Materials and Methods

Animals—The study involved 30 lactating dairy cows (German Black Pied crossed with Holstein-Friesian) that were admitted to the Leipzig University Veterinary Hospital for surgical correction of LDA. Mean ± SD age of the cows was 3.7 ± 1.8 years (mean parity, 1.9 ± 1.1), and they had been lactating for 25 ± 19 days. Left displaced abomasum was defined as displacement of the abomasal body to the left dorsal abdominal quadrant between the left body wall and rumen. A routine physical examination was performed on admission, including determination of rectal temperature, respiratory rate, heart rate, and body weight. A preliminary diagnosis of LDA was made on the basis of results of physical examination (simultaneous percussion and auscultation of the left side of the abdomen), and the diagnosis was confirmed at surgery. Cows with rectal temperatures > 39.5°C (103.1°F), clinical mastitis, watery diarrhea, retained fetal membranes, or evidence of peritonitis during surgery were excluded from the study. The study protocol was approved by an institutional animal use and protection committee, and owner consent was obtained when cows were admitted to the hospital.

Hematologic and serum biochemical analyses—Jugular venous blood samples were obtained when cows were admitted to the hospital. Each sample was analyzed for a CBC (including differential WBC count) and serum concentrations of total protein, glucose, total bilirubin, urea, E-hydroxybutyrate, and total calcium, by means of automatic analyzers.^a,b These analyses were performed to ensure that the groups did not differ with respect to these values and to identify cows with a systemic inflammatory process or metabolic disorder that may influence abomasal emptying rate.^25–27 Laboratory findings that resulted in additional exclusion of cows from the study were leukopenia (< 4,000 WBCs/PL), leukocytosis (> 13,000 WBCs/PL), hypocalcemia (serum total calcium concentration, < 2.0 mmol/L), hyperglycemia (serum glucose concentration, > 7 mmol/L), or azotemia (serum urea nitrogen concentration, > 7 mmol/L).

Experimental protocol—Cows arrived at the veterinary hospital during late afternoon or evening. A 14-gauge, 20-cm IV catheter^c was placed aseptically in the left jugular vein of each cow. This IV catheter was used for drug administration, fluid infusion, and periodic collection of blood samples for determination of serum D-xylose concentration. Ten liters of physiologic saline (0.9% NaCl) solution^d mixed with a 40% glucose solution^d to contain 700 g of glucose was administered IV to each cow overnight. All cows received an IV injection of the NSAID metamizol sodium^e (20 mg/kg [9.1 mg/lb]) and oxytetracycline^f (5 mg/kg [2.3 mg/lb]) 1 hour before surgery.

Cows were alternately allocated to 1 of 2 surgery groups (abomasopexy⁸ or omentopexy⁷; n = 15 cows/group) according to the order of admission, and the first cow of the study was assigned by means of flipping a coin. A D-xylose^g solution was prepared immediately before surgery by dissolving D-xylose in warm tap water to yield a 50% solution and stored for < 2 hours at 39°C (102°F) in a water bath before administration. Surgery was usually performed between 9 AM and 11 AM the following day by the same experienced surgeon (TW).

Two-step laparoscopy-guided abomasopexy—In the abomasopexy group, the skin of each cow was aseptically prepared at the site of trocar insertion, 10 mL of the local anesthetic procaine hydrochloride^h was infiltrated SC, and a stab incision was made in the left flank at the trocar insertion site. Filtered room air was introduced into the peritoneal cavity to create a pneumoperitoneum. The first step involved placement of a trocar into the greater curvature of the displaced abomasum and injection of the D-xylose solution (0.5 g/kg [0.23 g/lb]) into the abomasum with the cow standing.^9,28 A toggleⁱ was then placed into the abomasal lumen through the trocar, and the trocar was removed. The second step required positioning the unsedated cow in dorsal recumbency by use of a tiltable surgical table, which caused the abomasum to move toward the ventral abdominal wall. This movement was assumed to have resulted in a satisfactory mixing of D-xylose with the abomasal contents. The endoscope was then introduced through the left ventral abdominal wall, and the suture material attached to the toggle was identified and retrieved from the abdomen. Tightening of the toggle suture resulted in an abomasopexy to the right ventral abdominal wall in a typical location for the abomasum.²⁹

