Quantitative and functional dynamics of circulating and endometrial polymorphonuclear leukocytes in healthy peripartum dairy cows

The aim of the present study was to assess the counts, viability, and functionality of circulating and endometrial polymorphonuclear leukocytes (PMN) isolated from fourteen clinically and metabolically healthy multiparous dairy cows in the peripartum period. For this, blood samples were collected at -5, +9, +21 and + 37 days (d) relative to calving. Cytology samples were collected from the vagina, cervix, and uterus at +9, +21 and + 37 d, using the cytobrush technique. Additional vaginal samples were collected at -5 d. Cytology smears were prepared and the PMN-to-all nucleated cell proportions (PMN%) were calculated. The endometrial cytobrush samples were also used for flow cytometric assessment of endometrial PMN (ePMN) viability and functionality. Functionality tests for circulating PMN (cPMN) included phagocytosis (PC), oxidative burst, and intracellular proteolytic degradation. For ePMN, we evaluated PC only. The effect of day relative to calving on PMN viability and functionality were fitted in linear regression models, accounting for repeated measures. The endometrial PMN% were higher at +9 d (23.5 ± 0.4%; least-squares means ± standard error) and +21 d (8.5 ± 0.3%) than at +37 d (1.4 ± 0.3%). No changes in PMN% were found on either vaginal or cervical cytology along the peripartum period. The cPMN counts were higher pre- (6.2 ± 0.4 x 10⁶/mL) than postpartum (4.9 ± 0.4 x 10⁶/mL). Upon viability analysis, only the percentage of viable cPMN tended to be lower at -5 d (90.1 ± 1.5%) than at +37 d (94.1 ± 1.4%), and no other changes in the percentage of apoptotic and necrotic cPMN, nor in their functionality were found during the peripartum period. Analysis of ePMN viability showed that the percentage of viable ePMN did not change over time. In marked contrast, the percentage of apoptotic ePMN was higher at +9 d (37.8 ± 5.1%) than at +21 d (20.9 ± 5.1%) and +37 d (11.9 ± 5.3%), while the percentage of necrotic ePMN was lower at +9 d (27.0 ± 6.3%) than at +37 d (54.9 ± 6.6%). The percentage of ePMN PC was higher at +9 d (27.5 ± 3.4%) than at +37 d (13.3 ± 4.9%). In conclusion, during the peripartum period ePMN in the healthy postpartum uterus are highly dynamic in terms of counts, viability, and functionality compared to their circulating counterparts.

Flow Cytometric Assessment of the Viability and Functionality of Uterine Polymorphonuclear Leukocytes in Postpartum Dairy Cows

Postpartum dairy cows experience impaired peripheral polymorphonuclear leukocyte (PMN) functionality, which has been associated with reproductive tract inflammatory diseases. However, it has not been elucidated yet whether endometrial PMN functionality is (equally) impaired. We developed a method for endometrial PMN isolation and flow cytometric assessment of their viability and functionality. We also evaluated PMN immunolabeling, using a specific bovine granulocyte marker, CH138A. Blood and endometrial cytobrush samples were collected in duplicate from seventeen clinically healthy Holstein-Friesian cows between 9 and 37 days in milk. The proportion of viable, apoptotic, and necrotic PMN in endometrial samples roughly ranged from 10 to 80%, indicating highly dynamic endometrial PMN populations in the postpartum uteri. Endometrial PMN functionality testing revealed that PMN immunolabeling increased the accuracy, although this protocol might influence the median fluorescence intensity of the sample. Phagocytosis seemed the most stable and reliable endometrial PMN function and could be assessed satisfactorily without prior CH138A immunolabeling. However, the interpretation of oxidative burst and intracellular proteolysis tests remains challenging. The correlation between peripheral and endometrial PMN functionality was poor. Further research is warranted to unravel the role of uterine PMN viability and functionality in bovine uterine health.

Association of metabolic markers with neutrophil function in healthy postpartum dairy cows

The objective of this study was to evaluate the associations of serum markers for systemic inflammation, liver, mineral, and energy status, and blood neutrophil counts with the function of circulating neutrophils in postpartum dairy cows. Blood samples were collected from 21 healthy Holstein cows at 5, 10, 14, and 21 d postpartum. Serum samples were used to measure concentrations of total calcium, phosphorus, magnesium, total protein, albumin, globulin, cholesterol, urea, glucose, gamma-glutamyl transferase, aspartate aminotransferase, glutamate dehydrogenase, haptoglobin (Hp), β-hydroxybutyrate, non-esterified fatty acids (NEFA), and insulin-like growth factor-1. The shift of percentage of activated neutrophils for phagocytosis (PPC) and oxidative burst (POB) and the median fluorescence intensity (MFI) for PC (MFIPC), OB (MFIOB), and endocytic and proteolytic degradation measured via DQ-ovalbumin (MFIDQ) were evaluated using flow cytometry. Mixed linear regression models were used to assess the associations of serum concentrations of metabolites and blood neutrophil counts with each neutrophil function assay outcome accounting for d postpartum, parity, and body condition score. Pearson correlation tests (r) were used to describe the relationships of metabolites and neutrophil counts with neutrophil function assays that were significant in the regression models. Greater serum concentrations of Hp were associated with lesser OB function (POB and MFIOB; r = -0.2 for both), but greater PPC and MFIDQ (r = 0.3 for both). Greater serum NEFA and cholesterol were associated with lesser (r = -0.3) and greater (r = 0.2) POB function, respectively. Blood neutrophil counts were associated with PPC (r = -0.2) and MFIDQ (r = -0.3). At 5 d postpartum, greater serum total protein was associated with greater OB function (POB and MFIOB; r = 0.4 for both). Other markers were not associated with neutrophil function. Some metabolic and inflammatory markers in healthy postpartum dairy cows were associated with circulating neutrophil function. However, these associations only explained a small proportion of the variance in neutrophil function. Serum Hp concentration was most associated with neutrophil function changes but had opposite directions of association with OB- and PC-related functions. Future studies should focus on understanding the mechanisms by which Hp and other metabolic indicators affect neutrophil function in healthy and diseased postpartum dairy cows.

Effect of anti-inflammatory treatment on systemic inflammation, immune function, and endometrial health in postpartum dairy cows

Systemic inflammation (SI) is increasingly studied in several species because it may be central in many metabolic disturbances and be a risk factor for clinical disease. This proof-of-concept study evaluated the effects of the anti-inflammatory drug meloxicam on markers of SI and energy metabolism, polymorphonuclear neutrophil (PMN) function, and endometritis in clinically healthy postpartum dairy cows. Cows received meloxicam (0.5 mg/kg of body weight; n = 20) once daily for 4 days (10-13 days postpartum) or were untreated (n = 22). Blood samples were collected -7, 1, 3, 5, 7, 10, 11, 12, 13, 14, 18, 21, 28, and 35 days relative to calving to measure serum concentrations of metabolic and inflammatory markers. Function of peripheral blood PMN were evaluated at 5, 10, 14, and 21, and proportion of PMN in endometrial cytology were performed at 5, 10, 14, 21, 28 and 35 days postpartum. Meloxicam decreased serum haptoglobin from the second until the last day of treatment, and improved indicators of energy metabolism (lesser β-hydroxybutyrate and greater insulin-like growth factor-1 during treatment, and greater glucose at the end of treatment than control cows). This improved PMN function at 14 days postpartum, but the endometrial inflammatory status was not affected.