Surgery of the Neonatal Bovine Digestive Tract

Surgery of the Neonatal Bovine Digestive Tract

Surgery of the Bovine Digestive Tract 0749-0720/90 $0.00 + .20 Surgery of the Neonatal Bovine Digestive Tract David C. Bristol, DVM, * and Susan L...

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Surgery of the Bovine Digestive Tract

0749-0720/90 $0.00

+ .20

Surgery of the Neonatal Bovine Digestive Tract

David C. Bristol, DVM, * and Susan L. Fubini, DVMt

Digestive system problems requiring surgical intervention are relatively infrequent in calves, but when they occur, they need to be recognized and treated promptly if a successful outcome is to be obtained. Some problems are observed only in neonates, such as atresia coli; others are seen both in neonates and adults. Diseases common to calves and adults may have different etiologies in the different age groups and may require different treatments. This article will address disorders of the calf's digestive system amenable to surgical therapy and prone to associated complications. The signalment of calves with digestive disease can give important clues as to the cause of the current problem. Several congenital abnormalities have been described to occur in specific breeds (Table 1). Within breeds, certain bloodlines have been associated with digestive abnormalities. The age of the calf is also important when considering digestive abnormalities. Many disorders are associated with different ages of onset. Atresia of segments of the intestinal tract or the anus is usually recognized in the first week of life. 43 Abomasal ulcers are frequently observed in young calves, with an increasing incidence from 4 to 14 weeks of age. 53 Abomasal volvulus and intestinal accidents are usually seen in older calves, but have also been seen in neonates. 39,61 *Diplomate, American Board of Veterinary Practitioners; Assistant Professor, Surgery, North Carolina State University College of Veterinary Medicine, Raleigh, North Carolina tDiplomate, American College of Veterinary Surgeons; Assistant Professor of Surgery, Department of Clinical Sciences, New York State College of Veterinary Medicine, Cornell University, Ithaca, New York Veterinary Clinics o/North America: Food Animal Practice-Vol. 6, No.2, July 1990

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Table 1. Congenital Disorders of the Bovine Digestive System BREED

ABNORMALITY

Many

Cleft palate

Charolais Dutch Friesian Brown Swiss

Cleft palate & arthrogryposis Smooth tongue Smooth tongue

Swedish Highland Jersey Many Many

Atresia ilei Rectovaginal constriction Atresia coli Atresia ani

Jersey

Atresia jejuni

ETIOLOGY

REFERENCE

Chromosomal abnormalities Autosomal recessive?

8

Possibly recessive Incompletely penetrant dominant Autosomal recessive Autosomal recessive Palpation trauma Autosomal recessive? Inherited? Autosomal recessive?

34,35 34,35

2

47 35 42,44 54 2 2

EXAMINATION OF CALVES WITH SUSPECTED GASTROINTESTINAL DISEASE The cardiovascular status of calves with suspected gastrointestinal disorders should be established early in the course of the physical examination. Many of the disorders result in rapid dehydration, which may lead to hypovolemic shock. Shock may also occur from the release of endotoxins from devitalized bowel. Almost without exception, rehydration of animals with suspected gastrointestinal obstruction should be by the intravenous route. The heart and respiratory rates can be used as general indicators of the animal's acid-base status, as acidosis will result in increases in both rates. Because of low reserves of energy, calves with gastrointestinal disease may rapidly become hypoglycemic. Intravenous dextrose therapy is often an essential part of the preoperative therapy. Palpation of the abdomen is combined with inspection of the abdominal contour to aid in determining the type of disorder present. Distention of the rumen is fairly obvious on the left side of the abdomen. This must be differentiated from left displacement of the abomasum. Right-sided abdominal distention occurs with abomasal volvulus or obstruction of the intestinal tract. Palpation of the abdomen of a standing calf or one in left lateral recumbency is useful in assessing intestinal involvement, as distended small or large intestine is usually easily palpable in a young animal. While examining the abdomen, it is important to realize the relative size of the rumen and abomasum are much different in calves than adults. The ratio of the rumen to abomasum in neonates is approximately 1: 2.7, but by 8 weeks of age the two organs are similar in size, and in adult cows the ratio is approximately 9 : 1.46 The development of the rumen depends on the type and amount of feed ingested. 31 In addition to the routine physical and laboratory examinations, it is extremely important to determine that adequate circulating antibody