Omentopexy via right flank laparotomy—A right flank laparotomy was performed as described elsewhere.⁷ Briefly, skin of the right flank was aseptically prepared and regional anesthesia was achieved by infiltration with a 2% solution of procaine (100 mL) in an inverted-L block caudal the 13th rib. The procedure was performed with the cow standing. A 14-gauge needle attached to a flexible tube was inserted into the dorsal aspect of the abomasal lumen to inject D-xylose solution and to decompress the gas accumulated within the displaced abomasum. The abomasum was repositioned from the left to the right ventral portion of the abdomen, and this movement was considered sufficient to adequately mix the D-xylose solution with the abomasal contents. An omentopexy was performed approximately 4 to 6 cm caudal to the pylorus. The laparotomy incision was closed routinely. The interval from the first incision to last suture was recorded for both methods.

Postsurgical procedures—Intravenous infusion with physiologic saline solution (10 L) and glucose (700 g) every 12 hours was continued after surgery for 48 hours. Cows were fed grass silage, hay, and commercially available feed concentrates. Rumen motility (rumen contractions within 3 minutes determined by means of rumen auscultation) was determined each morning for 3 days after the day of surgery (day 0) by a veterinarian who did not take part in the study. Daily milk yield (from twice-daily milking) was recorded for 3 days after day 0. Because the surgical group to which cows were assigned was obvious, it was not possible to prevent the personnel who performed postoperative physical examinations and milking from being aware of treatment received.

Samples of jugular venous blood were obtained via the IV catheter after discarding the first 5 mL. Blood samples (5 mL) were collected into plain tubes immediately before D-xylose administration (0 minutes) and at 30, 60, 90, 120, 150, 180, 240, 300, 360, 480, 600, and 720 minutes after D-xylose administration and allowed to clot at 4°C (39°F) for 30 minutes. Blood samples were centrifuged at 1,800 X g for 10 minutes. Serum was harvested and stored at −21°C (–6°F) for up to 3 months before determination of D-xylose concentration.

Determination of D-xylose concentration and pharmacokinetic modeling—Serum D-xylose concentration was measured with a spectrophotometric assay^j (665 nm). This method has been used in studies^18,19 in cattle and cannot differentiate between the pentose sugars D-xylose, D-arabinose, and D-ribose; however, because pentose sugars exist only in negligibly low concentrations in mammalian serum in physiologic conditions, the measured pentose sugar concentration reflects D-xylose concentration.³⁰

Values of C_max and T_max were obtained from the serum D-xylose concentration versus time data of each cow. The serum D-xylose concentration versus time curve was modeled by use of the first derivative of a Siegel modified power exponential formula as described elsewhere.³¹ This model has been used for data analysis in several studies^9,18,19,32 involving calves and adult cattle.

The first derivative of the modified power exponential formula yields the following equation³¹:

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in which C(t) is the serum D-xylose concentration at time t (minutes) and m, k, and β are constants. Constant m is the total cumulative recovery of D-xylose in millimoles when time is infinite, k is an estimate of the rate constant for abomasal emptying expressed in units of minutes⁻¹, and β provides an estimate of the duration of the lag phase before an exponential rate of emptying is reached. The T_max-model, a pharmacokinetic variable that most accurately characterizes abomasal emptying rate in adult horses^33,34 and suckling calves,³² was obtained by differentiating the first derivative equation and solving when the derivative equaled 0, at which time t was equal to T_max-model and T_max-model equaled ln(β)/k. The value for C_max-model was then calculated by applying the values for m, k, β, and t = T_max-model to the first derivative of the modified power exponential formula.³¹ Apparent oral bioavailability was calculated as m/D, in which D represents the dose of D-xylose administered.

