Yearling bulls have reduced sperm concentration and increased seminal plasma interleukin-8 after a 28-day breeding season

Authors: Snider, Alexandria - Alex; MCCARTHY, KACIE - University Of Nebraska; Wright, Elane; Ondrak, Jeff; Oliver, William; DAHLEN, CARL - North Dakota State University; Cushman, Robert - Bob; Crouse, Matthew

Submitted to: Reproduction in Domestic Animals
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2022
Publication Date: 8/4/2022
Citation: Snider, A.P., McCarthy, K.L., Wright-Johnson, E.C., Ondrak, J.D., Oliver, W.T., Dahlen, C.R., Cushman, R.A., Crouse, M.S. 2022. Yearling bulls have reduced sperm concentration and increased seminal plasma interleukin-8 after a 28-day breeding season. Reproduction of Domestic Animals. 57:1465-1473. https://doi.org/10.1111/rda.14223.
DOI: https://doi.org/10.1111/rda.14223

Interpretive Summary: Breeding soundness examinations are important for evaluating bulls prior to the breeding season, but bulls are not commonly examined after a breeding season. Yearling bulls are commonly used in multi-sire pastures and assumed to maintain fertility throughout the breeding season. Limited research has investigated how breeding activity impacts breeding soundness over time. The current study examined the impact of a 28-day breeding season on yearling bulls spermatogenic parameters of quality, metabolic, and cytokine profiles. Yearling bulls exposed to females had reduction in sperm concentration/mL and inflammatory cytokines in their seminal plasma. This information provides insight on how fertility of yearling bulls changes throughout the breeding season, thus allowing producers to make decisions on how to manage their bulls to optimize reproductive efficiency in the herd.

Technical Abstract: We hypothesized that yearling bulls selected for a 28-d breeding season would have reduced sperm concentrations and morphology, and have increased seminal plasma concentrations of pro-inflammatory cytokine interleukin-8(IL-8). Yearling bulls were selected based on a breeding soundness examination (BSE) at approximately 415 d of age and contained at least 750 million sperm in the ejaculate, with 12 bulls randomly selected for breeding (BREEDERS) and 12 bulls not selected for breeding (NON-BREEDERS). After a 28-d breeding period, all bulls underwent a BSE. Plasma and seminal plasma were collected at each time point for analysis. Data were analysed utilizing either the MIXED or GLIMMIX procedures with repeated measures in SAS with breeding group, age and the interaction as fixed effects. Sperm concentration per ml of ejaculate was reduced (p < .05) in yearling bulls used for breeding compared with those not used for breeding at the end of the breeding season. Seminal plasma IL-8 concentrations in yearling bulls used for breeding were increased (p < .05) after the breeding season compared with bulls not used for breeding. Taken together, yearling bulls selected for a 28-d breeding season have reduced sperm production per ml of an ejaculate and increased inflammatory response in the seminal plasma that can lead to impaired breeding response if they are to be used for more than 30 d of breeding.