Feline leukemia virus (FeLV) infection is considered one of the most serious disease threats for the endangered Iberian lynx (Lynx pardinus) Over 14 years (2008–2021), we investigated FeLV infection using point-of-care antigen test and quantitative real-time TaqMan qPCR for provirus detection in blood and tissues in lynxes from Andalusia (Southern Spain). A total of 776 samples from 586 individuals were included in this study. The overall prevalence for FeLV antigen in blood/serum samples was 1.4% (5/360) (95% CI: 0.2–2.6), FeLV proviral DNA prevalence in blood samples was 6.2% (31/503) (95% CI: 4.1–8.6), and FeLV proviral DNA in tissues samples was 10.2% (34/333) (95% CI: 7–13.5). From a subset of 129 longitudinally sampled individuals, 9.3% (12/129) PCR-converted during the study period. Our results suggest that FeLV infection in the Andalusian population is enzootic, with circulation of the virus at low levels in almost all the sampling years. Moreover, since only one viremic individual succumbed to the infection, this study suggests that lynxes may therefore control the infection decreasing the possibility of developing a more aggressive outcome. Although our results indicate that the FeLV infection in the Iberian lynx from Andalusia tends to stay within the regressive stage, continuous FeLV surveillance is paramount to predict potential outbreaks and ensure the survival of this population.

The Iberian lynx (Lynx pardinus), once considered the most endangered felid, has shown demographic recovery thanks to intensive conservation measures. Over the past two decades, large physiological datasets have supported both clinical management and research, yet thyroid function has remained comparatively underexplored. This study provides the first reference intervals (RI) for total thyroxine (TT4) and thyroid-stimulating hormone (TSH) in captive and wild lynxes, and assesses the effects of age, sex, and environment. Serum samples from 71 individuals (32 captive, 39 wild; 32 females, 39 males) were analysed, including 32 young adults, 14 adults, and 25 geriatric animals. TT4 was measured by enzyme immunoassay, and TSH using chemiluminescence. TT4 RI was 0.80–2.00 µg/dl (captive) and 0.70–2.20 µg/dl (wild) (p = 0.065). TSH RI was 0.00–1.10 ng/ml (captive) and 0.00–0.10 ng/ml (wild), showing a significant difference (p < 0.001). Captive males had higher TT4 than females (p = 0.018), while no sex difference appeared in wild lynxes (p = 0.408). Age had no significant effect on TT4 (p = 0.462) or TSH (p = 0.739). Findings confirmed that environment and sex (captivity) influenced thyroid parameters, while age did not. These values are crucial for health monitoring and endocrine assessment in this endangered species.