In cattle, PFL is commonly used to correct abomasal disorders or to perform a cesarean section.1 Postoperative complications associated with PFL include peritonitis, adhesions, hemorrhage, and SSI.1,2 The incidence of SSI following laparotomy varies depending on the procedure performed, surgical approach, surgical environment, and intraoperative bacterial contamination.3–5 Most abomasal surgeries are classified as clean procedures with a frequency of SSI < 10 %.6–8 Surgical site infections are classified into 3 categories on the basis of depth, extension of infection, and duration between the procedure and detection of infection.9 A superficial SSI involves the skin and subcutaneous space and becomes detectable within 30 days after the surgical procedure. A deep SSI affects deeper soft tissues, such as muscle and fasciae, and becomes detectable 30 to 90 days after the surgical procedure. An organ and space SSI involves structures deep to muscles and fasciae and becomes detectable 30 to 90 days after the surgical procedure.9,10 An RA is defined as a collection of purulent material between the parietal peritoneum and the abdominal muscle layers (specifically the rectus abdominis or transversus abdominis muscle).1,2,11 Therefore, RAs are classified as deep SSIs. Although the veterinary literature contains anecdotal reports of cattle with RAs,1,2,11 the outcomes for a large number of cattle with RAs have not been formally investigated or reported.
The objective of the study reported here was to describe the history, clinical and clinicopathologic findings, treatments, and outcomes for cattle with RAs. The hypotheses were that surgical drainage of RAs was effective and that affected cattle treated in such a manner would return to satisfactory production levels.
Materials and Methods
Case selection criteria
In March 2017, the medical record database of the veterinary teaching hospital at the University of Montreal was searched to identify cattle that were treated for an RA between January 1995 and March 2017. Keywords used for the search included bovine, abscess, and retroperitoneal.
To be included in the study, each animal had to have an RA > 30 cm in diameter located > 3.5 cm subjacent to the skin as a result of a PFL that was performed < 3 months prior to the initial evaluation for the RA. Diagnosis of an RA was made on the basis of results of a physical examination, abdominal palpation per rectum, and transabdominal ultrasonographic examination. The diameter and extent of the abscess were determined by transabdominal ultrasonography. Cattle with an RA ≤ 30 cm in diameter or that had not undergone a PFL within the 3 months prior to the initial evaluation for the RA were excluded from the study.
Medical records review
For each animal eligible for study inclusion, information extracted from the medical record included age, breed, sex, reason for referral to the veterinary teaching hospital, duration between PFL and initial evaluation for the RA, physical examination and diagnostic test results, surgical procedures performed, treatments administered, duration of antimicrobial administration, duration and cost of hospitalization, and outcome. Most cattle had a CBC and serum biochemical profile performed at hospital admission for the study qualifying event.
Transabdominal ultrasonographic examination
Each animal remained unsedated and underwent a transabdominal ultrasonographic examination of the affected area with a 3.5-MHz curvilinear probe to achieve visualization of deep tissues as described.12–14 Briefly, the affected paralumbar fossa and adjacent flank area were clipped to remove hair and rinsed with warm water. Ultrasound contact gel was applied to the area of interest.15 The upper, middle, and lower thirds of the previous surgical incision were scanned as described16 to confirm the presence of an SSI. Then, the probe was moved to define the depth and diameter of the abscess and its relation to adjacent organs. Peritonitis was ruled out on the basis of visualization of the peritoneal layer without evidence of fluid or fibrin and the presence of free movement of adjacent viscera.12,13 Results of the transabdominal ultrasonographic examination were also used to determine the optimal location for drainage of the RA.
