Bull field fertility differences can be estimated with in vitro capacitation and flow cytometry

Authors: ZOCA, SAULO - South Dakota State University; Geary, Thomas; Zezeski, Abby; KERNS, KARL - Iowa State University; DALTON, JOSEPH - University Of Idaho; HARSTINE, BO - Select Sires, Inc; UTT, MATTHEW - Select Sires, Inc; Cushman, Robert - Bob; WALKER, JULIE - South Dakota State University; PERRY, GEORGE - Texas A&M University

Submitted to: Society for the Study of Reproduction Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 10/1/2021
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Sperm must undergo capacitation before being capable of fertilizing an oocyte. Capacitation is a biochemical cascade of events that occur in the female reproductive tract. Once capacitation occurs, the lifespan and fertilization capacity of bovine sperm has been estimated to be approximately 30 h. Sperm capacitation can also be induced in vitro by glycosaminoglycans (i.e. heparin). This study was conducted to evaluate whether post in vitro capacitation changes in sperm could be used to estimate fertility differences between bulls. Frozen-thawed semen from five bulls (two to four ejaculates per bull) previously identified with high (48.1% and 47.7%, bulls A and B, respectively), intermediary (45.5%, bull D) or low (40.7% and 43.1%, bulls C and E, respectively) conception rates, based on two field trials, was diluted with capacitation media (CM) to 17 million sperm/mL. Sperm were evaluated for total and progressive motility using a computer assisted sperm analysis (CASA) system. Flow cytometry (10,000 sperm/sample) was used to evaluate sperm plasma membrane integrity (viability), acrosome integrity (viable sperm with an intact or disrupted acrosome), reactive oxygen species (ROS; viable sperm ROS+ or ROS-), mitochondrial membrane energy potential (mito-potential), and zinc signatures (signatures 1 to 4) at pre-wash (CASA only), post-wash (CASA only), h 0 (diluted with non-capacitation media), and at h 0, 3, 6, and 24 after dilution with CM and incubation at 37ºC. Data were analyzed using the GLIMMIX procedure of SAS with bull, time and the interaction as fixed effects. A random statement was used to analyze the data as repeated measures by time with ejaculate per bull as subject. Residual and intercept were also considered random. Bull by time interaction was significant (P=0.03) for total motility, viable sperm with disrupted acrosome, and zinc signature 3. There tended (P=0.06) to be a bull by time interaction for zinc signatures 1+2. Time was significant (P=0.003) in all analyses, except viable ROS- (P=0.12). There was a significant effect of bull (P=0.03) for viable sperm, viable sperm with disrupted acrosome, zinc signatures 1, 2 and 1+2. High and intermediary field fertility bulls had greater (P=0.04) percentages of viable sperm (23.2±1.9%, 26.8±2.9%, 24.2±2.2%, 16.9±2.3%, 13.6±1.6%, A, B, D, C and E, respectively), zinc signature 2 (18.3±1.7%, 17.4±2.4%, 18.9±2.0%, 9.9±1.9%, 10.5±1.4%, A, B, D, C and E, respectively) and zinc signature 1+2 (21.4±1.8%, 23.1±2.6%, 22.7±2.2%, 4.8±2.2%, 11.5±1.4%, A, B, D, C and E, respectively) compared to low field fertility bulls. Viable sperm with an intact acrosome also tended to differ (P=0.06) amongst bulls; however, association with field fertility was not observed. There was a positive correlation between conception rates and viability (P=0.10; r=0.81), zinc signature 2 (P=0.04; r=0.89), and zinc signature 1+2 (P=0.10; r=0.80). In summary, incubation of sperm in CM and flow cytometry analysis for viability and zinc signatures seems promising to estimate in vivo fertility differences amongst bulls.