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levels are present. "Adequate" ingestion of colostrum, even if administered by stomach tube, cannot be equated with adequate absorption, particularly in neonates with gastrointestinal obstruction. The peritoneal fluid should also be examined. Serosanguinous fluid is characteristic of devitalized bowel and is an indication for immediate surgical intervention. SPECIFIC DISORDERS OF THE NEONATE DIGESTIVE TRACT ESOPHAGEAL DISORDERS

Fortunately, esophageal problems are rare in calves. Megaesophagus has been reported in a calf that regurgitated 3 to 9 minutes after ingesting hay, but treatment was not pursued. 65 Lacerations of the esophagus may occur after ingestion of sharp objects, or may occur iatrogenically when wires are used to remove foreign bodies. 68 These may result in abscesses with secondary respiratory embarrassment. Treatment is by drainage, and institution of antibiotic therapy is based on culture and sensitivity testing. Complications of esophageallacerations include cellulitis, compression of adjacent structures by abscess formation, pleuritis, and mediastinitis. 68 DISORDERS OF THE FORESTOMACH

Recurrent bloat (Fig. 1) is a fairly common problem in calves, and many etiologies have been proposed. These include poor development of the belching mechanism, compression or inflammation of the vagal nerves secondary to intrathoracic disease, obstruction of the abomasum, and ruminal drinking. 3.11.12 Ruminal drinking is seen in veal caves and results in cachexia, chronic ruminal tympany, malabsorption, small intestinal villous atrophy, anemia, ventral abdominal distention, and clay-like feces. 3 It is caused by a failure of closure of the reticular groove, so that ingested milk enters the ruminoreticulum, where it remains for over 48 hours. There, it is partially digested, which prevents normal casein clot formation when the milk enters the abomasum. Affected animals do not gain weight normally. They may be treated by feeding with a bottle or by placing a floating nipple in the bucket rather than allowing them to drink without sucking. The sucking motion is thought to be important in inducing reticular groove closure. If unresponsive to medical therapy, recurrent tympany can be treated by creating a temporary rumen fistula in the left flank.21 With the calf under local anesthesia, a 5-cm circle of skin is removed from the dorsal left flank. The muscle layers are separated in a grid fashion and the peritoneum is incised, exposing the rumen. To avoid contamination of the abdomen, the rumen may then be sutured to the subcutaneous tissue. A circle of the rumen wall is then excised, and the cut

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Figure 1. Free gas bloat in a young heifer. (Courtesy of Dr. Robert Whitlock.)

edge of the rumen is sutured to the skin. The separated muscle layers act as a valve to prevent leakage of rumen contents, but allow escape of gas when high intraruminal pressure occurs. The fistula can be expected to remain patent for 1 to 2 months. Traumatic reticulitis is rare in calves but does occur.50 Signs are similar to those seen in adults, with the presence of postxyphoid pain, abducted elbows, fever, and neutrophilia. Foreign bodies may be removed by reticulotomy via a ventral or paracostal approach. 50

ABOMASAL DISORDERS

Conditions affecting the abomasum of calves that may benefit by surgical intervention include abomasal ulcers, abomasal displacement or volvulus, abomasal incarceration, and abomasal outflow obstruction. Abomasal Ulcers Abomasal ulcers (Fig. 2) and abomasal displacements may occur individually or concurrently in young calves. The peak incidence of abomasal ulcers occurs at approximately 3 to 4 months of age. 53 Multiple etiologies have been proposed, including stress, availability of coarse straw, Clostridium perfringens type A,51,52 intrauterine or neonatal fungal infections,19.70 and changes in diet from milk to coarse feed. 37 Although the incidence of abomasal ulcers is high, approaching 100 per cent in some studies,53,66 they rarely perforate. Perforation can lead to either localized or generalized peritonitis. Animals with small

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Figure 2. Perforating abomasal ulcer. (Courtesy of Dr.

