Recent studies in sheep, a short day seasonal breeder, have revealed that functional remodelling of the microvasculature of the pituitary gland is under seasonal regulation. As for other tissues, angiogenesis and vascular permeability in the ovine pituitary is controlled by pro-angiogenic (VEGF165a) and anti-angiogenic (VEGF165b) isoforms of Vascular Endothelial Growth Factor. Surprisingly, pituitary VEGF165b expression was found to be upregulated during the non-breeding season (NBS), corresponding to a reduction in the number of vascular loops. Here, we investigated the expression of these isoforms in the pars tuberalis (PT) and pars distalis (PD) of the pituitary gland of a long day breeder, using gonadal intact (stallions) and orchidectomised (geldings) Thoroughbred horses during the breeding season (BS) and NBS. Expression of VEGF isoforms was examined by double immunohistochemistry. Statistically significant effects of season, gonadal status and the interaction between them were observed in both regions of the pituitary. In the PD, an increase in VEGF165a was detected in stallions during the NBS (p<0.001). Conversely, the expression of VEGF165b in this region was increased during the BS (p<0.001). These results corroborate original findings in sheep. However, in the absence of the gonads, seasonal changes in VEGF165a expression were opposite to those recorded in intact animals, with robust up-regulation in the PD of geldings during the BS (p<0.001). In the PT, increased expression of both VEGF isoforms (VEGF165a, p<0.001; VEGF165b, p<0.05) was observed in geldings during the BS. These seasonal changes were counteracted by the presence of the gonads, resulting in a pattern similar to that observed in the stallions PD. Collectively, these findings show that VEGF isoform expression in the pituitary gland of photoperiodic mammals is highly sensitive to seasonal regulation, and that this mechanism for vascular remodelling is modulated by gonadal feedback to adjust to the physiological requirements of the species.