Surgical drainage of RAs
Cattle that underwent surgical drainage of the RA were administered penicillin procainea (21,000 U/kg [9,545 U/lb], IM) and flunixin meglumineb (2.2 mg/kg [1 mg/lb], IV) prior to the procedure. Cattle with extremely large RAs were administered isotonic saline (0.9% NaCl) solution IV during the procedure to prevent hypovolemic shock as the abscess was drained. Surgical drainage of the RA was performed with the animal restrained in a standing position. Analgesia of the drainage area was achieved by a locoregional (ie, modified proximal paravertebral) block or local infiltration with a 2% lidocaine solution. A stab incision was made at the most superficial and ventral aspect of the abscess as determined by the ultrasonographic findings. If there was a draining tract from the previous surgical incision near the ventral aspect of the abscess, an incision was made at the opening of the tract, and the tract was progressively enlarged and extended until the primary pus-filled cavity was breached. Samples of the purulent material drained from the abscess were aseptically collected for aerobic and anaerobic bacterial culture and cytologic evaluation. The abscess was drained slowly to minimize the risk of hypovolemic shock. The incision was extended through the adjacent skin and muscle layers as necessary to facilitate drainage of the abscess. When possible, the incision was extended (generally to a length of approx 15 cm) to allow the surgeon to insert his or her hand and arm into the abscess to facilitate removal of large fibrin clots. Occasionally, transabdominal ultrasonography was used intraoperatively to evaluate the plane of dissection to avoid missing the abscess and entering the abdominal cavity.
Following drainage of the RA, the abscess cavity was lavaged with a diluted (0.1%) povidone-iodine solution (10% povidone-iodine solution with 1% free iodine) as described,17 and a stent bandage was sutured over the incision to prevent environmental contamination. The abscess cavity was lavaged as previously described, and the stent bandage was changed on a daily basis until a hand could no longer be inserted into the cavity, it was no longer actively draining purulent material, and it was covered with a healthy layer of granulation tissue.
Outcomes
Short-term outcome was defined as the status (alive or dead) of the animal at hospital discharge. Because all study animals were adult dairy cattle, long-term outcome was determined by analysis of the milk production data for each cow for at least 6 months after hospital discharge. Production data were obtained from the Canadian Dairy Network database.
Statistical analysis
All data were recorded in a computerized spreadsheet program,c and descriptive statistics were generated by use of statistical functions available through that program.
To evaluate the hypothesis that cattle with RAs that underwent surgical drainage of the abscess would return to satisfactory production levels, milk production data for each cow were obtained for 3 lactations (the lactations before, during, and after the cow developed the RA) whenever possible. For each cow and lactation, milk production was standardized to a lactation that was 305 days in length. Standardized milk production was calculated by the Canadian Dairy Network on the basis of available milk production data for each cow and use of validated equations that take into account multiple factors such as the cow's breed and age and the number of days since parturition. Two-sided paired t tests were used to compare milk production between the lactations before (preabscess lactation) and during which (abscess lactation) the cow developed an RA and between the abscess lactation and subsequent lactation (postabscess lactation). Values of P ≤ 0.05 were considered significant, and t tests were performed with a commercially available statistical software program.d
Results
Cows
The medical records search yielded records for 54 cows. Twenty-two cows were excluded from the study because the RA was < 30 cm in diameter or < 3.5 cm subjacent to the skin or because the cow did not have a history of PFL within the 3 months prior to evaluation for the RA. The remaining 32 cows met the inclusion criteria and were evaluated in the study.
All study animals were adult Holstein cows with a mean ± SD age of 4.1 ± 1.3 years (median, 3.2 years; range, 2.2 to 7.0 years). Reasons provided for referral to the veterinary hospital included anorexia (n = 10 cows), postoperative complications related to the surgical incision (7), fever (5), decreased milk production with or without fever and anorexia (4), digestive abnormalities (2), and peritonitis (2); the reason for referral was not specified for 2 cows.
Thirty of the 32 (94%) cows underwent a right PFL prior to the initial evaluation for the RA at the veterinary teaching hospital. Procedures performed for those cows included omentopexy for (n = 16) or unspecified correction of (12) an abomasal displacement, unspecified cecal surgery (1), and exploratory laparotomy (1). For the 28 cows that underwent surgical correction of an abomasal displacement, the type of displacement (left, right, or volvulus) was not specified in the records. The remaining 2 cows underwent a left PFL to perform a rumenotomy and cesarean section for removal of a dead calf.
The interval between PFL and hospital admission for the RA was documented for 26 cows. The mean ± SD duration between PFL and hospital admission was 31 ± 14.4 days (median, 26 days; range, 9 to 71 days).
Information regarding on-farm antimicrobial administration was available for 16 of the 32 (50%) cows. The mean duration of on-farm antimicrobial administration was 4 days (median, 2 days; range, 1 to 10 days). Antimicrobials administered on farm included a combination of trimethoprim-sulfadoxinee,f and penicillin procainea (n = 7), penicillin procainea (4), ceftiofur hydrochlorideg (2), a combination of trimethoprim-sulfadoxinee and oxytetracyclineh (2), and ampicillini (1). All antimicrobials were administered in accordance with Canadian regulations regarding extralabel drug use in food producing animals.
