Evaluation of Prolonged Endometrial Inflammation Associated with the Periparturient Metabolic State in Dairy Cows

SIMPLE SUMMARY: The appearance of endometrial polymorphonuclear cells (PMN) was sequentially observed after calving by endometrial cytology, and the relationship between endometrial inflammation and metabolic state during the peripartum period was evaluated. The endometrial inflammation threshold was determined as 5.0% PMN according to PMN dynamics revealed by endometrial cytology. The present study demonstrated that cows with low body condition scores and backfat thickness had prolonged endometrial inflammation; moreover, higher blood 3-methylhistidine after calving was observed in cows with prolonged endometrial inflammation, indicating that muscle breakdown was promoted in those cows. Hence, it was proposed that evaluating body fat reservation and muscle breakdown was crucial for understanding endometrial inflammation convergence in lactating dairy cows. ABSTRACT: The objectives of this study were to assess the sequential dynamics of the endometrial polymorphonuclear cells (PMN) after calving by endometrial cytology, and clarify the factors that cause prolonged endometrial inflammation in lactating dairy cows. A total of 33 lactating Holstein dairy cows were used from −4 to 8 wk relative to calving (0 wk: the calving week). Endometrial samples were obtained sequentially from 2 to 8 wk. Body condition score and backfat thickness were obtained weekly from −4 to 8 wk. Blood samples collected from −4 to 8 wk were analyzed for indicators of energy status, hepatic function, systemic inflammation, and calcium. Blood amino acids were measured at 2 wk. Daily milk production was determined between 5 and 65 d postpartum. Based on the sequential cytological analysis, the endometrial inflammation threshold was set at ≥5.0% PMN, and the median wk of PMN% lower than 5.0% was 4.5 wk in this study; therefore, we classified the cows into the early group (cows with endometrial inflammation converged within 4 wk: n = 17) and the late group (cows with endometrial inflammation converged at or after 5 wk: n = 16). There were no differences in daily milk production, energy status, hepatic function, blood calcium concentration, and systemic inflammatory response. The late group had lower body condition scores and backfat thickness during the experimental period, and a higher blood concentration of 3-methyl histidine, indicating muscle breakdown, was observed in the late group at 2 wk. Our findings indicated that the lack of body fat reservation during the peripartum period and the increased muscle breakdown after calving were risk factors for prolonged endometrial inflammation.