Effects of hypercalcemia on serum concentrations of magnesium, potassium, and phosphate and urinary excretion of electrolytes in horses

Assessment of calcium, phosphorus, magnesium, vitamin D and PTH levels in sera of lame horses

BACKGROUND

Minerals play vital roles in physiologic processes. Calcium, phosphorus and magnesium are common minerals. Secretion, absorption and homeostasis of these minerals are affected by associations between the active vitamin D and parathyroid hormone (PTH).

OBJECTIVE

The aim of this study was to assess concentrations of vitamin D, PTH and minerals, such as calcium, phosphorus and magnesium in horse sera, as well as associations of these values with lameness in horses. In the references, the reasons for lameness can be deficiency and imbalance of minerals, and clinical observations also confirm this and there is still not enough information regarding the relationship between mineral imbalance and lameness of horses. The prominent forms of lameness include navicular syndrome, back pain, splints, ring bone, side bone, non-infectious arthritis and bucked shins. Deficiency and inadequacy of calcium, phosphorous and magnesium have been regarded as predisposing and aggravating factors of the aforementioned diseases.

MATERIALS AND METHODS

This cross-sectional study was carried out on 60 horses, including 30 lame and 30 healthy adult horses, summer to fall 2021. Levels of calcium, phosphorus, magnesium, vitamin D and PTH were assessed in sera using automatic analyser, atomic absorption spectroscopy and commercially available kits.

RESULTS

The average level of calcium was higher healthy horses than lame horses in the two seasons (p < 0.001). The average level of inorganic phosphorus in horses was higher in summer than autumn (p < 0.001). The mean magnesium concentration in healthy horses was greater than lame horses in the two seasons (p < 0.01). In this study, the mean PTH concentration in healthy horses was lower in fall than summer (p < 0.05).

CONCLUSION

The low average levels of calcium and magnesium in lame horses in the two seasons indicate critical roles of calcium and magnesium in the normal function of the horse musculoskeletal system as well as prevention of lameness.

Effects of calcium supplementation to resuscitation fluids in endurance horses: A randomized, blinded, clinical trial

BACKGROUND

The addition of calcium to resuscitation fluids is a common practice in horses, but studies evaluating the effects of calcium supplementation are limited. In healthy horses, decreases in heart rate and changes in serum electrolyte concentrations have been reported.

HYPOTHESIS

Calcium gluconate administration at a rate of 0.4 mg/kg/min to eliminated endurance horses with metabolic problems will affect heart rate, gastrointestinal sounds, and serum electrolyte concentrations.

ANIMALS

Endurance horses eliminated from the Tevis Cup 100-mile (160 km) endurance ride for metabolic problems and requiring IV fluid therapy were eligible.

METHODS

Sixteen horses were randomly assigned to receive 0.4 mg/kg/min of calcium (23% calcium gluconate solution) over 1 hour diluted in 10 L of a non-calcium containing isotonic crystalloid (CAL group) or 10 L of a non-calcium containing isotonic crystalloid (CON group). Staff members administering the fluids were blinded to treatment group. Blood samples were collected and physical examinations performed before and after treatment. Heart rates were recorded every 15 min during fluid administration. Data were compared using 2-way analysis of variance (ANOVA) with repeated measures for continuous variables and Fisher's exact test for categorical variables.

RESULTS

Calcium was associated with lower heart rates 45 min after starting the infusion (P = .002). Gastrointestinal sounds were less likely to improve in the calcium group compared with the control group (P = .005). An increase in plasma phosphorus concentration (P = .03) was associated with calcium administration.

CONCLUSIONS

Intravenous calcium supplementation to endurance horses eliminated from competition after development of metabolic problems may decrease heart rate but impairs improvement in gastrointestinal sounds.

Plasma-Ionized Magnesium in Hospitalized Horses with Gastrointestinal Disorders and Systemic Inflammatory Response Syndrome

Simple Summary

Gastrointestinal diseases are the most prevalent diseases in hospitalized horses. One of the predisposing factors of decreased intestinal motility in horses with colic could be low plasma calcium concentration and related magnesium imbalances. Magnesium and calcium disturbances can predispose to decreased intestinal motility in horses with colic after abdominal surgery. Plasma ionized magnesium concentrations were measured in hospitalized horses with different types of gastrointestinal disorders (i.e., colic), horses with non-gastrointestinal diseases, horses with systemic inflammatory conditions and control horses; our results allowed us to conclude that hypomagnesemia was more prevalent in horses with obstructive gastrointestinal lesions. Surprisingly, no association was found with systemic inflammatory conditions nor with mortality. These valuable results suggest to us that magnesium concentrations in horses presenting obstructive colic should be monitored. Further research is needed to evaluate the effects of intravenous magnesium supplementation in horses with gastrointestinal diseases.