Clinical signs and physical examination findings
The mean ± SD rectal temperature was 38.7° ± 8.5°C (101.7° ± 15.3°F; median, 38.8°C [101.8°F]; range, 37.3°C to 39.8°C [99.1°F to 103.6°F]). Ten of the 32 (31%) cows were febrile (rectal temperature > 39.2°C [102.6°F]) during the initial physical examination at the teaching hospital.
The mean ± SD HR was 82 ± 5 beats/min (median, 80 beats/min; range, 57 to 140 beats/min). Eight cows were tachycardic (HR > 80 beats/min) and 1 cow was bradycardic (HR < 60 beats/min) during the initial physical examination.
The RR during the initial physical examination was recorded for 30 of the 32 cows. The mean ± SD RR for those cows was 29 ± 7 breaths/min (median, 27 breaths/min; range, 18 to 52 breaths/min). Nine and 6 cows had tachypnea (RR > 40 breaths/min) and bradypnea (RR < 24 breaths/min), respectively.
Hydration status was considered clinically normal for 20 of the 32 (63%) cows. Nine cows were estimated to be between 5% and 7% dehydrated, and 2 cows were estimated to be between 8% and 19% dehydrated. One cow was noted as dehydrated, but the estimated extent of dehydration was not recorded in the record.
Rumen motility was recorded for 29 of the 32 (91%) cows. Clinically normal rumen motility was defined as 3 complete rumen contractions/2 min. Rumen motility was considered clinically normal for 5 cows, hypomotile for 22 cows, and hypermotile for 2 cows. Fecal consistency was reported for all 32 cows. Feces were described as clinically normal for 18 cows. Nine cows were described has having diarrhea. Two cows had fecal material that contained a large proportion of undigested grain or long forage particles (particle size > 1.3 cm [0.5 inches]). Feces were described as having a paste-like consistency for 2 cows and as abnormally dry for 1 cow.
Information regarding abdominal palpation per rectum was available for 30 cows. Results were strongly suggestive of an RA for 25 (83%) of those cows. In most instances, the RA was described as a large firm mass with a smooth surface that protruded into the abdominal cavity in the region of the previous PFL.
Clinicopathologic findings
A CBC and serum biochemical profile were performed at the time of hospital admission for 31 of the 32 (97%) cows (Table 1). The Hct and RBC count were below the lower limit of the respective reference ranges for 16 (52%) and 30 (97%) cows, respectively. Twenty-seven (87%) cows were neutrophilic, and 19 (61%) cows were hyperfibrinogenemic.
Summary of hematologic and serum biochemical profile results at hospital admission for 31 of 32 adult Holstein cows that underwent surgical drainage of an RA at a veterinary teaching hospital between January 1995 and March 2017.
| Variable | Reference range | Mean ± SD | Median (range) |
|---|---|---|---|
| Hct (%) | 26–49 | 0.25 ± 0.07 | 0.25 (0.18–0.38) |
| Hemoglobin (g/L) | 98.00–153.00 | 91.6 ± 9.9 | 89 (67–136) |
| RBC (× 1012 cells/L) | 7.40–11.60 | 5.60 ± 0.60 | 5.60 (3.93–7.62) |
| WBC (× 109 cells/L) | 6.20–13.60 | 10.40 ± 3.60 | 8.4 (4.2–25.5) |
| Neutrophils (× 109 cells/L) | 1.10–3.60 | 7.2 ± 3.0 | 6.2 (2–20) |
| Nonsegmented neutrophils (× 109 cells/L) | 0–0.19 | 0.03 ± 0.05 | 0 (0–0.04) |
| Fibrinogen (g/L) | 2–4 | 6 ± 1.5 | 6 (2–10) |
| Lymphocytes (× 109 cells/L) | 4.00–10.00 | 2.6 ± 0.8 | 2.4 (0.98–6.89) |
| Glucose (mmol/L) | 2.6–4.9 | 4.3 ± 0.8 | 4.3 (2–7.5) |
| Urea (mmol/L) | 1.61–6.51 | 3.5 ± 1.27 | 3 (1.6–12.7) |
| Creatinine (mmol/L) | 38–116 | 70 ± 17.0 | 66 (31–183) |
| Total bilirubin (mmol/L) | 0–14.0 | 11 ± 4.0 | 9.6 (3–25) |
| Aspartate aminotransferase (U/L) | 30–104 | 91 ± 31.0 | 85 (37–249) |
| γ-Glutamyltransferase (U/L) | 10–39 | 48.5 ± 23.7 | 40 (15–127) |