David Kradel.)

perforations and localized peritonitis may survive the incident. Animals with generalized peritonitis quickly deteriorate. Few affected animals show abdominal pain. 62 Most have a history of being found recumbent, often only a few hours after normal feeding. 62 Physical parameters reHect hypovolemic shock, with hypothermia, increased heart rate, pale mucous membranes, and prolonged capillary refill times. Animals are often moribund at the time of examination. Peritonitis can be diagnosed based on abnormal peritoneal fluid. In severe cases, straw, hair, and milk may be recovered from the peritoneal cavity. Affected animals should be rapidly rehydrated, started on broadspectrum antibiotic therapy, and prepared for a right paracostal or right paramedian laparotomy. From either approach, the abomasum is exteriorized as much as possible, and the area of the ulcer is isolated from the rest of the surgical field. The ulcer is then sharply resected and oversewn with an inverting pattern of absorbable suture material. The peritoneal cavity must be copiously lavaged with warmed isotonic Huids. 62 Antibiotics should be continued for several days after surgery, and Huid therapy should be continued until the animal is able to maintain normal hydration. Abomasal Displacement or Volvulus Abomasal displacements in calves may be to the right or left, though it is this author's experience that right-sided abomasal volvulus is more common than left displacements. This may be a reHection of a university hospital caseload or that left displacements are often con-

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fused with ruminal tympany and, therefore, are not examined by veterinarians. The cause of abomasal displacements in calves is unknown. Interestingly, several calves with abomasal volvulus have presented with a history of ingestion of a large meal followed by lively exercise. Abomasal emptying is controlled in part by the contents of the duodenum. Acid infusion into the duodenum causes inhibition of antral motility and decreased emptying. 56 Infusions of sodium bicarbonate, sucrose, butterfat, or hyperosmolar sodium chloride into the duodenum increase gastric emptying. 56 Calves may develop abomasal displacement or volvulus at a very young age. There are several reports of affected calves under 2 months 0Id.l.16.30.38.39 Calves with abomasal volvulus have abdominal distention and may exhibit significant abdominal pain and odontoprisis. Dehydration occurs relatively rapidly. A large area of tympany can be noted on simultaneous auscultation and percussion of the right flank. Prior to starting surgery, fluid deficits should be addressed and antibiotics should be instituted. Ulcers have been observed associated with abomasal displacements in calves; 1 therefore, surgery should be viewed as a potentially nonsterile procedure. Correction of right abomasal displacements may be approached through the right flank, right paramedian, or right paracostal approaches. The right flank and right paramedian approaches are identical to those described for adults, and the reader is referred to the article by Dr. Trent for a description of these procedures. The paracostal approach offers excellent exposure of the calf's abomasum. The calf is sedated if indicated and restrained in left lateral recumbency. If severe abdominal distention is present, oxygen may be administered by nasal insuffiation. A local block is performed just caudal to the last ribs and their costal cartilages. A I5-cm incision is made just caudal to the line of infiltration. Segmental nerves may be retracted. Upon opening the abdomen, the surgeon should note whether air is aspirated into the peritoneal cavity. If not, the abomasum should be examined carefully for ulcers. The peritoneal fluid should also be examined at this time. Fibrin accumulation is an indication of severe intra-abdominal inflammation, the source of which must be determined. In calves with abomasal displacements, fibrin accumulation may be indicative of concurrent abomasal ulcers or ischemic damage to the abomasal wall. This type of ischemic damage occurs during abomasal volvulus that obstructs the abomasal vasculature. By palpating on the craniomedial side of the abomasum, the surgeon can determine the direction of the volvulus. In calves it is almost always possible to reduce the volvulus without performing an abomaso to my for fluid removal. If the abomasum is greatly distended, gas can be removed using a 14-gauge needle and sterile tubing. The tubing ensures that any fluid that may exit through the needle does not contaminate the abdomen. After the gas is aspirated, the volvulus is reduced and the abomasal serosa is examined for evidence of necrosis or ulceration. Ulcerated areas may be resected or simply oversewn, depending on their extent.