Abstract

Magnesium disorders in horses with gastrointestinal disorders or systemic inflammatory response syndrome (SIRS) are scarcely characterized. The purpose of the study was to explore the association of magnesium disorders with diagnosis, SIRS and mortality in horses admitted to a referral equine hospital. In total, 75 sick horses were included in an observational prospective study and classified as: obstructive (n = 17), inflammatory (n = 10) and ischemic gastrointestinal disorders (n = 12), and other non-gastrointestinal systemic disorders (n = 36). All sick horses were also divided according to the presence (n = 26) or absence of SIRS, and survival to discharge from hospital (survivors (n = 61) and non-survivors (n = 14). In addition, 26 horses were included as controls. On admission, mean (iMg) (95% confidence interval (CI)) in the SIRS group (0.47 (0.43–0.50 mmol/L)) was within the normal range (0.4–0.6 mmol/L). The obstructive group had lower (iMg) compared to the control group (0.44 (0.38–0.51 mmol/L) vs. 0.56 (0.50–0.61 mmol/L); p = 0.001). In total, 8 out of 17 (47%) horses with obstructive lesions presented with hypomagnesemia compared to controls (4% (1/26)) (p = 0.001). In conclusion, hypomagnesemia was more prevalent on admission in horses in the obstructive group, and to a lesser extent, in the inflammatory and ischemic groups. In contrast to human ICU patients, the proportion of hospitalized horses with hypomagnesemia was not associated with mortality.

Metabolic Disorders Associated with Renal Disease in Horses

This article overviews metabolic disorders associated with renal disease. Included is a discussion of the pathophysiology, clinical signs, and treatment of hyperchloremic metabolic acidosis associated with renal tubular acidosis. Conditions affecting the central nervous system including uremic encephalopathy and hyponatremic encephalopathy secondary to renal disease are presented. Finally, a discussion of the unique features of calcium and phosphorus homeostasis in horses is provided with special emphasis on a recently described syndrome of calcinosis and calciphylaxis of unknown etiology.

Effects of intravenous magnesium sulfate on serum calcium-regulating hormones and plasma and urinary electrolytes in healthy horses

Intravenous magnesium sulfate (MgSO₄) is used in equine practice to treat hypomagnesemia, dysrhythmias, neurological disorders, and calcium dysregulation. MgSO₄ is also used as a calming agent in equestrian events. Hypercalcemia affects calcium-regulating hormones, as well as plasma and urinary electrolytes; however, the effect of hypermagnesemia on these variables is unknown. The goal of this study was to investigate the effect of hypermagnesemia on blood parathyroid hormone (PTH), calcitonin (CT), ionized calcium (Ca²⁺), ionized magnesium (Mg²⁺), sodium (Na⁺), potassium (K⁺), chloride (Cl^-) and their urinary fractional excretion (F) after intravenous administration of MgSO₄ in healthy horses. Twelve healthy female horses of 4–18 years of age and 432–600 kg of body weight received a single intravenous dose of MgSO₄ (60 mg/kg) over 5 minutes, and blood and urine samples were collected at different time points over 360 minutes. Plasma Mg²⁺ concentrations increased 3.7-fold over baseline values at 5 minutes and remained elevated for 120 minutes (P < 0.05), Ca²⁺ concentrations decreased from 30–60 minutes (P < 0.05), but Na⁺, K⁺ and Cl^- concentrations did not change. Serum PTH concentrations dropped initially to rebound and remain elevated from 30 to 60 minutes, while CT concentrations increased at 5 minutes to return to baseline by 10 minutes (P < 0.05). The FMg, FCa, FNa, FK, and FCl increased, while urine osmolality decreased from 30–60 minutes compared baseline (P < 0.05). Short-term experimental hypermagnesemia alters calcium-regulating hormones (PTH, CT), reduces plasma Ca²⁺ concentrations, and increases the urinary excretion of Mg²⁺, Ca²⁺, K⁺, Na⁺ and Cl^- in healthy horses. This information has clinical implications for the short-term effects of hypermagnesemia on calcium-regulation, electrolytes, and neuromuscular activity, in particular with increasing use of Mg salts to treat horses with various acute and chronic conditions as well as a calming agent in equestrian events.

