Parenteral nutrition in the mature horse

Parenteral nutrition is an important component of the management of critically ill horses unable or unwilling to eat. It provides dextrose, amino acids, vitamins and minerals and, in some cases, lipids for nutritional support until enteral nutrition can be reinstituted. It can also be used as a supplement to enteral nutrition, where horses are not ingesting at least 80% of digestible energy (resting) requirements for more than 2–3 days. This review discusses the indications, applications, monitoring and complications of parenteral nutrition in mature horses.     

Nutritional and clinicopathological effects of post operative parenteral nutrition following small intestinal resection and anastomosis in the mature horse

REASONS FOR PERFORMING STUDY: There is an absence of data describing the nutritional requirements and nutritional status of horses following surgery for colic; furthermore, the potential effect of parenteral nutrition (PN) on improving nutritional status in such cases is unknown. HYPOTHESIS: Post operative colic cases suffer from a potentially detrimental negative energy balance and the PN formulation developed in this study would lead to clinicopathologically detectable improvements in the subjects' nutritional status. METHODS: Several clinicopathological variables, some known to be associated with nutritional status, were compared in 2 groups of horses in the post operative period following colic surgery; Group N (n = 15) were treated with PN and Group C (n = 15) were starved routinely. RESULTS: Group N had significantly lower serum concentrations of triglycerides, total bilirubin, albumin and urea and significantly higher serum concentrations of glucose and insulin compared with Group C in the post operative period. CONCLUSIONS: The control group of horses demonstrated significant clinicopathological evidence of starvation and the described PN protocol resulted in a demonstrably improved nutritional status in the treated horses. POTENTIAL RELEVANCE: Further study is required to investigate clinical benefits and possible harmful side effects of post operative parenteral nutrition before the technique can be advocated for widespread use in practice.     

Serologic testing of horses for granulocytic ehrlichiosis, using indirect fluorescent antibody staining and immunoblot analysis.

OBJECTIVE: To diagnose granulocytic ehrlichiosis in horses, compare results of indirect fluorescent antibody (IFA) staining procedures with those of immunoblot analysis, and compare serologic test findings with polymerase chain reaction (PCR) results. ANIMALS: 69 horses with high rectal temperatures (> or = 39 C) and lethargy, anorexia, or limb edema. PROCEDURE: 43 convalescent serum samples obtained from 38 horses 2 to 18 weeks after onset of illness were analyzed by use of immunoblot procedures and IFA staining methods, using the NCH-1 or BDS ehrlichial strains. Blood samples from 69 acutely ill horses were tested by PCR to detect ehrlichial DNA. RESULTS: Antibodies to Erlichial equi were detected in serum samples obtained during all seasons; seropositivity rates ranged from 50 to 93%. In IFA assays using the BDS or NCH-1 strain, seropositivity rates were 70 and 79%, respectively, whereas in immunoblot analyses using the NCH-1 strain, a seropositivity value of 79% was recorded. By immunoblot analysis, all serum samples of all seropositive horses were reactive to a protein having molecular mass of about 44 kd. Blood samples from 29 of 69 (42%) acutely ill horses contained ehrlichial DNA. CONCLUSION AND CLINICAL RELEVANCE: Results of the various serologic testing procedures were in close agreement with each other. All serologic testing methods are suitable for laboratory diagnosis of equine granulocytic ehrlichiosis.     

