Influence of season and plasma prolactin concentrations on fertility of Bos taurus beef bulls

Research output: Other contribution to conferenceAbstractpeer-review


Prolactin is known to influence testicular function in beef bulls, but the relationship between plasma prolactin concentrations and semen quality parameters (e.g. sperm motility and morphology) is unclear. Furthermore, both seasonal variability and innate circadian rhythms can potentially influence plasma prolactin concentrations, complicating efforts to characterize the relationship between prolactin and bull semen quality parameters. Objective was to assess seasonal variability in bull plasma prolactin concentrations and determine its relationship with semen quality parameters. Twelve mixed-age beef bulls (7 Angus and 5 Limousin) were used. Bulls were yarded, had blood collected, and examined for breeding soundness on the last week (± 1 week) of each month from April to December. Reproductive parameters assessed included scrotal circumference (SC), progressive motility (PM) of sperm (assessed using computer assisted sperm analysis), and sperm morphology. Plasma prolactin concentrations were quantified using a commercial bovine prolactin ELISA kit (bPRL, AssayGenie). Results indicated that plasma prolactin concentrations were lower (p = 0.043) in summer compared to winter in contrast to previous findings. Plasma prolactin concentrations and daylength (measured in hours) were negatively correlated (r = -0.23, p = 0.040), but the correlations between plasma prolactin concentrations and reproductive parameters were not significant (prolactin versus SC: r = -0.041, p = 0.736; prolactin versus sperm morphology: r = -0.03, p = 0.789; prolactin versus PM: r = 0.02, p = 0.923). Bull age had influence on both percentage normal sperm (p = 0.032) and SC measurements (p = 0.025). Older bulls tended to have larger SC and more morphological sperm abnormalities. Month of sampling significantly influenced SC. Overall, plasma prolactin concentrations had influence on seasonal variability, and although no relationship was identified between plasma prolactin concentrations and male reproductive parameters, this could likely be attributed to the relatively small sample size, insufficient statistical power, and infrequent sampling. Future studies investigating this relationship in larger populations, accounting also for seasonal variability, are warranted. Keywords: Bull, beef cattle, fertility, prolactin, season
Original languageEnglish
Number of pages1
Publication statusPublished - 19 Jul 2023
EventSociety for Theriogenology Conference 2023: Therio Conference - Sheraton Birmingham Hotel , Birmingham, United States
Duration: 19 Jul 202322 Jul 2023 (Proceedings)


ConferenceSociety for Theriogenology Conference 2023
Country/TerritoryUnited States
Internet address


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