Statistical analysis—Data are summarized as mean ± SD, and a value of P < 0.05 was considered significant for all analyses. Variables that were not normally distributed were logarithmically transformed before statistical analysis was performed. Pharmacokinetically determined values for C_max-model and T_max-model were obtained by means of nonlinear regression as described elsewhere.³² A t test was used to determine whether there was a significant effect of group on physical examination findings; erythron, leukon, and serum biochemical values; C_max; T_max; and the pharmacokinetically determined values C_max-model and T_max-model. Repeated-measures ANOVA was used to compare daily milk yield and rumen motility during the study period between treatment groups.^k

Results

Animals—Twenty-eight of the 30 cows with an LDA were successfully surgically treated with omentopexy via right flank laparotomy or 2-step laparoscopyguided abomasopexy and discharged from the hospital. One cow in each surgery group died or was euthanatized (both at day 7 after surgery) because of failure to respond to treatment and subsequent multiorgan failure. Necropsy revealed extensive hepatic lipidosis in both cows, and data from both were included in the statistical comparison.

The cows in the 2 surgery groups did not differ with respect to age, days in lactation, body weight, mean rectal temperature, heart rate, and respiratory rate before surgery (Table 1). Cows with an LDA had a moderate hyperbilirubinemia (reference range, 3 to 5 Pmol/L) and mild hyperglycemia (reference range, 2.5 to 3.5 mmol/L), with no differences between groups. Mean serum concentrations of total protein, urea nitrogen, and total calcium and RBC and WBC counts were similar for both groups, with mean values within the reference range. Surgical time was shorter (P < 0.001) in the abomasopexy group (23 ± 7 minutes) than that in the omentopexy group (43 ± 9 minutes).

Mean serum D-xylose concentration during the period evaluated was not significantly different between the abomasopexy and omentopexy groups at any point (Figure 1). Mean values for C_max and C_max-model were similar for both groups (Table 2). The T_max and T_max-model were significantly shorter in cows that were treated with abomasopexy, compared with values in cows that were treated with omentopexy. Mean values for k, β, m, and apparent oral availability were not different between the groups.

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Mean ± SD serum D-xylose concentrations in lactating dairy cows after surgical correction of LDA by means of 2-step laparoscopy-guided abomasopexy (n = 15) or omentopexy via right flank laparotomy (15). A 50% D-xylose solution (0.5 g/kg [0.23 g/lb]) was injected into the abomasal lumen during surgery (0 minutes).

Citation: Journal of the American Veterinary Medical Association 234, 5; 10.2460/javma.234.5.652

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Rumen contraction rate increased faster after surgery in cows in the abomasopexy group than in cows in the omentopexy group (Table 3). Significant differences in the rumen contraction rate were evident between surgical groups on all postoperative days, compared with the rate on the day of surgery (day 0). Milk yield increased after surgery in both groups. In the abomasopexy group, milk yield on each of the 3 days that followed surgery was significantly different from milk yield before surgery (day 0). In contrast, in the omentopexy group, milk yield did not significantly increase until day 3 after surgery (Figure 2). However, daily milk yield did not differ between the groups at any time during the study period.

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Daily mean ± SD milk yield in lactating dairy cows before (day 0) and after surgical correction of LDA by means of 2-step laparoscopy-guided abomasopexy (n = 15) or omentopexy via right flank laparotomy (15). Groups were not significantly different with respect to milk yield on any study day. *Value is significantly (P < 0.05) different, compared with that for day 0 in the same group.

Citation: Journal of the American Veterinary Medical Association 234, 5; 10.2460/javma.234.5.652

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Discussion

In the study reported here, the main finding was that abomasal emptying rate in the immediate postoperative period was faster in lactating dairy cows with an LDA that underwent 2-step laparoscopy-guided abomasopexy versus omentopexy via right flank laparotomy. This finding was consistent with findings of other studies involving humans²⁰ and dogs,^21–23 which revealed that minimally invasive surgical techniques decrease the severity and duration of gastrointestinal hypomotility in the immediate postoperative period.

The severity of gastrointestinal hypomotility is related to the extent of surgical manipulation and subsequent inflammatory response in sheep,³⁵ humans,³⁶ and laboratory animals.^15,37 It is therefore likely that minimization of mechanical manipulation to the abomasum, small intestine, and omentum during the laparoscopy-guided procedure is the main reason for the difference in abomasal emptying rate detected between surgical groups in the present study. Other possible reasons for the treatment effect are the shorter duration of laparoscopic surgery versus laparotomy in the present and other studies^24,l and smaller incision sites in cows undergoing the laparoscopy-guided procedure.