Serum bile acids concentrations in healthy and clinically ill neonatal foals

BACKGROUND: Reference ranges for serum bile acids (SBA) concentration are well established in healthy adult horses. Increased values are indicative of hepatic disease. HYPOTHESES: SBA concentrations are significantly greater in the neonatal period compared with mature horses, and illness in the neonatal period will further increase SBA. ANIMALS: Ten healthy mature horses, 12 healthy foals, and 31 clinically ill foals. METHODS: Prospective cross-sectional study. Blood samples were obtained once from the mature horses, from healthy foals immediately after birth, at 2 days, and at 1, 2, 3, 4, and 6 weeks of age; and from ill foals less than 1 month of age at the time of admission to the Veterinary Teaching Hospital. SBA concentrations were determined enzymatically and by radioimmunoassay. Total and direct bilirubin and triglyceride concentrations were measured, as well as sorbitol dehydrogenase (SDH) and gamma-glutamyltransferase (GGT) activities. RESULTS: There was a significant negative correlation between age and SBA concentration. Compared with mature horses, SBA concentrations were significantly greater in healthy foals at each collection time over the first 6 weeks of life. Radioimmunoassay values were lower than enzymatic SBA values, with increasing bias as the mean difference between values increased. When comparing age-matched values between healthy and ill foals, there were no significant differences in SBA. None of the ill foals had a primary diagnosis of hepatic disease. There was no significant correlation between the SBA concentration and the bilirubin or triglyceride concentrations or the GGT activity. There was a significant direct correlation between increased SBA and serum SDH activity in healthy foals only. CONCLUSION AND CLINICAL IMPORTANCE: SBA concentrations in foals are significantly higher in the early neonatal period, underscoring the importance of using age-matched references when evaluating clinical pathology values during the neonatal period.     

Measurement of free thyroxine concentration in horses by equilibrium dialysis

The purpose of the study reported here was to validate measurement of free thyroxine (fT4) concentration in equine serum by equilibrium dialysis (fT4D), and to compare values with fT4 concentration measured directly and with total T4 (TT4) concentration. The fT4D, fT4, and TT4 concentrations were measured over a range of values in euthyroid horses and horses made hypothyroid by administration of propylthiouracil (PTU). Concentrations of fT4D (<1.8-83 pmol/L) were consistently higher than those of fT4 (<1-40 pmol/L). There was a significant (P < .001) regression of fT4D on fT4 in 503 samples from normal horses (y = 2.086x - 0.430). In baseline samples from 71 healthy euthyroid horses, fT4 concentration ranged from 6-21 pmol/L (median, 11 pmol/L; 95% confidence interval [CI]10.5-11.8 pmol/L), and fT4D concentration ranged from 7-47 pmol/L (median, 22 pmol/L; 95% CI 20.9-25.1 pmol/L). Free T4D, fT4, and TT4 concentrations were also measured in 34 ill horses. Horses consuming PTU and ill horses had significantly (P < .05) lower serum concentration of TT4, fT4, and fT4D than did clinically normal, healthy horses. If serum samples from ill horses were further subdivided into samples from horses that lived and samples from horses that died, fT4D concentration was not significantly different in ill horses that lived, compared with that in healthy horses, whereas fT4 concentration was still significantly decreased in ill horses that died (P < 0.001). We conclude that measurement of fT4 concentration by equilibrium dialysis is a valid technique in the horse, and its use may provide improved ability to distinguish nonthyroidal illness syndrome from hypothyroidism in that species.     

Assessment of a point-of-care lactate monitor in emergency admissions of adult horses to a referral hospital

BACKGROUND: Blood lactate concentration [LAC] is considered a useful indicator of disease severity in horses. Agreement of point-of-care (POC) lactate monitors with laboratory standards has not been established for clinically abnormal horses. Hypothesis: It was hypothesized that results from a POC lactate monitor would be in agreement with a laboratory-based measurement of [LAC]. ANIMALS: The study included adult horses presented for emergency evaluation. METHODS: A prospective observational study was performed. [LAC] was measured with whole blood (AWB) and plasma (APL) by means of a POC monitor (Accutrend) and compared with results from whole blood measured by a laboratory blood gas analyzer (NOVA). RESULTS: Samples from 221 horses were used to compare the 2 lactate measurement techniques. Agreement (p +/- SE) was closest between APL and NOVA (0.97 +/- 0.01); an average observed difference of 0.15 +/- 0.89 (mean +/- SD) and 95% limits of agreement (LOA) -1.89, 1.59 also were found. Agreement was preserved and 95% LOA further decreased in horses with NOVA [LAC] of <5 mM and PCV <40%. Agreement was modest when testing whole blood samples on the POC monitor with increased 95% LOA. CONCLUSIONS AND CLINICAL IMPORTANCE: Results indicate close agreement between NOVA and the POC monitor when [LAC] was measured with plasma. Results were less consistent at higher [LAC] but sufficiently reliable to follow trends. Although whole blood may be used with the POC monitor to identify clinically important hyperlactatemia, results may be insufficiently reliable to monitor trends.     

