Postpartum Uterine Involution in Cows: Quantitative Assessment of Structural Remodeling and Immune Cell Infiltration.

Postpartum uterine involution in cattle involves complex morphological and immunological changes essential for restoring uterine health and fertility. This study evaluated endometrial biopsies collected at four postpartum time points to characterize tissue remodeling and immune cell dynamics during involution. Histology revealed intact luminal columnar epithelium in 92.98% of samples, with stable stromal architecture. Stromal edema decreased by Day 7 but increased again by Day 35, while endometrial gland numbers significantly rose at Day 35, suggesting glandular recovery linked to resumed cyclicity. Subepithelial collagen deposition peaked on Day 21, indicating active extracellular matrix remodeling. Immunologically, early postpartum was marked by increased PMNs and macrophages, whereas Day 21 showed peak infiltration of natural killer (NK) cells and T and B lymphocytes, sometimes forming lymphoid aggregates. Manual and automated immune cell quantifications correlated well. These findings demonstrate a dynamic shift from acute neutrophil-dominated inflammation to a lymphocyte-rich environment during uterine involution. This immune modulation may contribute to the earlier diagnosis of subclinical endometritis, typically identified at later stages of postpartum period. Overall, this study provides insight into the temporal immunomorphological events supporting uterine recovery, with potential implications for reproductive management in dairy cattle.