Comparison of the postoperative abomasal emptying rate of cows treated with abomasopexy or omentopexy with that of healthy dairy cows in early lactation without LDA (T_max-model, 107 ± 14 minutes [n = 21 cows])⁹ suggests that abomasal emptying rate remained decreased after both surgical procedures. The value we obtained for T_max-model after omentopexy via right flank laparotomy (264 ± 94 minutes) was similar to values we obtained in 2 other studies^9,18 involving cows with an LDA in which omentopexy via right flank laparotomy was performed in similar conditions (T_max-model, 268 ± 55 minutes [n = 22 cows]; T_max-model, 277 ± 95 minutes [15]). Comparison of the postoperative abomasal emptying rates of the 2 surgical groups with the rate in cows with an LDA to which erythromycin (10 mg/kg [4.5 mg/lb], IM) was administered 60 minutes before omentopexy via right flank laparotomy (T_max-model, 149 ± 48 minutes)¹⁸ suggests that laparoscopic surgical methods can minimize postoperative hypomotility. This raises the question as to whether a combination of the laparoscopy-guided procedure and preoperative erythromycin treatment would have a synergistic effect on decreasing postoperative motility in cows with an LDA.

Amelioration of postoperative abomasal hypomotility in cows that have undergone surgical correction of LDA has been associated with improved clinical convalescence as assessed by postoperative feed intake, rumen motility, and milk yield.¹⁸ This amelioration might result in shorter duration of postoperative treatment and decreased costs for drug administration after laparoscopic surgery, compared with effects in cows treated by other means. Because of the identical treatment protocol and the standardized 4-day study period for all cows in the present study, this hypothesis was not tested. Milk yield and frequency of postoperative rumen contraction were recorded in a small number of cows. Although milk yield was not different between surgical groups during the study period, a postoperative increase in milk yield (ie, a significant difference compared with milk yield before surgery) was identified earlier in cows treated with 2-step laparoscopy-guided abomasopexy. Amelioration of postoperative abomasal hypomotility may be the reason for the superior clinical convalescence of cows after the laparoscopy-guided versus omentopexy procedure.^24,l

The results of the present study did not allow for conclusions regarding long-term outcome or differences between the surgical approaches with respect to long-term outcome. Although the personnel who measured and recorded the data could not be made unaware of the treatment assignment, our findings corroborated those of 2 other studies^24,l that revealed that endoscopy-guided abomasopexy results in improved convalescence during the immediate postoperative period. In those 2 studies, a superior outcome for cows that underwent laparoscopic surgery was detected during the 2 to 6 months after surgery, compared with the outcome in cows treated with right flank omentopexy. In contrast, a study³⁸ involving cows in which laparoscopy-guided abomasopexy and omentopexy via right flank laparotomy were performed on North American dairy farms did not identify differences in short- and long-term outcome and milk yield between procedures. However, cows in that study were not randomly assigned to the treatment groups, and consequently, results may have been biased.

On the basis of the results reported here, it is reasonable to assume that LDA-correction techniques that minimize manipulation of abdominal organs (eg, blind suture abomasopexy³⁹ or percutaneous bar suture abomasopexy⁴⁰) have similar effects on reducing postoperative abomasal hypomotility as reported here for the laparoscopy-guided procedure. Compared with laparoscopic surgery, the main disadvantage of the aforementioned percutaneous methods is that the fixation of the abomasum cannot be viewed. One-step laparoscopic methods in cows in dorsal recumbency⁴¹ and methods that avoid positioning cows in dorsal recumbency⁴² may be equal or superior to the 2-step perforating abomasopexy⁸ procedure in ameliorating postoperative abomasal hypomotility. It is unknown whether the nonperforating laparoscopy-guided⁴³ method, which is more time-consuming and requires considerable abomasal manipulations, has advantages not shared by techniques that require perforation of the abomasal wall.