Peroxidative protection of parenteral admixture by D-alpha-tocopherol

High lipid:low dextrose (HL:LD) parenteral admixtures (PAs) are becoming commonplace in the nutritional support of veterinary patients. Lipid peroxidation before administration appears to be an unwanted sequela of high lipid content in PAs that can lead to oxidative injury of biologic membranes in vivo. The purpose of this in vitro study was to measure hydroperoxides in HL:LD PAs and to determine the optimal dose of d-alpha-tocopherol to minimize peroxidation in these PAs during a 24-hr period. Detectable concentrations of hydroperoxides were present in all PAs. D-alpha-tocopherol appeared to significantly minimize peroxidation of HL:LD PAs in vitro. These results have clinical implications for parenteral feeding in critically ill patients.     

The lens and cataracts.

It is conservatively estimated that some form of lens opacity is present in 5% to 7% of horses with otherwise clinically normal eyes.These opacities can range from small epicapsular remnants of the fetal vasculature to dense and extensive cataract. A cataract is defined technically as any opacity or alteration in the optical homogeneity of the lens involving one or more of the following: anterior epithelium, capsule, cortex, or nucleus. In the horse, cataracts rarely involve the entire lens structure (ie, complete cataracts) and are more usually localized to one anatomic landmark or sector of the lens. Complete cataracts are invariably associated with overt and significant visual disability. Focal or incomplete cataracts alone seldom cause any apparent visual dysfunction in affected horses,however.     

Locomotor characteristics of horses with navicular disease

OBJECTIVE: To determine whether force-plate evaluation of horses with navicular disease would reveal an abnormal gait that persists despite loss of sensation to the palmar foot region, which may predispose such horses to navicular disease. ANIMALS: 17 clinically normal Thoroughbreds and 8 Thoroughbreds with navicular disease. PROCEDURE: Data on ground reaction forces were obtained in trotting horses, using a force plate. Force-time curve variables for clinically normal horses were derived from 4 points at the beginning and 4 points at the end of the vertical and craniocaudal horizontal plots. Principal component analysis was undertaken separately on beginning-of-stride and end-of-stride data, and the first 2 components were represented graphically. Rotation matrices were applied to equivalent data for horses with navicular disease before and after disruption of sensation by administration of a palmar digital nerve blockade. RESULTS: Prior to nerve block, horses with navicular disease differed significantly from normal horses for beginning-of-stance phase and end-of-stance phase variables. After nerve block, horses with navicular disease maintained the same significant differences from clinically normal horses only for variables at the beginning-of-stance phase. CONCLUSIONS AND CLINICAL RELEVANCE: Horses with navicular disease have abnormal limb-loading force patterns that are not altered by loss of sensation in the palmar region. These abnormal patterns were detected in a horse without navicular disease. Some horses are predisposed to navicular disease as a result of an inherent abnormal gait pattern. Analysis of gait patterns could be used for detection and appropriate management of horses susceptible to development of navicular disease.     

Role of bacteria in the pathogenesis of recurrent uveitis in horses from the southeastern United States

OBJECTIVE: To determine the role of intraocular bacteria in the pathogenesis of equine recurrent uveitis (ERU) in horses from the southeastern United States by evaluating affected eyes of horses with ERU for bacterial DNA and intraocular production of antibodies against Leptospira spp. SAMPLE POPULATION: Aqueous humor, vitreous humor, and serum samples of 24 clinically normal horses, 52 horses with ERU, and 17 horses with ocular inflammation not associated with ERU (ie, non-ERU inflammation). PROCEDURES: Ribosomal RNA quantitative PCR (real-time PCR) assay was used to detect bacterial DNA in aqueous humor and vitreous humor from clinically normal horses (n = 12) and horses with chronic (> 3-month) ERU (28). Aqueous humor and serum were also evaluated for anti-Leptospira antibody titers from clinically normal horses (n = 12), horses with non-ERU inflammation (17), and horses with confirmed chronic ERU (24). RESULTS: Bacterial DNA was not detected in aqueous humor or vitreous humor of horses with ERU or clinically normal horses. No significant difference was found in titers of anti-Leptospira antibodies in serum or aqueous humor among these 3 groups. Only 2 horses, 1 horse with ERU and 1 horse with non-ERU inflammation, had definitive intraocular production of antibodies against Leptospira organisms. CONCLUSIONS AND CLINICAL RELEVANCE: In horses from the southeastern United States, Leptospira organisms may have helped initiate ERU in some, but the continued presence of the organisms did not play a direct role in the pathogenesis of this recurrent disease.     

