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Arquivo Brasileiro de Medicina Veterinária e Zootecnia

Print version ISSN 0102-0935On-line version ISSN 1678-4162

Arq. Bras. Med. Vet. Zootec. vol.51 no.3 Belo Horizonte June 1999 

Experimental peritonitis in horses: peritoneal fluid composition

(Peritonite experimental em eqüinos: composição do líquido peritoneal)


L.C.N. Mendes1, L.C. Marques2*, G.H. Bechara2, J.R. Peiró1

1Faculdade de Medicina Veterinária da UNESP – Campus Araçatuba
2Faculdade de Ciências Agrárias e Veterinárias da UNESP – Campus Jaboticabal
14870-000 – Jaboticabal, SP


Recebido para publicação em 1 de julho de 1998.
Apoio financeiro da FAPESP.
*Autor para correspondência




Sixteen adult horses were randomly divided into four equal groups of four animals and each group was injected intraperitoneally with one of the following suspension: Group I, 100´107 colony-forming units (CFU) of E. coli diluted in 500ml of 0.9% saline; Group II, 100´107 CFU of Bacteroides fragilis in 500ml of 0.9% saline; Group III, 100´107 CFU of E. coli in combination with 100´107 CFU of B. fragilis in 500ml of 0.9% saline; Group IV, 500ml of 0.9% saline. A significant increase in leukocyte number was observed in the peritoneal fluid by four hours after the inoculations in animals of Group I and II, and by eight hours in animals of Group III. The highest cell count observed was 516´103 leukocytes/mm3. Significant increases in peritoneal fluid fibrinogen (1g/dl) and total protein (9.1%) concentrations were also observed. Horses inoculated with pure cultures of either E. coli or B. fragilis demonstrated mild and self-limiting peritonitis, while those inoculated with a combination of both bacteria demonstrated laboratory findings of higher intensity and duration.

Keywords: Horses, peritonitis, Escherichia coli, Bacteroides fragilis



Dezesseis eqüinos adultos foram aleatoriamente divididos em quatro grupos de quatro animais que receberam inoculação intraperitoneal das seguintes suspenções: grupo I, 100´107 unidades formadoras de colônias (CFU) de E. coli diluídas em 500ml de solução salina a 0,9%; grupo II, 100´107 CFU de Bacteroides fragilis em 500ml de solução salina a 0,9%; grupo III, 100´107 CFU de E. coli combinados com 100´107 CFU de B. fragilis em 500ml de solução salina a 0,9%; grupo IV, 500ml de solução salina a 0,9%. Observou-se aumento significativo do número de leucócitos no líquido peritoneal quatro horas após as inoculações dos animais dos grupos I e II, e oito horas após as inoculações dos animais do grupo III. A contagem mais elevada foi de 516´103 leucócitos/mm3. Aumentos significativos nas concentrações de fibrinogênio (1g/dl) e proteína total (9,1%) foram também observados. Eqüinos inoculados com culturas puras, tanto de E. coli quanto de B. fragilis, apresentaram peritonites mais brandas e autolimitantes, enquanto que eqüinos inoculados com associação das duas bactérias apresentaram alterações laboratoriais com maior intensidade e duração.

Palavras-Chave: Cavalo, peritonite, Escherichia coli, Bacteroides fragilis




Inflammation of the peritoneum, or peritonitis, can occur in response to the presence of a variety of noxious stimuli, including both infectious and noninfectious agents (Trent, 1995). Few studies of natural or experimental peritonitis are avaliable in the literature.

Contamination of the abdomen and injury to the mesothelial cells initiate an inflammatory response and a cascade of events that results in the release of histamine and other vasoactive substances from peritoneal mast cells, vasodilatation and hyperaemia, an increase in peritoneal and vascular permeability, and an influx of protein-rich fluid, macrophages, polymorphonuclear cells, humoral opsonins, natural antibodies and serum complement into the peritoneal cavity (Semrad, 1992).

Escherichia coli and Bacteroides fragilis are bacteria present in the normal intestinal flora of horses and are responsible for natural peritonitis (Ricketts, 1987). Increased mortality in rats submitted to combined E. coli and B. fragilis experimental peritonitis was observed suggesting the occurrence of synergism between these agents (Rotstein & Kao, 1988).

The peritoneal fluid varies in quantity, color (serosanguineous, turbid, floculent, purulent), and character (transudate, exudate, modified transudate or exudate) (Clabough & Ducketts, 1992). In a study of 30 horses with peritonitis, peritoneal fluid of all animals contained increased leukocytes, ranging in number from 11.2´103/mm3 to 385´103/mm3. Most of these cells were neutrophils ranging in frequency from 52% to 99%. Eosinophils were detected in only two horses (Dyson, 1983). Peritoneal protein levels are elevated (Clabough & Duckett, 1992).