| Total proteins (g/L) | 59.5–80.0 | 65.4 ± 6.0 | 68 (53–80) |
| Albumin (g/L) | 27.7–40.4 | 22 ± 4.5 | 22 (14–34) |
| Globulin (g/L) | 26.2–45.2 | 43 ± 5.3 | 44 (35–59) |
| Albumin-to-globulin ratio | 0.61–1.33 | 0.53 ± 0.13 | 0.5 (0.25–0.85) |
| Calcium (mmol/L) | 2.22–2.70 | 2.06 ± 0.13 | 2 (1.81–2.55) |
| Potassium (mmol/L) | 3.86–5.28 | 4 ± 0.45 | 4 (2–5.3) |
| Sodium (mmol/L) | 134.0–147.0 | 138 ± 2.7 | 137 (127–143) |
| Chloride (mmol/L) | 96.4–109.2 | 98 ± 3.6 | 98 (87–112) |
| Tco2 (mmol/L) | 22–33 | 30 ± 2.2 | 30 (22–34) |
| β-Hydroxybutyrate (mmol/L) | 324–1,296 | 384 ± 150 | 300 (142–720) |
To be included in the study, each cow had to have an RA > 30 cm in diameter located > 3.5 cm subjacent to the skin as a result of a PFL that was performed < 3 months prior to the initial evaluation for the RA.
Tco2 = Total concentration of carbon dioxide.
The total serum protein concentration was within the reference range for all 31 cows for which it was evaluated. Twelve (39%) cows were hyperglobulinemic, and 26 (84%) cows were hypoalbuminemic. Twenty-five (81%) cows were hypocalcemic. Thirteen (42%) cows were hypokalemic, and 8 (26%) were hyperglycemic.
Transabdominal ultrasonographic findings
For all 32 cows, transabdominal ultrasonographic examination revealed the presence of a large amount of heteroechoic material inside a mostly anechoic cavity, which was compatible with an abscess (Figure 1). The abscess was confirmed to be in close proximity to the previous surgical incision for 6 of the 32 (19%) cows. Because the ultrasound probe used could only penetrate the tissue to a depth of 35 cm, the exact diameter of the abscess could not be precisely measured for most cows. The extension of the RA in the paralumbar fossa varied among the cows but was consistently wide for all cows. In some cows, the cranial margin of the abscess extended to the diaphragmatic surface of the liver and the caudal margin of the abscess extended to the tuber coxae region.
Representative transabdominal ultrasonographic image of an RA in the paralumbar fossa of an adult Holstein cow. The image was acquired with a 3.5-MHz curvilinear probe that was capable of penetrating tissues to a depth of 35 cm. In this image, the skin (asterisk), fibrin associated with the abscess capsule (dagger), heteroechoic purulent material (double dagger), peritoneum (section mark), and portions of the gastrointestinal tract (parallel marks) are visible. Scale in centimeters appears on the right side of the image.
Citation: Journal of the American Veterinary Medical Association 256, 7; 10.2460/javma.256.7.814
Representative transabdominal ultrasonographic image of an RA in the paralumbar fossa of an adult Holstein cow. The image was acquired with a 3.5-MHz curvilinear probe that was capable of penetrating tissues to a depth of 35 cm. In this image, the skin (asterisk), fibrin associated with the abscess capsule (dagger), heteroechoic purulent material (double dagger), peritoneum (section mark), and portions of the gastrointestinal tract (parallel marks) are visible. Scale in centimeters appears on the right side of the image.
Citation: Journal of the American Veterinary Medical Association 256, 7; 10.2460/javma.256.7.814
Representative transabdominal ultrasonographic image of an RA in the paralumbar fossa of an adult Holstein cow. The image was acquired with a 3.5-MHz curvilinear probe that was capable of penetrating tissues to a depth of 35 cm. In this image, the skin (asterisk), fibrin associated with the abscess capsule (dagger), heteroechoic purulent material (double dagger), peritoneum (section mark), and portions of the gastrointestinal tract (parallel marks) are visible. Scale in centimeters appears on the right side of the image.