Assessment of a point-of-care test for measurement of blood triglyceride levels for rapid detection of equid hypertriglyceridaemia

This project investigated the clinical value of a human whole blood point-of-care (POC) triglyceride (TG) measurement device to determine equid blood TG concentrations. Equid plasma TG measurements were determined in a commercial laboratory and also using whole blood and plasma on the POC device from equid patients with TG concentrations from within the normal range to severely hypertriglyceridaemic. Results were compared between methods using the Bland-Altman method for validation. Seventy-four samples were collected: 35 from inappetent or starved equid patients (considered ‘at-risk’ of developing hypertriglyceridaemia) and 39 from equids eating with a normal appetite. The POC device readable range is 0.8–6.86 mmol/l; high readings were diluted and measurements repeated and calculated. Inappetent/starved patients had a higher risk of developing raised plasma triglycerides (OR 16.8, 95% CI 4.8–58.4, P<0.0001) than the appetent ones with 34% (12/35) having mildly increased TG and 31% (11/35) having moderately to severely increased TG concentrations. In comparison, there were no severely hypertriglyceridaemic patients, one moderately increased and 3/39 (8%) mildly elevated TG patients in the appetent group. In the readable range, using whole blood, the POC device had excellent agreement with the laboratory (mean difference -0.59). However, accuracy varied with TG concentration and the POC instrument overestimated TG values, particularly when TG values were above the POC device's range. For a given value in the readable range of the POC device, multiplication of the POC value by a factor of 0.77 (whole blood) and 0.72 (plasma) provides an estimation of the laboratory TG value. Whole blood TG readings below the POC instrument's range were reliably low. The POC device reliably predicted TG values in a clinical setting. Use of this device provides rapid, easy to perform, reliable assessment of blood TG concentration in equids at risk of developing hypertriglyceridaemia.     

Equine serum lipids: serum lipids and glucose in Morgan and Thoroughbred horses and Shetland ponies.

Concentrations of serum phospholipids, triglycerides, total cholesterol, nonesterified fatty acids, and glucose were determined for 9 months (September, 1972, to May, 1973) in 19 fasting horses and ponies (8 Morgan horses, 7 Thoroughbred horses, and 4 Shetland Ponies). Morgan horses had higher concentrations of total lipid than did Thoroughbreds, although the relative proportions of each type of lipid were similar in the 2 breeds. Shetland Ponies had higher nonesterified fatty acid and lower glucose concentrations than did either breed of horse. In both breeds of horses, concentrations of serum triglycerides in the cold months (December to March) were lower than those in the warm months. In the Shetland Pony, there was no seasonal variation in triglycerides, but a significant increase was seen in concentration of nonesterified fatty acids in the cold months. The significance of these findings is discussed.     

Serum tumor necrosis factor activity in horses with colic attributable to gastrointestinal tract disease.

