Comparative Analysis of In Vitro Aging in Liquid-Preserved Boar and Bull Semen Stored at 5°C and 16°C

Although the prolonged liquid preservation of porcine and bovine semen is an attractive alternative to cryopreservation, the quality of the semen deteriorates over time due to in vitro aging.

To investigate the in vitro aging of porcine and bovine sperm after prolonged liquid preservation at 5°C and 16°C.

Semen was collected from 10 Piétrain boars and 10 Holstein Friesian bulls. After dilution (boar: Androstar Premium; bull: Caprogen), semen samples (boar: 20 × 10⁶/mL; bull: 40 × 10⁶/mL sperm) were divided into two portions, which were stored at 5°C and 16°C for 6 days. Basic sperm quality parameters, such as progressive motility, thermo-resistance after 30 (TRT30) and 120 (TRT120) min at 38°C, and sperm morphology, as well as advanced multicolor assays, were examined on Days 1, 3, and 6 to evaluate viability, acrosome integrity, plasma membrane fluidity, intracellular calcium levels, and mitochondrial membrane potential. The data analysis was done using a general linear model (GLM) with repeated measures.

Compared to 5°C, boar semen showed significantly higher values for TRT120, viable and acrosome-intact sperm with low membrane fluidity and intracellular calcium (VAI-LMLC), and VAI with high mitochondrial membrane potential (VAI-HMMP) at 16°C. Bull semen demonstrated superior quality when stored at 5°C. The GLM revealed significantly higher values for TRT30, TRT120, morphology and VAI on Day 3 at 5°C compared to 16°C. Over the course of all storage days, the mean values of VAI-LMLC and VAI-HMMP were significantly higher at 5°C.

Although basic semen quality could be maintained for 6 days in liquid-preserved boar and bull semen, advanced semen quality parameters revealed differences in the in vitro aging of boar and bull sperm that were specific to species and storage temperature.