The reproductive impact and predictive biomarkers of purulent vaginal discharge in dairy cows

Inflammation of the bovine uterus in the post-partum period is common. However, a proportion of cows fail to resolve this inflammation by 21 days post-partum (DPP), resulting in cows presenting with purulent vaginal discharge (PVD). PVD inhibits reproductive efficiency in dairy cows internationally however its effects on dairy cows in the Irish pasture-based grazing system are unclear. Our group previously identified that 7 DPP is an important time point in the development of uterine disease. Therefore, we hypothesise that PVD leads to sub-optimal levels of reproduction in the Irish dairy herd and that markers of inflammation at 7 DPP that can predict cows that will present with PVD at 21 DPP. To determine the effects of PVD, a total of 440 mixed-parity Holstein-Friesian dairy cows were assessed for PVD at 21 DPP by vaginal mucus scoring (VMS). Cattle were classified as healthy (VMS 0; clear or no vaginal exudate) or as having PVD (VMS 1-3; presence of purulent material in the vaginal exudate). The 305-day milk kg, milk protein kg and milk fat kg yield prior to and after disease diagnosis, services per conception and the calving-conception period (CCP) were recorded. Healthy cows and cows with PVD had similar milk component yield. Cows with PVD had an 9 day longer calving interval and a 34% higher risk of having a longer calving interval than healthy cows. Odds ratio analysis determined that cows with PVD were more likely to fail to conceive and to have lower conception rates than healthy cows. Cows were retrospectively categorised with “low” or “high” milk yield based on being above or below the median 305-day milk kg yield of the study population (6571 kg) in the lactation prior to vaginal mucus scoring. “High” yielding cows were more likely to present with PVD on 21 DPP, to have impaired fertility and a significantly longer in cows PVD than their healthy counterparts. We hypothesised that the circulating concentrations of vitamin D, a potent immunomodulator, are lower in cows with PVD at 7 DPP and are correlated with the acute phase protein alpha-1 acid glycoprotein (AGP) and metabolites ( ß-hydroxybutyrate (ßHB), NEFA and glucose). In total, concentrations of the vitamin D metabolite 25(OH)D3 in 557 mixed-parity Holstein-Friesian at pre-calving, calving, 7 DPP and 21 DPP were measured in blood samples. The only significant difference found was at 7 DPP where healthy cows had higher circulating 25(OH)D3 concentrations than cows with PVD. In high yielding cows, there were no 25(OH)D3 concentration variances between healthy cows and cows with PVD at any timepoint. The 7 DPP concentrations of AGP, ßHB, NEFA and glucose were similar between healthy cows and cows with PVD and there were no correlations between 25(OH)D3 and any marker in healthy cows or cows with PVD. These results reveal that although vitamin D did not modulate the inflammatory markers at 7 DPP, it is apparent that elevated vitamin D consumption occurs in cows with subsequent PVD at this stage. With this knowledge, we hypothesised that a single or a panel of prognostic biomarkers that can accurately predict the onset of PVD is obtainable at 7 DPP. We included the relative abundance of 5 reproductive tract bacterium that are known to be highly expressed in cows with PVD, the quantities of 37 glycoforms of Immunoglobulin G and previous markers for a total of 54 biomarkers. Accuracy was determined using receiver operative characteristic (ROC) curves. At 7 DPP, a combination of IgG glycoforms 6 and 9 could identify cows with PVD at 21 DPP (AUC=0.77). The same combination could distinguish between healthy cows and cows with PVD (AUC=0.88) with an above median 305-day milk yield in the previous lactation. Our results yielded a biomarker combination with an effective ability to identify cows at 7 DPP that will present with PVD at 21 DPP. This promising finding will have positive implications for future herd health and welfare.