Citation: Journal of the American Veterinary Medical Association 256, 7; 10.2460/javma.256.7.814
Bacteriologic and cytologic findings
Bacteriologic culture results for abscess contents were available for 26 of the 32 (81%) cows. Trueperella pyogenes was isolated in pure culture for 8 (31%) cows. A mixed flora of T pyogenes, Bacteroides stercoris, Peptostreptococcus spp, coliform spp, and Enterococcus spp was cultured for 6 (23%) cows. Escherichia coli was isolated in pure culture for 2 (8%) cows. Pure cultures of Pseudomonas aeruginosa, a Prevotella sp, and Enterococcus faecium were isolated from 1 cow each. Bacteriologic culture of abscess contents yielded no growth for 7 cows.
Cytologic evaluation of the purulent material drained from the RA was performed for 14 cows. For those 14 samples, the mean ± SD percentage of neutrophils was 89.5 ± 7.5% (median, 93%; range, 60% to 100%), lymphocytes was 2.75 ± 0.87% (median, 3%; range, 1% to 4%), and macrophages was 15 ± 8.9% (median, 6%; range, 1% to 40%).
Treatment
Twenty-nine of the 32 (91%) cows underwent surgical drainage of the RA. One cow had a functional draining tract from the previous surgical incision that was considered adequate for drainage of the RA. The owners of 2 cows declined surgical drainage of the RA owing to concomitant peritonitis and financial constraints. For the RAs that underwent surgical drainage, the volume of material removed from the abscess cavity was estimated to range between 10 and 40 L. Fibrinous material was manually removed from the abscess cavity when present (Figure 2). A stent bandage was sutured in place and changed daily to prevent contamination of the abscess cavity with bedding, feces, and flies.
Representative photograph of the right paralumbar fossa and flank region of an adult Holstein cow that was examined because of chronic fever following a PFL to perform an omentopexy for correction of an abomasal displacement. The cow had a large (> 30 cm in diameter) RA that was associated with the previous surgical incision. The abscess was surgically drained. This photograph shows a large fibrin clot that is in the process of being manually removed from the abscess cavity.
Citation: Journal of the American Veterinary Medical Association 256, 7; 10.2460/javma.256.7.814
Representative photograph of the right paralumbar fossa and flank region of an adult Holstein cow that was examined because of chronic fever following a PFL to perform an omentopexy for correction of an abomasal displacement. The cow had a large (> 30 cm in diameter) RA that was associated with the previous surgical incision. The abscess was surgically drained. This photograph shows a large fibrin clot that is in the process of being manually removed from the abscess cavity.
Citation: Journal of the American Veterinary Medical Association 256, 7; 10.2460/javma.256.7.814
Representative photograph of the right paralumbar fossa and flank region of an adult Holstein cow that was examined because of chronic fever following a PFL to perform an omentopexy for correction of an abomasal displacement. The cow had a large (> 30 cm in diameter) RA that was associated with the previous surgical incision. The abscess was surgically drained. This photograph shows a large fibrin clot that is in the process of being manually removed from the abscess cavity.
Citation: Journal of the American Veterinary Medical Association 256, 7; 10.2460/javma.256.7.814
For the 30 cows that underwent drainage of the RA, the evacuated abscess cavity was lavaged with 10 L of lukewarm tap water containing approximately 100 mL of 10% povidone-iodine solution on a daily basis for a mean of 11 days (median, 10 days; range, 0 to 32 days; Figure 3). For 8 cows, the abscess cavity was filled with 1 kg of white granulated sugar following each daily lavage to improve healing, stimulate granulation tissue growth, and control infection.
Close-up photograph of the incision in the right paralumbar fossa of the cow of Figure 2 that was obtained 1 week after surgical drainage and initiation of daily localized treatment of the RA. The incision through the abdominal skin and musculature is covered with healthy-appearing granulation tissue, and fibrin coats the inside of the abscess capsule. The depth of the abscess can also be appreciated.
