Validation of three diagnostic techniques to diagnose subclinical endometritis in mares

Endometritis in the mare still constitutes a great problem in the management of broodmares (Bain, 1966; Causey, 2006; LeBlanc and Causey, 2009). It is ranked as the third most common clinical condition in horses (Traub-Dargatz et al., 1991). Such inflammatory conditions of the equine uterus can be classified as acute, chronic or subclinical endometritis (LeBlanc and Causey, 2009; Hurtgen, 2006). All forms of endomeritis may cause substantial reductions of a mare’s fertility. Therefore, endometritis has developed as one of the major problems in the horse breeding industry (Hurtgen, 2006; Liu and Troedsson, 2008). During the breeding season, a timely diagnosis and an efficient treatment is essential for a successful breeding outcome (LeBlanc, 2010; Witte et al., 2010). Prebreeding diagnosis of endometritis should include clinical examination, transrectal palpation, ultrasonography of the reproductive tract, vaginal examination, uterine culture, cytology and endometrial biopsy (Couto and Hughes, 1984; Reiswig et al., 1993; Bourke et al., 1997; Dascanio et al., 1997; Card, 2005; Aguilar et al., 2006). Although there is a wide spectrum of diagnostic aids, identifying the reason for infertility still challenges practitioners in the field. Uterine cultures have been known to lead to false positive and false negative results (Waelchli et al., 1988; Pycock and Newcombe, 1997; Nielsen, 2005; Aguilar, 2006). Therefore, they have been regarded as poor predictors of fertility (Digby and Ricketts, 1982; Shideler et al., 1982). While taking a single sample, the uterine swab touches only a small area of the endometrium and thus, focal infections may be missed (Brook, 1984; Ball et al., 1988). For practical reasons, endometrial culture, however, is still the most common method for diagnosing infectious endometritis in mares in the field (Blanchard et al., 1981; Mackintosh, 1981; Dascanio et al., 1997; Card, 2005). In the last several years it has been repeatedly demonstrated that uterine cytology diagnoses significantly higher percentages of mares with endometritis compared to uterine culture (Ball et al., 1988; Nielsen, 2005; Riddle et al., 2007). Nevertheless, these studies also showed that the cytological examination is still not able to reach the accuracy of the histological examination commonly known as the 'best standard' method (Reiswig et al., 1993; Bourke et al., 1997; Nielsen, 2005; LeBlanc et al., 2007). Therefore it has been recommended to combine a bacteriological with either a cytological or histological examination to get a more reliable diagnosis of inflammatory processes (Digby and Ricketts, 1982). Additionally, in recent years the problem of subclinical inflammatory processes became more obvious. Subclinical endometritis has currently been described as an endometritis with absent clinical signs, such as intrauterine fluid accumulation in ultrasonography (LeBlanc and Causey, 2009). Concerning subclinical endometritis, ultrasonography and uterine culture may cause false negative examination results (LeBlanc and Causey, 2009). In contrast, the exsudative types of endometritis, which show fluid accumulation within the uterus, are more easy to detect with the currently used diagnostic methods (Reiswig et al., 1993; Bourke et al., 1997; Dascanio et al., 1997; Card, 2005; LeBlanc and Causey, 2009). Thus, recently it has become more and more obvious that identifying the cause for sub- or infertility might require more than swabbing (LeBlanc, 2010).