Annual dynamics of semen-dose production in boars for commercial artificial insemination

Introduction. Semen-dose production in boar artificial insemination centers depends on the temporal stability of ejaculate quality, yet calendar-associated fluctuations remain insufficiently described under tropical commercial conditions. Objective. To characterize the monthly dynamics of semen-dose yield per ejaculate in boars managed under tropical commercial artificial insemination (AI) conditions and identify the annual periods associated with reduced ejaculate productivity. Materials and methods. The study was conducted on commercial pig farms in northwestern Costa Rica between 2020 and 2024. A total of 461 ejaculates from 119 sexually mature boars were evaluated. Each ejaculate was macroscopically assessed to determine and quantify the number of semen doses that could be prepared. A dose from each ejaculate was transported to the laboratory at 17 °C. Total and progressive motility were evaluated using ISAS® v1, and sperm morphology was assessed after sample fixation with the Trumorph® system. Only ejaculates containing ≥75 % morphologically normal spermatozoa were analyzed. Monthly patterns were analyzed using mixed-effects models that included month, farm, year, and age at collection as fixed effects and boar as a random effect. Results. Sperm concentration, total and progressive motility, and semen-dose yield varied markedly throughout the year. Concentration increased early in the year, peaked in March, declined toward June, and remained low until October before recovering. Total and progressive motility showed a distinct monthly pattern, with lower values during the first half of the year and improved performance thereafter. Semen-dose yield showed a prolonged low-output period from February through July, followed by recovery from August onward. Conclusions. Ejaculate productivity in tropical boars followed a marked annual pattern. Identifying the low-output period may allow AI centers to anticipate adjustments in collection schedules, boar allocation, and semen-dose availability.