Endometritis in Dairy Cows: Classification, Diagnosis and Reproductive Consequences

Endometritis is one of the most important reproductive tract disorders affecting dairy cows during the postpartum period. Approximately one out of two intensively managed, high-producing dairy cows develop reproductive tract infection or inflammatory disease within 6 weeks after calving¹. The challenge for practitioners is distinguishing normal uterine recovery from inflammation that is likely to compromise fertility. 

Endometritis refers specifically to superficial inflammation of the endometrium, characterized by disruption of the luminal epithelium, vascular congestion, oedema, and inflammatory-cell infiltration without extending beyond the stratum spongiosum². It should be distinguished from metritis, which involves inflammation of all uterine layers³. 

Classifying Postpartum Uterine Disease 

Clinical assessment should consider both the timing and nature of vaginal discharge. 

Within the first 3 weeks after calving, red-brown, watery or purulent, often foetid vulvar discharge, with or without fever, is associated with metritis. This affects approximately 10%–20% of dairy cows³. 

Between 4 and 6 weeks postpartum, purulent material may be present in the vagina because of delayed uterine involution. When the source of the exudate is not confirmed as endometrial inflammation, it is classified as purulent vaginal discharge (PVD)⁴. Importantly, around half of PVD cases may occur without endometrial inflammation because the inflammation originates from the vagina, cervix, or both^4,5. 

When PVD is accompanied by endometrial inflammation, the condition is classified as clinical endometritis (CE). 

A cow without visible PVD is not necessarily free of uterine inflammation. Approximately 10%–40% of apparently healthy dairy cows may have inflammation detectable only through cytology². This is termed subclinical endometritis (SCE) or cytological endometritis. 

Practical Diagnosis in the Field 

Vaginal discharge remains an important practical indicator. PVD can be assessed using vaginoscopy, a gloved hand or a Metricheck device. Discharge is commonly scored from 0 to 3: 

• Score 0: clear mucus or no discharge 

• Score 1: mucus containing flecks of pus 

• Score 2: mucopurulent material containing less than 50% pus 

• Score 3: purulent material containing more than 50% pus or sanguineous material 

At the fourth week postpartum, score 3 is considered the relevant PVD cut-off, whereas from the fifth week onward, score 2 is used^2,4. 

Transrectal ultrasonography can complement vaginal examination by identifying uterine fluid and assessing its diameter and echogenicity. Fluid exceeding 2 cm with mixed echogenicity or worse between 4 and 6 weeks postpartum is associated with reduced relative pregnancy rates^6,7. 

For SCE, endometrial cytology is particularly useful. Samples can be obtained using a cytobrush, low-volume lavage or cytotape. Between 4 and 6 weeks postpartum, >5% polymorphonuclear leukocytes (PMN) relative to epithelial cells is typically used to identify SCE; when cytotape is collected at insemination, a ≥1% PMN cut-off is applicable². 

Reproductive Consequences² 

Endometritis can interfere with sperm transport and storage, oocyte maturation and ovulation, zygote development, implantation, and embryonic and foetal growth. Clinically, affected cows have a reduced probability of pregnancy at first insemination and may experience greater pregnancy losses or reduced pregnancy rates throughout lactation. 

The practical consequence is substantial: cows with endometritis may require approximately 30 additional days to become pregnant compared with unaffected cows. 

Clinical Takeaway 

For the practicing veterinarian, visible discharge alone should not define endometritis. PVD, CE and SCE represent different clinical presentations and require appropriate diagnostic approaches. Combining vaginal examination, ultrasonography and endometrial cytology provides a more reliable assessment than relying on a single finding, particularly when evaluating cows that appear clinically normal but have impaired reproductive performance. 

References 

1. LeBlanc, S. J. (2014). Reproductive tract inflammatory disease in postpartum dairy cows. Animal: An International Journal of Animal Bioscience, 8(Suppl 1), 54–63. https://doi.org/10.1017/S175173111 4000524 

2. Pascottini OB, Aurich C, England G, Grahofer A. General and comparative aspects of endometritis in domestic species: A review. Reproduction in domestic animals. 2023 Sep;58:49-71. https://onlinelibrary.wiley.com/doi/pdfdirect/10.1111/rda.14390 

3. Sheldon, I. M., Lewis, G. S., LeBlanc, S., & Gilbert, R. O. (2006). Defining postpartum uterine disease in cattle. Theriogenology, 65(8), 1516– 1530. https://doi.org/10.1016/j.theriogenology.2005.08.021 

4. Dubuc, J., Duffield, T. F., Leslie, K. E., Walton, J. S., & LeBlanc, S. J. (2010a). Definitions and diagnosis of postpartum endometritis in dairy cows. Journal of Dairy Science, 93(11), 5225–5233.https://doi.org/10.3168/jds.2010-3428 

5. Deguillaume, L., Geffré, A., Desquilbet, L., Dizien, A., Thoumire, S., Vornière, C., Constant, F., Fournier, R., & Chastant-Maillard, S. (2012). Effect of endocervical inflammation on days to conception in dairy cows. Journal of Dairy Science, 95(4), 1776–1783. https:// doi.org/10.3168/jds.2011-4602 

6. Kelly, E., McAloon, C. G., O'Grady, L., Duane, M., Somers, J. R., & Beltman, M. E. (2020). Cow-level risk factors for reproductive tract disease diagnosed by 2 methods in pasture-grazed dairy cattle in Ireland. Journal of Dairy Science, 103(1), 737–749. https://doi.org/10.3168/ jds.2019-17064 

7. Šavc, M., Duane, M., O'Grady, L. E., Somers, J. R., & Beltman, M. E. (2016). Uterine disease and its effect on subsequent reproductive performance of dairy cattle: A comparison of two cow-side diagnostic methods. Theriogenology, 86(8), 1983–1988. https://doi. org/10.1016/j.theriogenology.2016.06.018 

8. Wagener, K., Gabler, C., & Drillich, M. (2017). A review of the ongoing discussion about definition, diagnosis and pathomechanism of subclinical endometritis in dairy cows. Theriogenology, 94, 21–30. https://doi.org/10.1016/j.theriogenology.2017.02.005