Citation: Journal of the American Veterinary Medical Association 256, 7; 10.2460/javma.256.7.814
Close-up photograph of the incision in the right paralumbar fossa of the cow of Figure 2 that was obtained 1 week after surgical drainage and initiation of daily localized treatment of the RA. The incision through the abdominal skin and musculature is covered with healthy-appearing granulation tissue, and fibrin coats the inside of the abscess capsule. The depth of the abscess can also be appreciated.
Citation: Journal of the American Veterinary Medical Association 256, 7; 10.2460/javma.256.7.814
Close-up photograph of the incision in the right paralumbar fossa of the cow of Figure 2 that was obtained 1 week after surgical drainage and initiation of daily localized treatment of the RA. The incision through the abdominal skin and musculature is covered with healthy-appearing granulation tissue, and fibrin coats the inside of the abscess capsule. The depth of the abscess can also be appreciated.
Citation: Journal of the American Veterinary Medical Association 256, 7; 10.2460/javma.256.7.814
Twenty-three of the 30 (77%) treated cows were administered IV fluids to prevent hypovolemic shock during surgical drainage of the RA. All 30 cows received antimicrobials during the perioperative period. Antimicrobials were administered daily after surgery until the cow was discharged from the hospital or in accordance with the attending clinician's preference. The mean duration of antimicrobial treatment was 17 days (median, 16 days; range, 1 to 42 days). The antimicrobial treatment regimens most frequently administered were sodium ampicillin (10 mg/kg [4.5 mg/lb], IV, q 8 h), ceftiofur sodium (2.2 mg/kg, IV, q 24 h), penicillin procaine (21,000 U/kg, IM, q 12 h), trimethoprim-sulfadoxine (16 mg/kg [7.3 mg/lb], IV, q 12 h), and oxytetracycline (10 mg/kg, IV, q 12 h).
The mean ± SD duration of hospitalization was 14 ± 8 days (median, 19 days; range, 1 to 46 days). The mean ± SD cost of hospitalization was CaD$1,466 ± 290 (median, CaD$1,162; range, CaD$320 to CaD$3,804)
Outcome
Thirty of the 32 (94%) cows were discharged from the hospital alive. Two cows were euthanized because the infection had spread to the peritoneal cavity; for 1 of those cows, peritonitis developed after the RA was drained. For both euthanized cows, communication between the RA and peritoneal cavity was discovered during necropsy.
For the cows that were discharged alive, owners were instructed to clean the incision on a daily basis. One cow was discharged from the hospital after only a few days owing to financial constraints, and the owner continued to lavage the abscess cavity on the farm by use of a stomach tube and pump. All owners were instructed to discard the milk of treated cows until it tested free of antimicrobial residues because most cows were administered antimicrobials for a longer duration than indicated on the label instructions (ie, in an extralabel manner), which negated the labeled withdrawal time. The attending clinician for each treated cow contacted the referring veterinarian and requested that the cow be reexamined 10 to 14 days after discharge from the teaching hospital.
Long-term milk production data were available for 14 of the 30 (47%) cows that survived to hospital discharge. Twelve cows completed the abscess lactation (lactation during which the RA developed), and the mean standardized milk production for the abscess lactation was 9,147 kg. Seven cows completed the lactation subsequent to the abscess lactation (postabscess lactation), and the mean standardized milk production for the postabscess lactation was 11,515 kg. One cow completed 4 lactations, and another cow completed 6 lactations after the abscess lactation. Standardized milk production did not differ significantly between the abscess lactation and the preabscess lactation (lactation immediately before the abscess lactation; P = 0.17) or postabscess lactation (P = 0.23).
Discussion
Retroperitoneal abscesses have been described in multiple species.18–22 In human patients, an RA usually originates from a systemic infection rather than from an SSI.23–25 In dogs, RAs have been reported subsequent to ovariohysterectomy or grass awn migration.21,22 In cattle, RAs are an infrequent complication associated with PFL. Surgical correction of abomasal displacement and cesarean section are 2 of the most commonly performed surgeries in cattle5 and are commonly performed via a PFL approach. Although SSI has been reported as a complication following omentopexy7,8,26,27 and cesarean section28–30 in cattle, RA is generally not listed as a potential complication for those surgeries.26–30 That is probably because RAs in cattle are typically not detected until weeks to months after PFL, and the clinical signs manifested are often not obviously related to the previous surgery. Anorexia can be caused by the presence of circulating cytokines from the inflammatory process or by pain secondary to retroperitoneal dissection of the abscess.11 Progressive accumulation of purulent material along the abdominal wall will also eventually cause signs of discomfort and anorexia.2,11
In dogs and human patients with RAs, the most common clinical manifestations are fever and signs of pain.21–23 For the cows with RAs evaluated in the present study, the most frequently recorded clinical sign was rumen hypomotility, which might have been a consequence of pain (ie, an increase in sympathetic tone and adrenal secretory activity) as well as systemic inflammation and anorexia.11,31,32 The second most frequently recorded clinical sign for the cows of this study was tachycardia, which might have also been a consequence of pain.
