Prolonged glucocorticoid administration affects oocyte morphology in cats (Felis catus) undergoing an ovarian stimulation protocol.

While captivity-related stress and the associated rise in baseline glucocorticoid (GC) concentrations have been linked to ovarian quiescence in some felid species, no study has examined the effects of elevated GC on oocyte quality. This study examined the effects of exogenous GC administration on the ovarian response and oocyte quality of domestic cats after an ovarian stimulation protocol. Entire mature female cats were divided into treatment (n = 6) and control (n = 6) groups. Cats in the GC treatment (GCT) group were given 1 mg kg-1 oral prednisolone daily from Day 0-45. All cats (n = 12) were given 0.088 mg kg-1 day-1 progesterone orally from Day 0-37, before treatment with 75 IU eCG im to induce follicular growth on Day 40, followed by 50 IU hCG im 80 h later to induce ovulation. Cats were ovariohysterectomised 30 h after the hCG treatment. Blood samples were collected on Days 0, 10, 30 and 40 (prior to eCG treatment), 80 h after eCG treatment, and on Day 45 for cortisol, glucose, prednisolone, oestradiol, and progesterone analysis. Cortisol concentrations did not differ between treatment groups throughout the study. Mean glucose concentrations were higher in the GCT cats (P = 0.004). Prednisolone was undetectable in all samples. Oestradiol and progesterone concentrations confirmed that the eCG treatment stimulated follicular activity and ovulation in all cats. Following ovariohysterectomy, the ovarian responses were graded (1 = excellent, 4 = poor) and oocytes retrieved from the oviducts. Each oocyte was given a total oocyte score (TOS: using an 9-point scale, 8 = best) based on four parameters: oocyte morphology, size, ooplasm uniformity and granularity, and zona pellucida (ZP) thickness and variation. Ovulation was confirmed in all cats, with a mean of 10.5 ± 1.1 ovulations per cat. Ovarian mass, ovarian response, number of ovulations, and oocyte recovery did not differ between groups. Oocyte diameter did not differ between the groups, but the ZP was thinner in the GCT group (3.1 ± 0.3 µm vs. 4.1 ± 0.3 µm, P = 0.03). The TOS was similar between treatment and control cats, but the ooplasm grade was lower (1.5 ± 0.1 vs. 1.9 ± 0.1, P = 0.01) and there was a tendency for ZP grade to be poorer (0.8 ± 0.1 vs. 1.2 ± 0.2; P = 0.08) in the treatment group. In conclusion, the GC treatment resulted in morphological changes to oocytes collected following ovarian stimulation. Whether these changes would affect fertility warrants further investigation.

Exogenous glucocorticoid treatment affects Sertoli cell load and epididymal sperm quality in domestic cats (Felis catus).

Elevated glucocorticoid (GC) concentrations associated with captivity-related stress have been linked to impaired testicular function and low sperm quality in felids, but direct physiological evidence is lacking. This study assessed the effects of exogenous GC treatment on felid testicular function using the domestic cat (Felis catus) as a model species. Sixteen intact male cats aged 2.4 ± 0.8 years (mean ± SEM) were divided randomly into treatment (n = 8) and control (n = 8) groups. Treatment cats were given 1 mg kg-1 oral prednisolone daily for 50 days. Blood samples were taken on Days 0 (first prednisolone treatment), 2, 4, 7, 10, 20, 30, 40, 50 (prior to neutering) and 60 of the trial. All cats were orchiectomised on day 50, epididymal sperm assessed, and the testes fixed for histological assessment. Testosterone concentrations did not differ between the two groups. While sperm motility was similar between the treatment and control groups, cats given prednisolone had a higher proportion of morphologically abnormal sperm in both the caput (72.5% vs. 59.6%, P < 0.001) and cauda (56.7% vs. 35.8%, P < 0.001) epididymis. Testicular histomorphometric data and total number of germ cells per seminiferous tubule cross section did not differ between groups, nor did the relative abundance of spermatogonia, spermatocytes, and spermatids. Cats given prednisolone had fewer Sertoli cells per tubule cross-section than those in the control group (17.1 ± 0.9 vs. 19.7 ± 0.8, P = 0.04), which was likely related to higher rates of Sertoli cell apoptosis in treatment versus control cats (0.25 ± 0.02 vs. 0.10 ± 0.02 apoptotic Sertoli cells per tubule, respectively; P < 0.001). Sertoli cell load (number of germ cells per Sertoli cell) was also higher in the treatment group than in the control group (11.5 ± 0.8 vs. 9.4 ± 1.2 germ cells per Sertoli cell, respectively; P < 0.001), and was positively correlated with the percentage of morphologically abnormal sperm in the epididymis (r2 = 0.78, P < 0.001). Prednisolone treatment resulted in an increase in the proportion of abnormal sperm in the epididymis, which may be explained by an increased nurturing demand on a reduced Sertoli cell population. These findings provide novel evidence to support the hypothesis that elevated GC concentrations, such as those resulting from captivity-related stress, have the potential to impair testicular function and sperm quality in felids.