Over a 24-month period, serum tumor necrosis factor (TNF) activity was determined in 289 horses with colic attributable to gastrointestinal tract disease. Serum TNF activity was quantitated by use of a modified in vitro cytotoxicity bioassay, using WEHI 164 clone-13 murine fibrosarcoma cells. Causes for colic, determined by clinical and laboratory evaluation, exploratory celiotomy, or necropsy included: gastrointestinal tract rupture (GTR); ileal impaction; small intestinal strangulating obstruction (SIO); proximal enteritis (PE); transient small intestinal distention; large-colon displacement; large-colon volvulus; large-colon impaction; colitis; small-colon obstruction; peritonitis; and unknown. Each diagnosis was placed into 1 of 3 lesion categories: inflammatory disorders (GTR, PE, colitis, peritonitis); strangulating intestinal obstruction (SIO, large-colon volvulus); and nonstrangulating intestinal obstruction (ileal impaction, transient small intestinal distension, large-colon displacement, large-colon impaction, small-colon obstruction, unknown). The prevalence of high serum TNF activity and/or mortality were evaluated. Differences were tested at significance level of P less than 0.05. Approximately 20% of the 289 horses has serum TNF activity greater than that found in clinically normal horses (greater than 2.5 U/ml). Twenty-three horses (8%) had marked increase in serum TNF activity (greater than or equal to 10 U/ml) which was more prevalent among horses with SIO and PE than in horses of other diagnostic groups, except those with GTR. Mortality and marked increase in serum TNF activity were greater in horses with intestinal inflammatory disorders or strangulating intestinal obstruction than in horses with nonstrangulating intestinal obstruction.(ABSTRACT TRUNCATED AT 250 WORDS)     

Rapid infusion of a phospholipid emulsion attenuates the effects of endotoxaemia in horses

REASONS FOR PERFORMING STUDY: Endotoxaemia currently is associated with a poor prognosis in horses. The results of recent trials in other species indicate that phospholipid emulsions reduce the deleterious effects of endotoxin (LPS). However, in a previous study in horses, a 2 h infusion of emulsion caused an unacceptable degree of haemolysis. HYPOTHESIS: Rapid administration of a lower total dose of emulsion would reduce the effects of LPS and induce less haemolysis; the emulsion would reduce inflammatory effects of LPS in vitro. METHODS: Twelve healthy horses received an i.v. infusion either of saline or a phospholipid emulsion (100 mg/kg), followed immediately by E. coli 055:B5 LPS (30 ng/kg). Clinical parameters, haematological profiles, serum tumour necrosis factor (TNF) activity, serum lipid profiles, urine analyses and severity of haemolysis were monitored before and at selected times after LPS. Monocytes were also incubated in vitro with LPS in the presence or absence of emulsion, after which TNF and tissue factor activities were determined. RESULTS: Clinical signs of endotoxaemia were reduced in horses receiving the emulsion, including clinical score, heart rate, rectal temperature, serum TNF activity, and the characteristic leucopenic response to LPS, when compared to horses not receiving the emulsion. Three horses receiving the emulsion had none, 2 had mild and one had moderate haemolysis. There were no differences in urinalysis results and creatinine concentrations, either within the groups over time or between the groups. Serum concentrations of phosphatidylcholine, bile acids and triglycerides peaked immediately after the infusion; there were no significant changes in concentrations of nonesterified fatty acids or cholesterol. Incubation of equine monocytes with emulsion prevented LPS-induced TNF and tissue factor activities. CONCLUSIONS: Rapid administration of emulsion significantly reduced inflammatory effects of LPS in vivo and caused a clinically insignificant degree of haemolysis. The results of the in vitro studies indicate that emulsion prevents not only LPS-induced synthesis of cytokines, but also expression of membrane-associated mediators (i.e. tissue factor). POTENTIAL RELEVANCE: Rapid i.v. administration of emulsions containing phospholipids that bind endotoxin may provide a clinically useful method of treating endotoxaemia in horses.     