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An abomasopexy is then performed to prevent future recurrence of abomasal displacement. Several sutures are placed through the seromuscular layers of the abomasum, just lateral to the attachment of the greater omentum, and into the cranioventral body wall, just to the right of midline. All sutures should be preplaced, then sequentially tied. A multifilament nonabsorbable suture material would be expected to result in the strongest adhesions. 59 If fibrin is observed within the abdominal cavity, or if there is any possibility of leakage from the abomasum through needle holes or ulcers, the abdomen should be lavaged with isotonic fluids prior to routine closure of the laparotomy incision. Left displacement of the abomasum (LDA) may be seen in calves, usually after 8 weeks of age. Affected animals have left-sided abdominal distention. Unlike adults, in which the left paralumbar fossa often appears sunken because of medial displacement of the rumen, calves with LDA often have a bulging left paralumbar fossa. 1o This is a result of the relatively large abomasum in calves. Other physical findings include poor condition, depression, bradycardia, and cranial abdominal pain. 10 Abomasal ulcers are often associated with left abomasal displacement, and their presence indicates a poor prognosis. 10,24 Aspiration of luminal contents through the eleventh intercostal space may be used to differentiate the abomasum from the rumen, as is done in adults. In addition, calves that retain a reticular groove reflex may be examined by contrast radiography after suckling contrast materia1. 24 Any of the approaches to correction of an LDA in adults is acceptable in calves with uncomplicated LDA. If abomasal ulcers are present, a left paralumbar fossa or right paramedian approach should be used. The specifics of abomasal fixation can be found in the article by Dr. Trent. Abomasal Incarceration The abomasum is the most common organ involved in umbilical hernias, and it may become incarcerated in that location. 15 Usually partial herniation has no observed detrimental effect on the calf, although abomaso-umbilical fistula may occur. 18,45 Affected calves have obvious leakage of abomasal fluid through the defect, resulting in hypochloremic metabolic alkalosis. The alkalosis may be treated by appropriate intravenous fluid therapy or by eliminating leakage with a bandage. Prior to initiating surgery, broad-spectrum antibiotic therapy is instituted. The calf is cast in dorsal recumbency under sedation if necessary, and local anesthesia is used. An elliptical incision is made around the umbilical hernia, including the fistula. An en bloc resection of the involved body wall is performed. It is especially important to use care when entering the peritoneal cavity, as there may be extensive adhesions of the abomasum to the body wall. After dissecting to normal abomasal tissue surrounding the fistula, the involved abomasum and body wall are removed. The cut edges of the abomasum are lavaged, then closed with a double inverting suture pattern. If the body wall

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appears contaminated, through and through sutures of monofilament steel may be used in a single layer closure. Otherwise, a routine layer by layer closure with monofilament material can be completed. Acidbase and electrolyte abnormalities quickly return to normal after closure of the defect. Abomasal Outflow Obstruction Partial abomasal outflow obstruction may occur from ingestion of extremely fibrous material, hair, or other indigestible material. Hairballs occur in calves as a result of a number of causes. Fiber poor diets, hot weather with increased sweating, salt deficiency, the suckle reflex, and ectoparasites may all contribute to hairball development. 6 Because of the function of the esophageal groove, most ingested hair accumulates in the abomasum. Once they develop, hairballs can result in intermittent abomasal obstruction with secondary bloat and decreased fecal output. 27 Other associated clinical signs include odontoprisis, abnormal gait, indigestion, and general poor condition. 6 If obstruction occurs, the hairballs may be removed by abomasotomy. 11,12,27,32 Antibiotics are given preoperatively, as this procedure may contaminate the peritoneal cavity. A ventral, right paramedian, or right paracostallaparotomy may be used. The abomasum is partially exteriorized and packed off from the rest of the abdomen before the abomasotomy is performed. After removal of the hairballs, the edges of the abomasotomy are lavaged, and a two-layer inverting closure is performed. The abomasum should be lavaged again before it is returned to the abdomen. SURGERY OF THE SMALL INTESTINE