In the present study, the RA could be palpated per rectum for 25 of the 30 (83%) cows that underwent abdominal palpation per rectum. For some of those cows, it was difficult to evaluate the extent of the abscess owing to its size and location, the presence of the rumen, and the ability of the palpator (who may have been limited in terms of arm length or experience). Nonetheless, abdominal palpation per rectum should be part of the physical examination of any cow that is suspected of having an RA, especially when ultrasonography is not readily available.
For all 32 cows of the present study, the diagnosis of RA was confirmed on the basis of results of a transabdominal ultrasonographic examination. Although a low-frequency curvilinear probe was used to ultrasonographically examine the cows of this study, we believe that a linear rectal ultrasound probe can be used to successfully identify an RA and determine its margins. Ultrasonographic findings can also be used to determine the optimal location for surgical drainage of an RA. Most large animal ambulatory veterinarians have access to a portable ultrasound unit equipped with a linear rectal probe, which should facilitate diagnosis of RAs on farm.
The hematologic and serum biochemical findings for the cows of the present study were compatible with a chronic inflammatory process. The abnormally low Hct and RBC count were likely secondary to chronic inflammation.33 The pathological mechanism that leads to a decrease in the Hct and RBC count is multifactorial and results from an increase in concentrations of soluble inflammatory mediators that shorten the life span of RBCs and impair bone marrow production of RBCs.33 Neutrophilia with or without leukocytosis, hyperfibrinogenemia, and hyperglobulinemia is also suggestive of a chronic active inflammatory process.11,33 The serum total protein concentration was within the reference range for all cows evaluated in the present study, most likely because hyperglobulinemia was concomitant with hypoalbuminemia or the globulin concentration was within the reference range.11,34 Hypoalbuminemia was likely the result of the combined effects of inflammation and a catabolic state and inadequate protein and caloric intake in patients with a chronic disease process.35
In many species, culture of purulent material from RAs often results in polymicrobial growth.18,23,36,37 For human patients, Staphylococcus aureus is the most common bacterium isolated from RAs that originate from pancreatic36,37 or skin infections.21 For dogs, Proteus mirabilis and E coli are the bacteria most frequently isolated from RAs secondary to urogenital infections,21 and abscesses secondary to skin or oral cavity infections often yield polymicrobial bacterial cultures.22
For livestock that undergo surgical procedures on farm, contamination of the surgical site from the environment is the likely cause of most SSIs. For cattle, there are 3 important bacterial culture patterns that provide hints to the possible route of contamination. Trueperella pyogenes is a commensal pathogen of cattle that causes various suppurative infections and is considered a normal habitant of the skin, mucosal membranes, and rumen.38 Clinical samples from cattle that yield a pure culture of T pyogenes generally represent autogenous infections that originated from the skin or a mucosal membrane, although contamination via flies in the environment cannot be ruled out.39 Samples that yield polymicrobial growth on culture likely originated from infections that resulted from environmental contamination of the surgical site or surgical instruments. Samples that yield a pure culture of E coli could have originated from infections subsequent to inadvertent perforation of the digestive tract during the surgical procedure (eg, rumenotomy).
Treatment of RAs should consist of surgical drainage of the abscess and systemic administration of antimicrobials.1,2,11,18,21,22 Although lancing an abscess may seem like a routine procedure, lancing an RA should be performed with care to avoid leakage of purulent material into the abdomen. The incision site for RA drainage is best determined by ultrasonographic findings or the location of a draining tract. Ideally, the incision is located at the most superficial and ventral aspects of the abscess. A fistulous tract associated with a previous surgical incision can be used as a starting point for abscess drainage; however, the fistulous tract may not be the optimal drainage point depending on the size and relation of the abscess to the tract. Moreover, not all cattle with RAs have draining tracts. Also, the previous surgical incision site might be substantially thicker and more fibrotic than normal, which will make accessing the abscess difficult. Therefore, drainage of the abscess from a point adjacent to the previous surgical incision may be easier.
