Sperm characteristics of maternal composite rams before and after the breeding season

Authors: Snider, Alexandria - Alex; Freking, Bradley - Brad; Miles, Jeremy; Rempel, Lea; Crouse, Matthew; Cushman, Robert - Bob; WILDEUS, STEPHAN - Virginia State University; Murphy, Thomas - Tom

Submitted to: Society for the Study of Reproduction Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 4/29/2022
Publication Date: 7/18/2022
Citation: Snider, A.P., Freking, B.A., Miles, J.R., Rempel, L.A., Crouse, M.S., Cushman, R.A., Wildeus, S., Murphy Jr, T.W. 2022. Sperm characteristics of maternal composite rams before and after the breeding season [abstract]. Society for the Study of Reproduction Annual Meeting, July 26-29, 2022, Spokane, Washington. Poster P233.

Interpretive Summary:

Technical Abstract: In the livestock industry, ruminant males are submitted for breeding soundness evaluations (BSE) prior to the breeding season and can be tested again after the breeding season. Post-breeding BSEs can be performed to determine negative impacts of the environment or poor fertility following the breeding season. Yearling males are commonly used in a breeding program, and it is not well known how their fertility maintains over a breeding season. Preliminary data from our lab demonstrated the impacts of a 28-d breeding season on yearling bull performance compared to bulls that were not utilized for breeding. Yearling bulls utilized for breeding had a reduction in sperm concentration per mL and reduced spermatic kinetics after breeding compared to bulls not utilized for breeding. This led us to investigate if breeding season and age impacts other ruminant males (i.e., sheep) for sperm production and kinetic evaluation. The objectives were to evaluate differences in ram sperm cell parameters before and after a 21-d breeding season. Semen was collected by electroejaculation from the same group of Composite-IV rams before (n=24) and after (n=21) the breeding season, (a 50-d interval), and analyzed by a computer-assisted sperm analysis (CASA) system. Traits were modeled as repeated measures with fixed effects of age class (young: 2.6 ± 0.01 yr vs. mature: 4.2 ± 0.8 yr), collection timepoint (pre- vs. post-breeding), and their interaction with ram as a random effect. The age class x collection timepoint interaction was only significant for progressive motility (P=0.05) due to a decrease from pre- to post-breeding within young rams (47 vs. 34%; P = 0.04) that was not observed in mature rams (P=0.42). The main effect of age class did not influence any sperm cell parameter evaluated (P=0.23). Presence of proximal droplets (2.2 vs. 77%), bent tails (2.1 vs. 7.7%), and coiled tails (0.4 vs. 2.3%) increased from pre- to post-breeding (P<0.001). Within motile sperm, mean head area increased from pre- to post-breeding (15 vs. 37 µm2) and reduced sperm head elongated (0.46 vs. 0.34; P < 0.001). A reduction was also observed for sperm motion and velocity traits: distance on an average path (DAP; 84 vs. 65 µm), velocity on an average path (VAP; 191 vs. 161 µm/s), and straightness (89 vs. 83%) from pre- to post- breeding analysis (P<0.001). Progressive motility is decreased in young rams after the breeding season, while mature rams remained constant. This can be attributed to reduced maturity and potential inability to perform during a 35-d breeding season. Sperm kinetic parameters DAP and VAP were reduced in rams after the breeding season independent of age. These results could be due to constant production of sperm without the time required for complete maturation during the breeding season, indicated by increased presence of proximal droplets. Future evaluations will consider the relationship of sperm cell characteristics over time with siring capacity of rams in competitive mating environments. USDA is an equal opportunity provider and employer.