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Endometritis in the mare still constitutes a great problem in the management of broodmares. Inflammatory processes of the equine uterus can be classified as acute, chronic or subclinical endometritis. All these conditions may cause substantial reductions of a mare’s fertility. In recent years the problem of subclinical inflammatory processes with hidden or subtle clinical signs became more obvious.
Although several diagnostic methods such as rectal palpation, transrectal ultrasonography, vaginal examination, uterine culture, cytology or endometrial biopsy are available, the correct diagnosis of subclinical endometritis challenges practitioners in the field. Therefore, the overall objective of this study was to evaluate the ability, the reliability and the representativeness of the commonly used diagnostic techniques endometrial swab, cytological brush and endometrial biopsy to diagnose subclinical endometritis in mares. In the first study bacteriological, cytological and histological samples were taken from 55 mares without clinical signs of endometritis.
A double-guarded uterine swab (US), a singleguarded cytological brush (CB) and an endometrial biopsy (EB) were taken consecutively under manual control, smeared on microscopic slides for cytological examination and cultured for bacterial growth. Additionally, endometrial biopsy samples were evaluated for polymorphonuclear neutrophils (PMN) in the stratum compactum by a histopathological institute.
Bacteriological cultures and cytological samples were classified as negative (no uterine pathogens in monoculture; < 2% PMN) or positive (uterine pathogens in > 90% of the grown colonies; > 2% PMN) for endometritis. Uterine pathogens were found in 20.0% of the mares. Isolation of pathogens was not associated with positive cytological findings (r = ´0.23; p = 0.87). Two of five mares infected with Streptococcus zooepidemicus had a positive cytological result. In contrast, none of the six mares with an Escherichia coli infection showed a positive cytological result. The histological presence of PMN in the stratum compactum of the endometrium is commonly accepted as 'best standard' to diagnose endometritis in mares. Compared to the 'best standard', sensitivity of cytology of CB, US and EB was 0.17, 0.00 and 0.25, respectively. Sensitivity of uterine culture was 0.25, 0.33 and 0.25 for CB, US and EB, respectively.
Cytology in combination with a bacteriological examination of a cytological brush sample resulted in the best sensitivity of 0.42. Based on this result, a combination of a bacteriological and a cytological examination of a cytological brush sample can be recommended as an easy to perform technique to improve the diagnosis of subclinical endometritis in the field compared to the uterine culture as currently used routine method alone.
The objective of the second study was to determine the distribution of PMN within different sampling locations of the equine uterus by cytological and histological examinations and to compare PMN numbers of the two techniques at the corresponding locations. We hypothesized that one sample of either method would represent the actual health status of the whole uterus and that PMN numbers correlate between the methods. Cytological and endometrial biopsy samples were taken in vitro from 37 uteri within 2 ± 1 h after slaughter from five pre-defined locations of each uterus.
Cytological samples were smeared on microscopic slides, stained and classified as negative (< 2% PMN) or positive (≥ 2% PMN) for endometritis.
Histologically, the number of PMN were counted by an experienced pathologist (≥ 5 PMN/3 high power fields in 40 x magnification = positive for endometritis) and grades of endometrosis ('-' to '+++') and angiosclerosis ('-' to '+++') were evaluated. The prevalence of positive cytological and histological samples was 14.6% and 17.8%, respectively. A fair agreement between the two diagnostic methods could be detected (k = 0.29; p < 0.01). A whole uterus was defined as positive for endometritis when at least one of the five sampled locations was scored as positive for the counts of PMN.
A total of 10 and 14 uteri generally positive for endometritis could be detected in cytological and histological examination, respectively. Numbers of PMN differed between the sampling locations resulting in positive and negative locations within the positive uteri, in both, cytological (8/10) and histological examination (13/14).
Nevertheless, significant differences of endometritis positive or negative scores within the different locations could not be detected, neither in cytological (p = 0.56) nor in histological examinations (p = 0.1). Additionally, no significant differences in classification of endometrosis (p = 0.96) and angiosclerosis (p = 0.67) within the locations could be observed.
In conclusion, inflammatory processes are not spread uniformly within the endometrium. Also, the hypothesis that PMN numbers correlate between the two diagnostic methods at a chosen location has to be rejected. Further research is warranted to determine the optimal number of sampling locations in cases of different types of endometritis while maintaining practical feasibility.
Overall, this thesis clearly showed that a single bacteriological or a single cytological examination of the uterus might produce false negative results to identify subclinical endometritis in mares. This might be due to the inhomogenous distribution pattern of PMN within the endometrium. And because of this, the prognostic category according to Kenney and Doig (1986) could also change within one uterus. Therefore, the results of all tested diagnostic techniques should be critically evaluated for the prediction of a mares fertility. The combination of a bacteriological and a cytological examination of the cytological brush is the most easy and promising approach for diagnosing subclinical endometritis in the field. Further research is needed to determine whether the combination of two diagnostic techniques or multiple sampling of the endometrium might improve the reliability of the diagnosis of subclinical endometritis in the mare.