Disorders of the small intestine requiring surgical correction include intestinal incarceration, strangulation, intussusception, volvulus of the root of the mesentery, and atresia of the jejunum. Disorders of the small intestine are best approached through a right flank laparotomy, as is true in adults. With all the above disorders, abdominal enlargement due to small intestinal distention is expected. Multiple, variably pitched areas of tympany may be detected by simultaneous auscultation and percussion of the right flank. Dehydration occurs secondary to sequestration of fluids within the intestinal tract. As in adult cattle, calves with intestinal obstruction soon develop hypokalemic, hypochloremic metabolic alkalosis. 23 Intestinal incarceration may occur secondary to adhesions of intestine to remnants of the ductus deferens in yearling steers.69 This is associated with castration at greater than lOO-kg body weight. Signs are consistent with a gradual obstruction, with decreasing fecal production, appetite, and alertness. Dilated small intestine may be palpated on examination of the abdomen per rectum if the steer is large enough for this procedure. Affected intestine may not be necrotic, and resection of the adhesion to the ductus may be sufficient for recovery.

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Animals with intestinal strangulation have a more rapid onset and more severe presentation of clinical signs than those with intestinal incarceration. Because of devitalization of intestine, a leukocytosis and hyperfibrinoginemia may be present. 28 Affected calves gradually become moribund if not promptly treated. Surgical treatment is similar to that of adults. Intussusceptions (Fig. 3) result in intestinal obstruction, often without evidence of severe inflammation in the peritoneal cavity. Signs include sudden anorexia, dehydration, abdominal pain,5,13 and lack of feces (Fig. 4). Progression of signs is generally slower than in animals with intestinal strangulation. Intussusceptions may occur throughout the small or large intestine in calves, unlike adult cattle, in which intussusceptions usually occur in the jejunum. 17 Treatment is similar to that for adults. Volvulus of the mesenteric root has been reported in calves as young as 12 hours of age. It results in the rapid demise of the animal. Abdominal pain, abdominal distention, severe shock, anorexia, tachycardia, and lack of defecation occur. 61 Correction of the fluid deficit and the volvulus must be accomplished rapidly. The direction of the volvulus can be determined by palpation of the mesentery. The intestine should be rotated in the same direction as the surgeon's hand turns as it is moved along the mesentery toward the root. In addition to intravenous fluids and antibiotics, antiendotoxin therapy is probably indicated in affected calves. Atresia of the small intestine has been observed in several breeds of cattle (Fig. 5). It has been reported to be caused by a recessive gene

Figure 3. Necropsy specimen: intussusception of the jejunum in a young calf. Visible are the darkened, distended jejunum proximal to the intussusception (large arrow), the coiled intussusception (small arrow), and the collapsed intestine distal to the intussusception (arrowhead). (From Fubini SL: Gastrointestinal obstructions in calves. Comp Cont Ed Pract Vet, in press; with permission.)

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Figure 4. Heifer exhibiting abdominal pain from an intussusception. Treading of the hind feet, kicking at the abdomen, and recurrent recumbency also may be observed. (Courtesy of Dr. Robert Whitlock.)

in Jerseys, although no substantiation of this claim could be found. 2 Successful repair of this defect in calves has not been reported. Atresia of the ileum occurred in inbred Swedish Highland cattle. Affected calves are aborted late in gestation with extremely dilated abdomens, resulting in distocia. 47 It is unknown why intrauterine abdominal distention occurred in these calves, when it is not observed in cattle with atresia of the jejunum or colon.

SURGERY OF THE LARGE INTESTINE

Disorders of calves' large intestine requiring surgery for correction include cecal torsion, 9 intussusception,22 and colonic atresia. Diagnosis and treatment of cecal torsion are similar in calves and adults and are discussed in the article by Dr. Fubini. Intussusception of the large intestine is seen in calves but not adult cattle. This is probably due to calves' general lack of mesenteric fat, which allows greater mobility to the intestine. In adult cattle, the fat-filled mesentery maintains the relationship of the various segments of the large intestine, thus preventing the occurrence of intussusception in this location. Surgical resection of a large intestinal intussusception must be done with care not to disturb the vascular supply to adjoining intestine. In one description, a bovine large intestinal intussusception was manually reduced and short devitalized areas were removed, thus avoiding mesenteric dissection. 22 Reduction of intussusceptions is dangerous, as they may rupture, and it also does not eliminate any predisposing cause, such as intraluminal or mural masses.

