Abstract This study examined the impact of oral melatonin supplementation on fresh and post-thawed sperm traits as well as scrotal temperatures. Yearling Angus bulls (n = 21) were randomly allocated into two groups, melatonin (MEL; n = 11) or control (CON; n = 10) diets from October 2024 to January 2025. MEL bulls were supplemented with 200 μg/kg of body weight of melatonin dissolved in ethanol (5.31 ± 0.05 mL), while CON bulls were supplemented with an equivalent ethanol vehicle control (5.21 ± 0.05 mL) daily via the CALAN gate feeding system. Semen, obtained via electroejaculation were collected on D 0, 28, and 56. Subsequently, a 1 mL aliquot of raw semen was removed for extension and cryopreservation. Kinematic parameters were analyzed in fresh and post-thawed semen via computer-assisted sperm analysis (CASA). Further, cryopreserved semen, from each collection, was also used for flow cytometry. Additionally, scrotal temperatures were collected via FLIR E75 thermal camera on D 0, 14, 28, 42, 56, 70, and 87. Sperm and scrotal temperature data were analyzed using the MIXED procedure of SAS. MEL had greater (P = 0.01) sperm motility on D28 compared with CON (83.7 ± 3.3 vs 72.0 ± 3.1). Additionally, on D56 MEL had greater progressive motility (P = 0.02; 38.2 ± 4.6 vs 24.7 ± 2.5), LIN (P = 0.02; 42.4 ± 1.9 vs 35.7 ± 1.4), and STR (P = 0.01; 76.7 ± 1.8 vs 68.9 ± 1.6) compared with CON. Interestingly, MEL had lesser ALH (P = 0.01; 8.4 ± 0.2 vs 9.3 ± 2.3), VAP (P = 0.005; 103.0 ± 2.6 vs 115.6 ± 2.5), VCL (P = 0.008; 193.6 ± 6.1 vs 220.5 ± 5.7), and VSL (P = 0.03; 77.8 ± 2.2 vs 85.5 ± 2.1) on D0 compared with CON, however by D28 there were no differences between the groups (P 0.1). When the change in sperm parameters, expressed as a relative difference, were compared between fresh and post-thaw semen MEL had a lesser relative increase in LIN (P = 0.007; 2.0 ± 2.0 vs 11.2 ± 1.7) compared with CON on D56. For flow cytometric analysis, MEL had greater intracellular calcium staining intensity (P = 0.02; 20595 ± 1174.9 vs 16486 ± 1036.2) on D28, indicating an increased concentration of intracellular calcium. Lastly, there were no differences in scrotal temperatures between groups during the treatment period (P 0.1). Melatonin supplementation from fall to winter had both acute and long-term impacts on sperm kinematic and flow cytometric parameters. Factors related to motility were improved without negatively affecting scrotal temperatures.
Mills et al. (Wed,) studied this question.