Cervical Neutrophil Infiltration in Relation to Macroscopic Cervix Appearance, Cytological Endometritis, and Reproductive Stage in Postpartum Grazing Dairy Cows

The bovine cervix undergoes endocrine-dependent physiological changes that may influence local immune activity and complicate the interpretation of cervical inflammation. This study evaluated the relationships among macroscopic cervical appearance, cervical neutrophil infiltration, reproductive stage, and endometrial inflammation in postpartum grazing dairy cows. Non-pregnant lactating Holstein × Jersey crossbred cows (n = 80) ≥ 45 days in milk underwent reproductive examination, cervical video-endoscopy, ultrasonography, cervical and endometrial cytology, and serum progesterone determination. Macroscopic cervical appearance was classified as C0, C1, or C2, whereas cervical polymorphonuclear neutrophil (PMN) percentage was analyzed as the primary proportional outcome using adjusted fractional logistic regression. A ≥5% cervical PMN threshold was used operationally for secondary analyses. C0, C1, and C2 occurred in 30.0%, 50.0%, and 20.0% of cows, respectively, and 20.0% had cervical PMN ≥ 5%. Macroscopic cervical appearance was not associated with cervical PMN percentage (p = 0.931) or cervical PMN ≥ 5% (p = 1.000). Cervical PMN percentage was higher in follicular-stage than in luteal-stage cows (p < 0.001). This association persisted after adjustment for parity and cytological endometritis using fractional logistic regression (β = 2.42; 95% CI, 0.81–4.03; p = 0.003), with an adjusted marginal difference of 10.48 percentage points (95% CI, 1.42–19.54; p = 0.023). A complementary two-part analysis supported this association, showing higher odds of detectable cervical PMNs (OR = 4.71; 95% CI, 1.73–12.82; p = 0.002) and higher mean PMN proportions among positive observations (mean ratio = 4.11; 95% CI, 1.40–12.06; p = 0.010) during the follicular stage. In secondary Firth penalized logistic regression, follicular stage remained associated with cervical PMN ≥ 5% (aOR = 5.38; 95% CI, 1.39–20.83; p = 0.015). Cervical and endometrial PMN percentages were weakly positively correlated (ρ = 0.240; p = 0.033), while agreement between cervical PMN ≥ 5% and cytological endometritis was limited (κ = 0.258). Neither cervical neutrophil infiltration nor cytological endometritis was associated with subsequent pregnancy, whereas serum progesterone concentration showed a positive exploratory association with pregnancy. Cervical neutrophil infiltration is associated with reproductive stage independently of parity and cytological endometritis, without relying on an unvalidated diagnostic threshold. Cervical cytology should therefore be interpreted within the reproductive and physiological context of the cow.