Neurologic deficits associated with severe hyponatremia in 2 foals

Objective: To describe the neurologic deficits associated with profound hyponatremia in 2 critically ill foals. Series summary: A 4‐month‐old Thoroughbred colt and an 11‐day‐old Paint filly presented for acute diarrhea and depression. Severe neurologic deficits including blindness and head pressing were noted upon initial examination along with marked hyponatremia observed on biochemistry profile. Aggressive intravenous sodium replacement increased the serum sodium concentration to subnormal values with concurrent resolution of neurologic deficits. Intensive monitoring and fluid therapy were continued; the Thoroughbred colt was euthanized due to lack of response to the primary disease while the Paint filly was discharged clinically healthy without further complications. New or unique information provided: Mild hyponatremia (122–132 mEq/L) is a common clinicopathologic finding in equine medicine associated with a variety of diseases. The vast majority of horses with mild hyponatremia do not demonstrate direct clinical manifestations as a result of low serum sodium concentration. However, when severe acute hyponatremia occurs (<122 mEq/L), such as with acute enterocolitis, subtle to profound neurologic deficits may be observed and immediate and rapid treatment as well as serial evaluations of serum sodium concentration are warranted. Significant, and potentially permanent, neurologic deficits can occur if water balance and tonicity are not properly addressed. The cases presented here describe additional cases of a previously published disease in foals, acute hyponatremia and associated neurologic deficits, and describe the microscopic examination of the central nervous system in one foal that did not survive.     

Effect of experimentally induced endotoxemia on serum interleukin-6 activity in horses.

A study was conducted to determine whether serum interleukin-6 (IL-6) activity increased in horses during experimentally induced endotoxemia and whether serum IL-6 activity correlated to changes in clinical or laboratory data. Six clinically normal horses were given endotoxin IV (30 ng/kg of body weight) in 0.9% NaCl solution over 1 hour. Five of these and 1 additional horse served as controls and were given only 0.9% NaCl solution. Venous blood, for determination of serum IL-6 activity and WBC count, was collected before and at various times through 8 hours after the start of endotoxin or NaCl infusion. Rectal temperature and heart and respiratory rates were recorded throughout the study period. Serum IL-6 activity was determined by bioassay of proliferation of the B13.29 clone B.9 hybridoma cell line. From 1.5 through 5 hours after start of the infusion, serum IL-6 activity was significantly (P less than 0.05) increased in horses given endotoxin. Mean peak serum IL-6 activity was observed between 3 and 4 hours. In response to endotoxin infusion, horses became lethargic, tachycardic, and febrile. Leukopenia developed by 1 hour, followed by leukocytosis at 8 hours. Significant (P less than 0.05) positive association and linear correlation were apparent between mean serum IL-6 activity and mean rectal temperature in the group of horses that were given endotoxin. Changes from baseline were not evident in any of the clinical or laboratory values in horses given only NaCl solution.     

Cytological and microbiological findings in guttural pouch lavages of clinically normal horses with head restraint

OBJECTIVE: To evaluate the cytological and microbiological contents of guttural pouch washes of ten randomly selected horses restrained so as to prevent them lowering their heads, and to assess the possible effects on the guttural pouch environment in these horses. PROCEDURE: Cytological and microbiological studies were performed on guttural pouch washes of ten clinically normal horses restrained in a standing position so as to prevent them from lowering their heads below normal, as would happen during transportation on long journeys. They were restrained for 12 or 24 h and cytological, bacteriological and mycological findings in guttural pouch washes were recorded. RESULTS: The cytological gradings and neutrophil concentrations of guttural pouch washings were higher in horses that had their heads restrained for a longer period. Washings from these horses were more likely to contain cultivable bacteria and were the only washes yielding potentially pathogenic bacterial species. CONCLUSION: Variation in the cytological differential counts and bacterial cultures of guttural pouch lavages may be found in clinically normal horses which have had their heads restrained in an elevated position for periods from 12 to 24 h. This should be considered when examining this site and care must be taken when interpreting cytology of guttural pouch lavages in samples taken after transportation for more than 12 h. Restriction of head movement could also affect the normal pouch enviroment and predispose it to disease.     