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A

).~

rr· .. .• .•. _ .• . •. i •......•.. •...•. . . . c ..... .•..

Figure 5. A, Atresia of the jejunum in a 3-day-old Jersey heifer. The jejunum proximal to the site of the atresia is greatly distended (arrows). The jejunum distal to the atresia is smaller than normal and collapsed (arrowheads). B, Close-up of site of atresia. Because there is no mesenteric defect, this would be classified as a type II atresia of the jejunum (see discussion of atresia coli). (Courtesy of Dr. Elaine Hunt.)

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Atresia of the intestine (Fig. 6) is the most commonly reported cause of gastrointestinal obstruction in the calf. * It has classically been divided into several types. Type I atresia includes intestine whose patency is interrupted by a diaphragm of tissue. In type II atresia, the proximal and distal blind ends of the intestine are attached by a cord of intestinal remnant. In type III intestinal atresia, the two blind ends are separated by a mesenteric gap. Intestinal atresia in cattle usually occurs within the spiral portion of the ascending colon. Because the entire spiral colon shares a common mesentery, the intestinal atresia observed in calves does not fit neatly into the above classification scheme. Usually, the two blind ends are not attached by a cord of tissue, and there is no mesenteric gap observed. Several syndromes of intestinal atresia that have been described in humans have not been reported in cattle. The pathogenesis of intestinal atresia in cattle has not been definitely determined, although the disorder is seen more frequently in herds in which pregnancy diagnosis is made by palpation of the amniotic vesicle at less than 42 days of gestation. 42,44 The disease has been created experimentally in many species by interruption of the vascular supply to a portion of the intestine either in utero or in ovo. It has also been observed in a human infant whose mother used a vasoconstrictive drug during pregnancy and in both of a set of twins whose mother suffered a drug-induced anaphylactic reaction at 10 1/2 weeks' gestation. 2o,48 In humans, the intestine is particularly sensitive to vascular compromise between 10 and 12 weeks' gestation. 48 An acquired lesion clinically similar to intestinal atresia was observed in a 19-month-old boy on total parenteral nutrition for 2 months. During treatment, a portion of the bowel strangulated and was resorbed. 40 There are multiple syndromes of intestinal atresia in humans, only some of which have -References 7,14,25,29,33,36,42 - 44,47,49,55,58,60,64.

Figure 6. Atresia of the proximal part of the ascending colon (arrow). The cecum is distended with meconium.

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a genetic basis. In calves, intestinal atresia has been reported in one of a set of twin calves, arguing against a hereditary cause in that instance. 25 In humans, duodenal atresia is often associated with other abnormalities, while atresia of the intestine in other sites is not. Intestinal atresia is not usually associated with other defects in calves, although in one report, approximately 30 per cent of affected calves also had umbilical hernias. 14 Calves with intestinal atresia usually are presented to the veterinarian in the first week of life. The calves are born normally and have a history of nursing normally shortly after birth. Over the next few days, the calves gradually deteriorate. Partial to complete anorexia, increasing abdominal distention, and depression leading to a moribund state occur. No feces are passed. Unlike calves with atresia ani, tenesmus is not observed. Multiple, variable pitched "pings" may be elicited by simultaneous auscultation and percussion of the right flank. Dilation of the cecum and proximal spiral colon can be detected by careful abdominal palpation. Peritoneal fluid analysis and the leukogram will vary depending on the degree of necrosis of the proximal blind end of the intestine. The plasma total protein may appear normal on initial evaluation because of a combination of dehydration and hypoproteinemia. Despite the usual history of "adequate" colostral intake, affected calves are often hypogammaglobulinemic. In a prospective study, 30.7 per cent of affected animals had low IgG levels. 14 It has been theorized that absorption of colostral antibodies is abnormal in this condition as a result of decreased intestinal surface area for absorption and decreased total colostral intake. 58 As most absorption of gamma globulins occurs in the proximal small intestine of cattle, it would be expected that the intestinal surface area for absorption would be normal in calves with atresia coli, unless there are also small intestinal villus abnormalities. The decreased absorption may be due to decreased intake or decreased exposure of ingested colostrum to the intestinal epithelium during the critical period for immunoglobulin absorption. Decreased exposure of ingested colostrum to the intestinal epithelium may be caused by ileus secondary to the obstruction. Calves with atresia coli should be treated by rehydration, initiation of antibiotic therapy, and surgical correction of the abnormality. Surgery should not be delayed, as the risk of peritonitis increases with time (Fig. 7). The goals of surgical therapy are to remove meconium from the proximal intestine (Fig. 8), to remove the proximal blind loop to intestine of fairly normal diameter (Fig. 9), and to reestablish continuity of the intestinal tract. Upon opening the abdomen via the right flank, gross distention of the cecum, proximal spiral colon, and small intestine will be observed (see Fig. 6). Gas distention of the large colon may be relieved by aspiration to prevent rupture of the large colon during manipulation. If distention of the large colon with meconium is severe, a typhylotomy (cecotomy) should be performed (see Fig. 8). The cecum is exteriorized and packed off from the remainder of the abdomen. Two stay sutures are placed in the apex of the cecum, and an incision is made between these sutures.

