PSV-5 - Relationship Between Sire Conception Rate, Sperm Motility, Sperm SERPINA5 Relative Concentration, and in vitro Produced Embryos in Dairy Bulls

Sire conception rate (SCR) is a field measure of fertility among bulls, but it can be influenced by several factors (Sperm transport, sperm-egg binding, early embryo development, etc). The objective of this study was to evaluate the relationship between SCR, sperm motility, SERPINA5 concentrations, and in vitro embryo development. Measurements were performed in 19 bulls with SCR values ranging from -7.7 to 4.45. For each bull, an aliquot of frozen-thawed semen was used for analyses of total (TMOT) and progressive (PROG) motility. Remaining semen was fixed with 2% formaldehyde, and concentration of SERPINA5 was determined by immunolocalization (antibody SERPINA5/Dylight405; PA5-79976-Invitrogen / ab201798-Abcam). Mean fluorescence intensity was determined in ~200 sperm heads/bull. Approximately 149 oocytes/bull were fertilized in vitro for embryo development analysis (cleavage and blastocyst rates). Statistical procedures were performed in SAS (9.4) using the procedures CORR for correlations (SCR, TMOT, PROG, SERPINA5, cleavage and blastocyst) and GLIMMIX for comparison of “field-fertility” (SCR divided in HIGH or LOW) and “field-embryo-fertility” (LOW-SCR sires were divided based on blastocyst rate (HIGH or LOW) resulting in two classifications; LOW-HIGH≥31% and LOW-LOW≤26%, respectively). There were positive correlations (P < 0.05) between cleavage-blastocyst (r=0.50), SERPINA5-cleavage (r=0.48), and TMOT-PROG (r=0.76). Sire SCR was not associated with SERPINA5, TMOT, PROG, cleavage and blastocyst rate (P > 0.52). Among LOW-SCR sires, LOW-LOW sires (-4.83±0.60) tended to have a better SCR score than LOW-HIGH (-6.18±0.42) sires (P = 0.08), but there were no differences (P > 0.43) between LOW-HIGH, LOW-LOW, and HIGH sires for SERPINA5, TMOT, PROG, and cleavage. In conclusion, some LOW SCR sires have good embryo development indicating a different mechanism for their low SCR; however, these differences in SCR could not be explained by TMOT, PROG, SERPINA5, cleavage and blastocyst. There were, however, positive correlations between cleavage-blastocyst rate, and SERPINA5-cleavage rate.