Abdominocentesis is an innocuous technique (Schumacher et al., 1985), since only four out of 850 peritoneal fluid analyses presented complications (two cases of abdominal wall cellulitis and two perforations of a distended viscus). Penetration of a healthy nondistended segment of a bowel is inconsequential, as the small hole is quickly sealed over. However, leakage and peritonitis may occur if the viscus is greatly distended and devitalized (Tulleners, 1983).

The evaluation of peritoneal fluid is an important method in the diagnosis of acute abdominal diseases in horses. In this sense, this study was performed to compare the effects of experimental peritonitis on the concentration of total protein, fibrinogen and the cellular composition of the peritoneal fluid.



Sixteen healthy horses (12 male and 4 female) of various breeds, ranging in age from 3 to 10 years, were randomly divided into four groups (GI, GII, GIII and GIV) of four animals each. During the study the horses were housed in individual stalls, fed commercial ration (3kg/animal/day), coast-cross (Cynodon dactilon L) hay and water ad libitum.

Bacteroides fragilis was isolated from a human patient with peritonitis in the Departamento de Microbiologia, Hospital Universitário, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, and was cultivated at the Laboratotório de Anaeróbios, Departamento de Microbiologia, Faculdade de Ciências Agrárias e Veterinárias, UNESP, Campus de Jaboticabal, using Jang & Hirsh (1991) method. Escherichia coli was isolated from a sample of faeces from a healthy horse at the Microbiology Department, at the same university, using Edwards & Ewing (1972) method. The inoculum was standardized as 10´107 colony-forming units (CFU) per millilitre.

For inoculations, paracentesis was performed according to the technique described by White II (1990), and the animals were inoculated intraperitoneally as described in Table 1.



Abdominal fluid was collected into sterilized tubes with EDTA from all animals at 0, 2, 4, 6, 8, 10, 12, 24, 36, 48, 60, 72, 120, 168 and 216 hours after inoculations (HAI) according to the technique described by White II (1990), and physical aspects (colour and turbidity) and laboratorial aspects (total and differential cell counts, total protein and fibrinogen) were determined according to the routine techniques.

Data were submitted to analysis of variance for comparisons between groups at each time, and Tukey test was applied to compare means using the SAS program (Statistical Analysis Systems).



Leukocyte counts in peritoneal fluid were significantly increased in animals of groups I, II and III starting at 4 HAI (Table 2) and polymorphonuclear cells predominated, with a significant increase between 4 and 60 HAI (Table 3). Significantly decreased of mononuclear cells were detected in all horses at 4, 6, 8, 36, 48 and 60 HAI. Eosinophils from group I horses were significantly increased at 4, 6 and 8 HAI.

Total protein in peritoneal fluid was significantly increased from 2 HAI to the end of observation period (Table 4), and fibrinogen was significantly increased from 12 HAI to the end of the observation period (Table 5).



Analysis of peritoneal fluid has been used for the diagnosis and prognosis of abdominal diseases in horses (Tulleners, 1983). The paracentesis technique is safe (White II, 1990) with no complications even after repeated procedures (Tulleners, 1983; Schumacher et al., 1985; Juzwiak et al., 1991). In the present experiment, paracentesis for bacterial inoculation and analysis of peritoneal fluid were successfully performed with fistulations occurring only in group III at the site of inoculation.

A significant increase in peritoneal fluid leukocytes occurred in all experimental groups, with the highest count being 516´103 leukocytes/mm3. Early in the disease process the elevation of white cell count is caused primarily by an increase in polymorphonuclear cells. In chronic cases mononuclear cells and macrophages increase in relation to the polymorphonuclear (Ricketts, 1987; Semrad, 1992; Clabough & Duckett, 1992). In this study it was observed a predominance of polymorphonuclear cells in the peritoneal fluid as also observed in natural peritonitis (Bach & Ricketts, 1974; Dyson, 1983; Moll & Schumacher, 1992). Therefore, our data support those finds reported by other authors, who stated that the analysis of peritoneal fluid was a very important ancillary diagnostic method in abdominal diseases in horses (Bach & Ricketts, 1974; Swanwick & Wilkinson, 1976; Juzwiak et al., 1991).

The increase of total protein in the peritoneal fluid, higher than 2.5g/dl, was a consequence of vascular permeability increase in abdominal viscera (Wilson & Gordon, 1987). Particularly, our data showed a significant elevation in this biochemical component from 2 HAI until the end of the experiment.

Fibrinogen was significantly increased in peritoneal fluid from 12 HAI to the end of the experiment. Fibrinogen values in peritoneal fluid higher than 0.1g/dl indicated vascular damage and/or inflammatory injuries (Wilson & Gordon, 1987). Thus, our data support the idea that the evaluation of this parameter in horses with peritonitis could be an important helping method for diagnosis.

It is concluded that laboratory evaluation of peritoneal fluid reflects the abdominal changes induced by E. coli or B. fragilis similarly to the natural bowel equine disease and predict the systemic alterations that occur during peritonitis.



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