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Figure 7. Fibrinous peritonitis and cecal necrosis secondary to atresia of the spiral colon. The proximal blind end of the spiral colon is in the surgeon's left hand. The necrotic portion of the cecum is yellow and appears blanched in the photograph.

Contents of the cecum and proximal spiral colon are milked through the enterotomy. The typhylotomy is routinely closed after thorough lavage. The site is again lavaged after closure, prior to continuing with the procedure. The proximal blind end of the spiral colon is removed, as experimental studies have shown in other species that the bowel adapts to high pressure and is inefficient at transport of its contents when normal pressure is restored. 67 The dilated intestine should be removed proximally to a segment of large intestine with normal diameter that can be approximated to the descending colon. The proximal blind end of the spiral colon is identified and dissected free from the common mesentery. Vessels should be ligated or cauterized close to the bowel being excised to avoid impairing jejunal blood supply (see Fig. 9). In calves

Figure 8. Meconium may be removed by an enterotomy at the cecal apex. Meconium should always be removed as part of the surgical procedure because its tenacity can cause obstruction of the anastomosis.

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Figure 9. The proximal blind end has been dissected free of its mesenteric attachments prior to resection. Note that dissection was performed close to the colon to avoid disrupting the vascular supply to the adjacent intestine.

without severe large colon distention, the typhylotomy can be omitted, but the meconium must still be removed as its tenacious nature can lead to anastomotic failure. In these calves, once the proximal blind end is dissected free of the mesentery, an enterotomy is performed at its apex, through which the large intestinal contents are removed. The proximal blind end is then resected at its remaining mesenteric attachment. Contamination can be minimized by use of an autosuturing instrument (TA 55, TA 90, or CIA, United States Surgical Corp., Norwalk, CT 06856). A lubricated soft rubber catheter is then inserted into the descending colon per rectum. The wall of the descending colon is extremely thin, presumably because of disuse atrophy. A side-to-side or end-toside anastomosis of the new proximal blind end and the descending colon is created. The author prefers a stapled side-to-side anastomosis, as it can be completed quickly and cleanly. Alternatively, a single layer handsewn anastomosis is satisfactory. After completion, the anastomosis should be checked for leaks and patency. The area is then lavaged before routine closure of the abdomen. The proximal blind end of the colon is anastomosed to the descending colon rather than the atrophied distal blind end because the functional capacity of the distal portion of the bowel is presumed to be poor, it is often difficult to locate, and there may be more than one site

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of atresia. 58 Short-term complications of the surgery include anastomosis failure, diarrhea, impaction, incisional infections, and respiratory infections.14 Long-term complications are infrequent, but include intestinal obstruction secondary to adhesion formation, slow growth, incisional abscesses, and chronic cecal dilatation 14 (Fig. 10).