For patients with large RAs, surgical drainage of the purulent material should be performed in a controlled manner to prevent hypovolemic shock. Rapid decompression of a space occupying lesion such as a large abscess can change the pressure within the abdomen, leading to an abrupt decrease in cardiac preload and shock.40
All cattle evaluated in the present study were adult dairy cows, and the majority (30/32 [94%]) had undergone a right PFL prior to treatment for the RA, most for an omentopexy (n = 16) or some other unspecified procedure (12) for correction of an abomasal displacement. Although the study population reflected the cattle population (ie, mostly dairy cattle) examined and treated at our hospital, the results may not be applicable to other cattle populations.
For cattle with RAs, the large size of the abscess generally requires prolonged treatment and hospitalization, compared with routine abdominal surgeries. Daily treatment of abscesses can be difficult to manage in a farm environment, but treatment in a hospital setting can become costly. In fact, the owners of 2 cows evaluated in the present study declined treatment, in part, because of financial constraints.
For 8 of the 32 (25%) cows evaluated in the present study, the abscess cavity was filled with white granulated sugar following daily lavage to control infection and stimulate the generation of granulation tissue.41,42 Sugar facilitates the formation of granulation tissue owing to its angiogenetic properties, ability to stimulate cell-induced debridement of necrotic tissue, and high osmolality, which inhibits bacterial overgrowth.41,42 Daily lavage of the abscess cavity prevented premature closure of the drainage incision and abscess recurrence. It also allowed for removal of large fibrin clots. The stent bandage was loosely applied to the incision; thus, it did not prevent drainage but did prevent gross contamination of the incision by bedding (eg, straw) and flies.
Limitations of the present study were typical of those for any retrospective study. Specifically, the results were dependent on the thoroughness and completeness of the medical records. The inclusion of only cattle with an RA > 30 cm in diameter and located > 3.5 cm subjacent to the skin could also be viewed as a limitation. We chose those criteria regarding abscess size and location because we wanted to avoid any possible confusion between a superficial SSI and RA. We also believed that smaller abscesses were unlikely to cause clinical signs of sufficient severity to warrant notice. Because drainage of an RA from the primary surgical site, when present, is often unsubstantial, we believe that RA is likely underdiagnosed in cattle. A retrospective study that included all cattle with an SSI would have yielded more comprehensive information regarding cows with RAs across the full spectrum of possible abscess sizes and locations rather than just the most severely affected cows, as did the present study.
Results of the present study indicated that RA is an uncommon complication associated with PFL in cattle (ie, only 32 cows over a 22-year period met the study inclusion criteria). The cows with RAs evaluated in this study generally had nonspecific clinical signs (eg, rumen hypomotility, anorexia, and fever) and a recent history of a PFL. Diagnosis of RA was confirmed by findings of a physical examination, abdominal palpation per rectum, and transabdominal ultrasonographic examination. Most cows were successfully treated by surgical drainage of the abscess and administration of systemic antimicrobials. However, treatment generally required weeks and could be costly. Nevertheless, most cows with RAs returned to their previous level of milk production following treatment.
ABBREVIATIONS
| HR | Heart rate |
| PFL | Paralumbar fossa laparotomy |
| RA | Retroperitoneal abscess |
| RR | Respiratory rate |
| SSI | Surgical site infection |
Footnotes
Depocillin, Intervet Canada Corp, Merck Animal Health, Kirkland, QC, Canada.
Banamine, Merck Animal Health, Madison, NJ.
Excel, Microsoft Corp, Redmond, Wash.
SAS, version 9.4, SAS Institute Inc, Cary, NC.
Borgal, Intervet Canada Corp, Merck Animal Health, Kirkland, QC, Canada.
Trimidox, Vetoquinol N-A Inc, Lavaltrie, QC, Canada.
Excenel RTU EZ, Zoetis Canada Inc, Kirkland, QC, Canada. h. Oxyvet 100 LP, Vetoquinol N-A Inc, Lavaltrie, QC, Canada.
Polyflex, Boehringer Ingelheim Ltd, Burlington, ON, Canada.
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