Vet World   Vol.18   November-2025  Article - 17 

Sperm freezability is associated with melatonin receptor expression in the sperm plasma membrane of Saanen goat bucks (Capra hircus)

Background and Aim: Cryopreservation is an essential assisted reproductive technology for preserving valuable animal genetics; however, it induces osmotic and oxidative stress that compromises sperm quality. Melatonin (MLT) functions as both an antioxidant and a signaling molecule through specific membrane receptors, melatonin 1 (MT1) and melatonin 2 (MT2). This study aimed to determine the association between sperm freezability, MLT receptor expression on spermatozoa, and MLT concentration in the seminal plasma of goat bucks.

Materials and Methods: Semen samples were collected weekly from seven clinically healthy Saanen bucks (2–3 years) maintained under natural photoperiod and standardized feeding conditions. A total of 124 ejaculates were analyzed seasonally (spring-winter). Sperm quality parameters, including motility, viability, capacitation status (chlortetracycline [CTC] assay), plasma membrane fluidity, and acrosome integrity, were evaluated before and after cryopreservation. Expression levels of MT1 and MT2 receptors were quantified by Western blot, while MLT concentration in seminal plasma was measured by enzyme-linked immunosorbent assay. Pearson’s correlation and determination coefficients (R, R2) were computed to assess associations between sperm quality, receptor expression, and MLT concentration.

Results: Western blot analysis revealed variable MT1 (16 kDa) and MT2 (28–75 kDa) expression throughout the year. High negative correlations (R > −0.9, R2 > 0.8) were observed between the expression of both receptors and the proportion of acrosome-reacted (AR) spermatozoa (CTC-AR pattern), except for MT2 (75 kDa). Conversely, seminal plasma MLT concentration showed a strong positive correlation (R > 0.9, R2 > 0.8) with capacitated sperm having intact acrosomes (CTC-B pattern). Seasonal variation in receptor expression, rather than MLT concentration, influenced sperm cryoresistance.

Conclusion: Sperm freezability in goats is closely linked to the expression of MLT receptors and seminal plasma MLT concentration. Higher receptor expression corresponds to improved post-thaw sperm quality, likely by mitigating cryocapacitation and acrosomal damage. These findings suggest that enhancing MLT receptor expression or modulating photoperiodic exposure could optimize semen cryopreservation protocols and reproductive efficiency in caprine species.

Keywords: cryopreservation, freezability, goats, melatonin receptors, seminal plasma, spermatozoa.

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How to cite this article: Cardenas-Padilla AJ, and Medrano A (2025) Sperm freezability is associated with melatonin receptor expression in the sperm plasma membrane of Saanen goat bucks (Capra hircus), Veterinary World, 18(11): 3520-3535.

Received: 05-08-2025   Accepted: 22-10-2025   Published online: 27-11-2025

Corresponding author: Alberto J. Cardenas-Padilla    E-mail: acardenasp@cuautitlan.unam.mx

DOI: 10.14202/vetworld.2025.3520-3535

Copyright: Cardenas-Padilla and Medrano, et al. This article is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http:// creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.