SURGERY OF THE RECTUM AND ANUS

Atresia ani is an easily diagnosed abnormality (Fig. 11). Affected calves pass no feces and exhibit tenesmus and gradually increasing abdominal distention. Surgical correction depends on the sex of the animal and on the extent of rectal involvement. Most female calves with atresia ani also have fistula formation between the rectum and reproductive tract, most frequently the vagina. In males, the rectum may communicate with the urethra or bladder.57,6o The perineal region should be observed during periods of tenesmus or while compressing the calf's abdomen. If only the anus is involved, a distinct bulge will be observed as the rectum pushes against the perineal skin. If no bulge is observed, atresia of the caudal rectum is presumed. The degree of involvement can be determined by radiography. A coin or other radiodense object is taped in the normal anal location. The animal is then lifted by its hindlimbs, and a lateral radio-

Figure 10. Intestinal tract of a Holstein heifer 4 months after repair of atresia coli. The heifer was euthanatized because of Salmonella sp. infection. The forceps identifies the pylorus. Adhesions to the cecum and a large mesenteric defect are present. The calf was growing normally but was euthanatized to prevent spread of salmonella.

Figure 11. A, Atresia ani, atresia recti, and taillessness in a Jersey calf. B, On compression of the abdomen, a slight bulge was noted in the dorsal perineal area. After routine surgical preparation, an elliptical incision is made in this area. C, By blunt dissection, the distal colon and proximal rectum are isolated and elevated through the incision. The rectum is circumferentially sutured to the subcutaneous tissue prior to incising it. The cut edge of the rectum then is sutured to the skin. D, Site 2 weeks after surgery.

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graph is taken. This positioning of the animal fills the caudal rectum with gas, simplifying determination of the extent of the defect. Simple anal atresia is corrected by making a circular incision in the skin and subcutaneous tissue in the normal anal location. To avoid contamination, the caudal rectum may be sutured to the subcutaneous tissue at this point. The rectum is then incised and the cut edges are sutured to the skin. Single stab incisions through the perineum into the rectum are contraindicated, as they will stricture and result in obstruction. If the caudal rectum is also absent, a rectal pull-through must be performed. This is often the case in calves that also have sacral abnormalities and no tail. A circular incision is made in the perineal skin and subcutaneous tissue. Blunt dissection is used to identify the caudal rectum. It is then pulled caudally to the skin incision. The procedure is completed as described above. In calves with communication of the rectum and urogenital tract, the fistulas must be isolated and closed. Separation of the rectum and urogenital structures, with separate closure of the two resultant defects, is usually satisfactory. If the uterus has filled with meconium, it may be temporarily marsupialized to allow drainage. If much of the rectum and caudal descending colon is absent, a colostomy may be performed as a salvage procedure. This is rarely performed in cattle. DIAPHRAGMATIC HERNIATION

Several calves with diaphragmatic hernias have been reported. 4 ,26,41,63 Diaphragmatic defects may be congenital or the result of trauma. Congenital defects are usually peritoneal pericardial diaphragmatic hernias. 27 Signs may include weakness, respiratory distress, slight coughing, odontoprisis, recurrent bloat, capricious appetite, or lack of normal lung sounds. Successful repair of congenital peritoneal pericardial hernias in calves has not been reported to the authors' knowledge. Traumatic rupture of the diaphragm may be repaired through a ventral approach. If the calf is old enough to ruminate, the rumen should be emptied through a rumenotomy prior to attempting repair of the diaphragm. Mesh implants may be used if the diaphragmatic defect is large. 63

SUMMARY Many disorders of the calf's gastrointestinal tract require surgical intervention if a successful outcome is to be obtained. The most common abnormalities in this category are abomasal volvulus, abomasal ulcers, small intestinal accidents, and atresia of the spiral colon. These can be differentiated by the age of the animal at presentation and a careful physical examination. Special considerations in neonatal gastro-

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intestinal surgery include: ensuring adequate serum immunoglobulin status, rapid treatment of dehydration and hypoglycemia, and consideration of the inheritability of any corrected defects. Prompt attention to metabolic disturbances and correction of the abnormalities are essential for a successful outcome.

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Address reprint requests to David G. Bristol, DVM College of Veterinary Medicine North Carolina State University Raleigh, NC 27606