Comparison of medical and surgical treatment for impaction of the small colon in horses: 84 cases (1986-1996)

OBJECTIVE: To characterize clinical findings and compare effects of treatment and outcome for horses treated medically or surgically for impaction of the small colon. DESIGN: Retrospective study. ANIMALS: 84 horses with impaction of the small colon. PROCEDURE: Medical records were reviewed for history, physical examination findings, laboratory values, treatment, response to treatment, complications, out-come, and necropsy findings. RESULTS: 47 horses were treated medically and 37 horses were treated surgically. Significant differences between groups were not identified for duration of clinical signs, physical examination findings, or laboratory values. Horses treated surgically were hospitalized longer than horses treated medically. Complications recorded during hospitalization included diarrhea, jugular thrombophlebitis, recurrent colic, fever, and laminitis. Salmonella organisms were isolated from 20 horses. Horses treated surgically were more likely to have signs of moderate abdominal pain, gross abdominal distention, and positive results for culture of Salmonella spp than horses treated medically. Follow-up information was available for 27 horses treated medically and 23 horses treated surgically. Twenty-four (72%) and 21 (75%) of the horses, respectively, survived and were being used for their intended purpose at least 1 year after treatment. CLINICAL IMPLICATIONS: Colitis may be a predisposing factor for impaction of the small colon in horses. Prognosis for horses treated surgically or medically is fair.     

Colloid Osmotic Pressure of Parenteral Nutrition Components and Intravenous Fluids

Objective: Parenteral nutrition is an important part of therapy for critically ill animals that cannot tolerate enteral feedings. It has been hypothesized that parenteral nutrition might also play a role in increasing colloid osmotic pressure (COP). The purpose of this study was to measure COP of various parenteral nutrition components and compare them to the COP of commonly used intravenous solutions.
Design: Membrane colloid osmometry was used to measure the COP of parenteral nutrition components (lipids, Abstractamino acids, dextrose solutions) and of synthetic colloids, crystalloids, and blood products.
Main Results: Parenteral nutrition components and all crystalloid solutions had COP measurements < 1 mm Hg. Great variation in COP was found in the different artificial colloids and blood products. The COP of the artificial colloids tested ranged from 32.7 ± 0.2 mm Hg for hetastarch to 61.7 ± 0.5 mm Hg for dextran 70.
Conclusions: The results of this in vitro study suggest that parenteral nutrition does not directly contribute to an increase in oncotic pressure. Further studies are needed to determine whether parenteral nutrition may indirectly influence COP in vivo. Knowing the COP of a fluid, along with its other properties, is useful in making appropriate therapeutic decisions.     

Measurement of C‐peptide concentrations and responses to somatostatin,glucose infusion,and insulin resistance in horses

Reasons for performing study: Hyperinsulinaemia is detected in horses with insulin resistance (IR) and has previously been attributed to increased pancreatic insulin secretion. Connecting peptide (C‐peptide) can be measured to assess pancreatic function because it is secreted in equimolar amounts with insulin and does not undergo hepatic clearance. Hypothesis: A human double antibody radioimmunoassay (RIA) detects C‐peptide in equine serum and concentrations would reflect responses to different stimuli and conditions. Methods: A validation procedure was performed to assess the RIA. Six mature mares were selected and somatostatin administered i.v. as a primed continuous rate infusion, followed by 50 nmol human C‐peptide i.v. Insulin and C‐peptide concentrations were measured in horses (n = 6) undergoing an insulin‐modified frequently sampled i.v. glucose tolerance test, and in horses with insulin resistance (n = 10) or normal insulin sensitivity (n = 20). Results: A human RIA was validated for use with equine sera. Endogenous C‐peptide secretion was suppressed by somatostatin and median (range) clearance rate was 0.83 (0.15–1.61) ml/min/kg bwt. Mean ± s.d. C‐peptide‐to‐insulin ratio significantly (P = 0.004) decreased during the glucose tolerance test from 3.60 ± 1.95 prior to infusion to 1.03 ± 0.18 during the first 20 min following dextrose administration. Median C‐peptide and insulin concentrations were 1.5‐ and 9.5‐fold higher, respectively in horses with IR, compared with healthy horses. Conclusions: Endogenous C‐peptide secretion decreases in response to somatostatin and increases after dextrose infusion. Results suggest that relative insulin clearance decreases as pancreatic secretion increases in response to dextrose infusion. Hyperinsulinaemia in insulin resistant horses may be associated with both increased insulin secretion and decreased insulin clearance. Potential relevance: Both C‐peptide and insulin concentrations should be measured to assess pancreatic secretion and insulin clearance in horses.