Effect of Natural Photoperiod on Epididymal Sperm Quality and Testosterone Serum Concentration in Domestic Cat (Felis silvestris catus) R Nun˜ez-Favre, MC Bonaura, CM Tittarelli, D Mansilla-Hermann, RL de la Sota and MA Stornelli Facultad de Ciencias Veterinarias, Laboratorio de Reproduccio ´n Animal, Universidad Nacional de La Plata, La Plata, Argentina Contents The aim of this study was to assess epididymal sperm characteristics and serum testosterone concentration in cats under natural photoperiod. The hypothesis was that natural photoperiod induces seasonal changes in spermatozoal quality and serum testosterone concentration. Mixed breed tomcats (n = 43) that underwent bilateral orchiectomy at a municipal public pet shelter were used in the study. Epididymides were divided into two groups according to time of castration. In Group I, toms were castrated during increasing light (IL; [winter and spring; n = 24]), and group II, during decreasing light (DL; [summer and fall; n = 19]). Only mature toms castrated in the two lasts weeks of each season were included in this study. Sperm samples were obtained by cutting the cauda epididymis in Tris solution and tested for motility (MOT,% motile), velocity (VEL, 0–5), total sperm cells (TS, 10 6 ), acrosome integrity (ACR,% intact; FITC-PSA), plasma membrane integrity (MI,%intact; CFDA-PI) and sperm mor- phology (SM,% normal). Before orchiectomy, blood samples were taken to measure serum concentrations of testosterone (T2) by a solid-phase RIA. Data were analysed with the mixed procedure of SAS. Toms castrated during IL had higher sperm plasma membrane integrity and better sperm morphology compared to toms castrated during DL (69.0 ± 2.7 vs 60.6 ± 2.1, p < 0.01; 45.9 ± 2.5 vs 35.9 ± 3.4; p < 0.02; respec- tively) and tended to have higher sperm motility and total number of sperm cells compared to toms castrated during DL (56.3 ± 2.8 vs 47.3 ± 3.7, p < 0.06; 13.8 ± 1.4 vs 10.0 ± 1.8, p < 0.09). However, velocity, acrosome integrity and serum testosterone concentrations were similar between both groups (3.5 ± 0.1 vs 3.4 ± 0.1, p > 0.6; 45.8 ± 3.3 vs 44.0 ± 4.0, p > 0.72; 0.76 ± 0.15 vs 0.59 ± 0.19, p > 0.51; respectively). In conclusion, natural photoperiod induces seasonal changes in sperm quality with a moderate variation in serum testos- terone concentrations. Introduction The queen is a seasonal breeder when exposed to natural photoperiod, with ovarian activity ceasing under decreasing photoperiod and resuming with increasing photoperiod. This seasonality may be observed in both females and males of several mammalian species, and in these species, photoperiod and melatonin concentra- tions are related to circannual sperm production (Chemineau et al. 2008). This seasonality is observed in geographic locations where large differences between hours of light during the year are present and occurs as an adaptation to annual changes in the habitat (Malp- aux et al. 2001; Chemineau et al. 2008). Although the reproductive features of queens are well known, in tom cats, there are few studies about sperm production. Likewise, the effect of season on reproductive function in the male domestic cat has been insufficiently explored. Whereas previous studies concluded that male cats are not seasonal in sperm production (Spindler and Wildt 1999; Franca and Godinho 2003), more recent studies challenge those findings and suggest seasonality of sperm production (Axner and Linde Forsberg 2007; Blottner and Jewgenow 2007; Stornelli et al. 2009). Previous studies have shown seasonal changes in testic- ular cell morphology in domestic cats (Stornelli et al. 2009). Probably, these changes are reflected in seasonal variations of epididymal sperm quality. In the same way, seasonal mammals show changes in testosterone serum concentrations during the year related to sperm produc- tion and cycles of testicular growth and involution (Johnstone et al. 1984; Blottner and Jewgenow 2007). The aim of this study was to assess epididymal sperm characteristics and serum testosterone concentration in cats under natural photoperiod. Our hypothesis was that natural photoperiod induces seasonal changes in sper- matozoa quality and serum testosterone concentration. Materials and Methods Forty-three privately owned short-hair mixed breed male cats aged between 1 and 5 years were included in this study. The cats were included in a programme for breeding control at the Municipal Public Pet Shelter of the City of La Plata. Before surgery, all animals were anesthetized with a combination of ketamine (25 mg/kg im; Vetanarcol ® , Laboratorios Koning SA, Avellaneda, Buenos Aires, Argentina), xylazine (1 mg/kg im; Sedo- min ® , Laboratorios Koning SA, Avellaneda, Buenos Aires, Argentina). After surgery, all animals were medicated for 3 days with amoxicillin (22 mg/kg im, Clamoxyl LA, Laboratorio Pfizer SRL, Ciudad Auto´n- oma de Buenos Aires, Argentina) and tramadol (1 mg/ kg im; Algen ® Laboratorio Richmond SA, Grand Bourg, Buenos Aires, Argentina). All surgical proce- dures were performed by a licensed veterinarian and followed approved guidelines for ethical treatment of animals (CIOMS 1985). To show the true effect of season, only toms castrated during the two lasts weeks of each season were included in the study (winter: second and third weeks of September [09/06/10 to 09/20/ 10]; spring: second and third weeks of December [12/06/ 10 to 12/20/10]; summer: second and third weeks of march [03/06/10 to 03/20/10]; fall: second and third weeks of June [06/06/10 to 06/20/10]). Hence, according the time of castration, epididymides were divided into two groups. Group I toms were castrated during increasing light (IL; [winter and spring; IL, n = 24]), and group II toms were castrated during decreasing light (DL; [summer and fall; IL, n = 24]). After orchiectomy, each testis with adjacent epididymis was transported to © 2012 Blackwell Verlag GmbH Reprod Dom Anim 47 (Suppl. 6), 232–234 (2012); doi: 10.1111/rda.12050 ISSN 0936–6768