What question did this study set out to answer?

To evaluate the effects of oral melatonin supplementation on semen quality and testicular temperature in bulls.

April 4, 2026

Role of Oral Melatonin in Improving Semen Quality and Thermal Regulation of the Testes in Bulls

Key Points

To evaluate the effects of oral melatonin supplementation on semen quality and testicular temperature in bulls.
Yearling Angus bulls were divided into melatonin (MEL) and control (CON) groups.
MEL bulls received daily melatonin supplementation, while CON received an ethanol control.
Semen samples were collected on specific days for analysis of motility and flow cytometry.
Scrotal temperatures were monitored using thermal imaging at multiple time points.
Data were analyzed using SAS's MIXED procedure.
MEL bulls showed greater sperm motility on D28 compared to CON.
On D56, MEL exhibited significantly higher progressive motility and other kinematic measures.
MEL had a lesser relative increase in LIN post-thaw compared to CON.
Flow cytometry showed higher intracellular calcium in MEL on D28.
No significant differences in scrotal temperatures were observed between groups.

Abstract

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.

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