertility. The reason is because these methods do not measure the bull ‘true fertility’3. To unravel the biological display of the bull genome, proteomics, that focus at the protein level could lead to the development of novel biomarkers that may allow for detection of bull fertility levels4,5. The aim of this study is to evaluate, through the differential proteome analysis, changes in protein expression profiles of spermatozoa from bulls with high fertility (high ERCR score) and low fertility (low ERCR score) in order to identify possible protein markers to be used as indices of fertility.