_1780292298 20260601053818000 Rovedar Daryoushbabazadeh@gmail.com Rovedar Journal of Veterinary Physiology and Pathology J. Vet. Physiol. Pathol. 2821-0328 12 09 2025 4 4 Innocent Jonah Gosomji https://orcid.org/0000-0002-8727-3217 Oludayo Akinsola https://orcid.org/0000-0003-3981-5672 Abdullahi Baso https://orcid.org/0000-0001-6731-853X Nura Ahmed https://orcid.org/0009-0002-0137-3987 Jamiu Oyewole Omirinde https://orcid.org/0000-0002-2952-9376 Idris Ayodeji Azeez https://orcid.org/0000-0001-5858-1395 Naanman James Plang https://orcid.org/0000-0001-5695-6325 Nenchini Bala Koplamma Sunday Akau Hena https://orcid.org/0000-0002-5231-4947 Introduction: Guinea fowls have sophisticated seasonal mechanisms that make them an excellent model for studying reproductive activities. The present study aimed to investigate the impact of exogenous melatonin and artificial light on testicular morphometry in sexually mature guinea fowls.Materials and methods: A total of 65 mature male guinea fowls, with an average weight of 1-2 kg, were randomly selected for the present study. Five guinea fowls were utilized for the primary evaluation study on day 0. Sixty guinea fowls were divided into six groups with 10 guinea fowls in each group. The first group (SD) was exposed to 8 hours of light and 16 hours of darkness (8L:16D). The second group (SD-Mel) was exposed to 8L:16D with an additional melatonin injection. The third group was the control group (CTL) with 12L:12D. The fourth group was maintained on CTL with an additional injection of melatonin (CTL-Mel). The fifth group (LD) was exposed to 16L:8D, and the sixth group was exposed to 16L:8D with an injection of melatonin (LD-Mel).  Melatonin was administered intramuscularly at 1 mg/kg body weight 2 hours before the end of each light cycle. The entire study was conducted in 60 days. Body weight (BW), testicular weight, and gonado-somatic index (GSI) were recorded at days 0, 30, and 60 of the study.Results: There was a consistent increase in the BW, testicular weight, and GSI from days 0 to 60 in all groups. The results of BW, testis weight, and GSI were statistically significant on days 0, 30, and 60 across all groups. The testicular weight was higher in SD and LD-Mel, while the lowest weight was in SD-Mel. The GSI was higher in SD and LD-Mel, while the lowest was in SD-Mel. In the LD-Mel and LD groups, there was a strong positive correlation between testes and GSI.Conclusion: Melatonin exposure, particularly under long-day conditions, enabled guinea fowl to improve reproductive potential by day 30 of light treatment. 12 29 2025 64 68 https://creativecommons.org/licenses/by/4.0 10.58803/jvpp.v4i4.76 https://jvpp.rovedar.com/index.php/JVPP/article/view/76 https://jvpp.rovedar.com/index.php/JVPP/article/download/76/100 https://jvpp.rovedar.com/index.php/JVPP/article/download/76/100 Oke OE, Adejuyigbe AE, Idowu OP, Sogunle OM, Ladokun AO, Oso AO, et al. Effects of housing systems on reproductive and physiological response of guinea fowl (Numida meleagris). J Appl Anim Res. 2015; 88: 47-55. Available at: https://www.cabidigitallibrary.org/doi/full/10.5555/20153192625 Houndonougbo PV, Bindelle J, Chrysostome CAAM, Hammami H, and Gengler N. Characteristics of guinea fowl breeding in West Africa: A review. Tropicultura. 2017; 35(3): 222-230. Available at: https://popups.uliege.be/2295-8010/index.php?id=1283&file=1 10.1177/074873001129002079 10.3389/fnins.2014.00115 10.1016/j.jphotobiol.2017.09.005 10.1016/j.yhbeh.2004.11.008 10.1590/S0102-09352013000400003 10.1051/rnd:2005065 10.1186/1742-9994-8-1 10.1002/jez.1741 10.1016/j.ygcen.2014.09.003 10.54058/saheljvs.v19i3.320 10.1016/j.vas.2022.100282 10.1016/j.anireprosci.2024.107410 10.3389/fphys.2024.1501334 10.3389/fcell.2024.1338828 10.1095/biolreprod.108.075655 10.1016/j.theriogenology.2022.02.027 10.1111/and.14597 10.3390/su14031160 10.3923/ijps.2008.1204.1206 Flecknell PA. Laboratory Animal Anesthesia. 3rd edition. London, U.K.: Academic Press; 2009. p. 25-237. Available at: https://www.fcq.unc.edu.ar/wp-content/uploads/cicual/2-laboratory_animal_anaesthesia.pdf 10.3382/ps/pev342 Tamilselvan S, Dhote BS, Singh I, Mrigesh M, Sathapathy S, and Mahanta D. Gross morphology of testes and gonadosomatic index (GSI) of guinea fowl (Numida meleagris). J. Entomol. Zool. Stud. 2018; 6(3): 156-159. Available at: https://www.entomoljournal.com/archives/2018/vol6issue3/PartC/6-2-239-203.pdf Cameron AWN, and Tilbrook AJ. The rate of production of spermatozoa by rams and its consequences for flock fertility. In: Oldham, C.M., Martin, G.B., Purvis, I.W. (Eds.), Reproductive physiology of Merino sheep: Concepts and consequences, University of Western Australia, Crawley. 1990; 327. Available at: https://research-repository.uwa.edu.au/en/publications/reproductive-physiology-of-merino-sheep-concepts-and-consequences/ 10.1016/S0378-4320(98)00110-9 Okpe GC, Nwatu U, and Anya K. Morphometric study of the testes of the Nigerian local breed of chicken. Anim Res Int. 2010; 7(2): 1163-1168. DOI: 10.4314/ARI.V7I2 10.1098/rspb.2009.0134 10.1095/biolreprod39.5.1004 10.2141/jpsa.0150097 10.1038/nature02117 10.3390/agriculture13081620 10.3389/fendo.2012.00148 10.1016/j.ygcen.2025.114840 10.1016/j.theriogenology.2005.11.025