Dexamethasone's effect on endometrial inflammatory response in jennies after artificial insemination with frozen donkey semen

Abstract

Artificial insemination (AI) with frozen donkey semen leads to low fertility rates in jennies. This might be due to an exacerbation of the acute inflammatory endometrial response to frozen semen, as seen in mares with persistent post breeding endometritis. Higher pregnancy rates were obtained in these mares when treated with dexamethasone at breeding time. The aim of this study was to evaluate the effect of dexamethasone on endometrial inflammatory responses in jennies after AI with frozen donkey semen. This study was performed from August to December 2022 in Argentina. Six healthy jennies of proven fertility were included in a crossover experimental design. All animals passed through an estrous cycle with no treatment before crossover between treatments. Jennies were subjected to 1) no AI and no treatment in estrus (control, C); 2) AI with no treatment (D-); and 3) AI with administration of dexamethasone, 50 mg IV at AI time (D+). Post ovulation. deep AI was performed with frozen donkey semen (700 × 106 progressively motile sperm (PMS). Endometrial samples (cytology and biopsies) were taken at estrus and 24 hours post AI. Cytology smears were stained with Diff-Quick™; 200 cells were counted under an optical microscope (Nikon Eclipse™ NI-U) and the percentage (%) of polymorphonuclear neutrophils (PMN) and eosinophils was calculated.Endometrial biopsies were taken from the bifurcation of the uterine body, fixed in 10% buffered formalin prior to hematoxylin-eosin staining. Five fields were selected per sample at 400x and average cell counts were calculated. The effect of treatments on % PMN and % eosinophils in cytology and biopsies were evaluated by the Kruskal Wallis test followed by the Dunn test for multiple comparisons. Values are expressed as median and interquartile ranges. The cytology smears of all animals showed an inflammatory response to semen deposition. There were differences (P = 0.003) between % PMN in C [0.625 (0.50 - 0.94)] and the other two groups [D-: 35.00 (22.50 - 46.00); D+: 39.50 (28.63 - 40.25)]. No eosinophils were observed. The inflammatory pattern in biopsies showed a diffuse infiltration of PMN and eosinophils in the luminal epithelium, stratum compactum and stratum spongiosum. There were differences (P = 0.003) between % PMN in C [0.30 (0.05 - 0.40) and the other two groups [D-: 41.90 (28.60 - 43.50); D+: 28.70 (10.35 - 49.00)]. Eosinophils were different (P = 0.005) for the three groups [C: 0.40 (0.20 - 1.20); D-: 21.50 (11.35 - 60.60); D+: 4.60 (1.30 - 7.75)]. In conclusion, a single dose of dexamethasone at AI in jennies did not decrease endometrial PMN but decreased eosinophils 24 hours after insemination.