Monitoring Uterine Health (MUH)

Summary

• on average 3 out of 10 cows suffer from Subclinical Endometritis
• it often goes undetected as there are no typical uterus infection symptoms
• the infection can lead to poor conception rates and infertility

 

Subclinical (Cytological) Endometritis

Subclinical endometritis (also called cytological endometritis) is an inflammatory process of the bovine uterus without the typical symptoms of inflammation and without any involvement of pathogens. However, since the disease is highly correlated with poor fertility, dairy cows suffering from subclinical/cytological endometritis usually show poor conception rates. In the postpartum (p.p.) period, some cows typically develop clinical endometritis, which usually entails symptoms such as vaginal mucopurulent discharge. The rest of the herd appears healthy.

However, it is known that approx. 30% of the herd suffer from the subclinical endometritis, which often remains undetected, but results in poor fertility such as reduced pregnancy rates, increased median days open and diminished first service conception rates (1).

 

Etiology of subclinical/cytological endometriti

Etiology of subclinical endometritis has not been fully clarified yet. Recent studies suggest a multifactorial induction, leading to an inflammation of the endometrium. On the one hand, the inflammatory process could be induced by a foregoing bacterial infection. Although all pathogens have been cleared, the uterine immune response persists due to a disbalanced level of pro- and antiinflammatory cytokines. On the other hand, it is hypothesized that oxidative stress, negative energy balance or ketosis promote the occurrence of subclinical endometritis (2, 3).

 

Symptoms of subclinical/cytological endometritis

Subclinical endometritis often goes undetected as there are no typical uterus infection symptoms. In contrast to clinical/acute or chronical endometritis, there is no mucopurulent discharge, nor any visible signs of uterine inflammation that can be detected via vaginoscopy or ultra sound examination. The imbalance of the uterine immune response can only be diagnosed by endometrial cytology, which is why the disease is also called cytological endometritis (8). Another indicator for subclinical endometritis can be the conception rates as the disease is known to cause infertility. Hence, poor first service conception rates, a herd average with significantly more than 100 days open and reduced pregnancy rates can be a symptom of subclinical endometritis (1, 4).

 

Monitor uterine health: Diagnosis of subclinical endometritis

In the past, several techniques have been used to diagnose subclinical endometritis in cattle (6). Nowadays, endometrial cytology with microscopic analysis has become the gold standard. To obtain cytological material of the endometrium, samples can be retrieved by uterine lavage, uterine biopsy or by taking endometrial smears with a cytobrush or cytotape. Recent studies suggest cytobrush or cytotape is the most feasible approach (5, 9). For sampling, cytotape or cytobrush is induced into the cow’s uterus (e.g. during artificial insemination or fertility checkup) and gently rotated against the endometrial wall. The cytological sample is then spread onto a conventional microscopy slide, stained and examined under a microscope in order to define the rate of polymorphnuclear cells (PMNs) to epithelial cells, e.g. the relation of normal endometrial cells to inflammatory cells. After day 28 p.p., a healthy cow should have less than 5% PMNs in an endometrial smear. A level of more than 5% PMNs is defined as subclinical or cytological endometritis, implying the ongoing inflammatory process (7).

However, the traditional diagnostic procedures entail several challenges as they rely on manual microscopes, which are heavy and expensive. Furthermore, complex and time-consuming sample preparation and evaluation is required. Hence, subclinical endometritis diagnostics usually requires a specialized lab and experienced staff. A diagnosis is confirmed several days after sampling, which means that potential treatments or measures can only be established with a few days delay.