Rickets in a Thoroughbred-cross foal: case report and review of the literature

Rickets is a metabolic bone disease associated with failure of endochondral ossification and impaired osteoid mineralization in growing animals. As a consequence, affected individuals can develop gross and microscopic bone malformations. The most common causes of rickets in domestic species include vitamin D and phosphorus deficiency. Rickets has been described in multiple species; however, comprehensive postmortem characterizations with confirmatory histopathology in equids have not been published. A 6-mo-old, Thoroughbred-cross foal was diagnosed with rickets based on gross autopsy findings and microscopic examination of the ribs and long bones. Grossly, all costochondral junctions of the ribs were enlarged with a "rachitic rosary" appearance, and there were multiple fracture calluses in the rib bodies. Epiphyses and metaphyses of the long bones appeared widened on sagittal section, and their physes were irregularly thickened. Histologically, there were poorly organized columns of hypertrophic chondrocytes within the physes of affected bones, islands of chondrocytes embedded within the primary and secondary spongiosa, and faintly eosinophilic seams of poorly mineralized osteoid within the bone trabeculae. Areas of focally increased osteoclastic activity were observed in some of the sections, perhaps pointing to a more complex metabolic bone disease in a growing animal. Low serum concentrations of calcium and 25-hydroxyvitamin D were detected in an antemortem sample. The pathogenesis of these imbalances was not definitively established, but lack of sunlight exposure, low concentration of vitamin D precursors in the diet (perhaps secondary to malnutrition), or both, were suspected; a genetic basis cannot be ruled out.

Vitamin D Metabolism and Profiling in Veterinary Species

The demand for vitamin D analysis in veterinary species is increasing with the growing knowledge of the extra-skeletal role vitamin D plays in health and disease. The circulating 25-hydroxyvitamin-D (25(OH)D) metabolite is used to assess vitamin D status, and the benefits of analysing other metabolites in the complex vitamin D pathway are being discovered in humans. Profiling of the vitamin D pathway by liquid chromatography tandem mass spectrometry (LC-MS/MS) facilitates simultaneous analysis of multiple metabolites in a single sample and over wide dynamic ranges, and this method is now considered the gold-standard for quantifying vitamin D metabolites. However, very few studies report using LC-MS/MS for the analysis of vitamin D metabolites in veterinary species. Given the complexity of the vitamin D pathway and the similarities in the roles of vitamin D in health and disease between humans and companion animals, there is a clear need to establish a comprehensive, reliable method for veterinary analysis that is comparable to that used in human clinical practice. In this review, we highlight the differences in vitamin D metabolism between veterinary species and the benefits of measuring vitamin D metabolites beyond 25(OH)D. Finally, we discuss the analytical challenges in profiling vitamin D in veterinary species with a focus on LC-MS/MS methods.

Pharmacokinetics of magnesium and its effects on clinical variables following experimentally induced hypermagnesemia

The objectives of this study were to describe pharmacokinetic and pharmacodynamic changes as a result of a single intravenous administration of magnesium sulfate (MgSO₄ ) to healthy horses. MgSO₄ is a magnesium salt that has been used to calm horses in equestrian competition and is difficult to regulate because magnesium is an essential constituent of all mammals. Six healthy adult female horses were administered a single intravenous dose of MgSO₄ at 60 mg/kg of body weight over 5 min. Blood, urine, and cerebrospinal fluid (CSF) samples were collected, and cardiovascular parameters were monitored and echocardiograms performed at predetermined times. Noncompartmental pharmacokinetic analysis was applied to plasma concentrations of ionized magnesium (Mg²⁺ ). Objective data were analyzed using the Wilcoxon rank-sum test with p < .05 used as a determination for significance. Plasma concentrations of Mg²⁺ increased nearly fivefold, ionized calcium (Ca²⁺ ) decreased by nearly 10%, and the Ca²⁺ to Mg²⁺ ratio declined more than 3.5-fold and remained different than baseline until 24 hr (p < .05). Significant changes were seen with urinary fractional excretion of electrolytes, cardiovascular parameters, and echocardiographic measurements. No changes were detected in CSF electrolyte concentrations. The decrease in Ca²⁺ result of hypermagnesemia supports the interaction between these cations. Alterations detected in plasma electrolyte concentrations and urinary fractional excretion of electrolytes may serve as biomarkers for regulatory control for the nefarious administration of MgSO₄ .

Effects of Hypotonic and Isotonic Enteral Electrolyte Solutions Administered in Continuous Flow in Weaned Foals

The effects of fluid therapy with maintenance enteral electrolytic solutions administered by nasogastric route in continuous flow have not previously been studied in weaned foals. This study primary goal was to compare the effects of two maintenance enteral electrolytic solutions administered by nasogastric route in continuous flow on the hydro electrolytic balance in weaned foals. This paper was a controlled trial in a cross-over design (6 × 2) performed in six foals with a mean age of 7.3 ± 1.4 months; each animal received two treatments, IsoES and HypoES, with an interval of 7 days between treatments. After 12 h of fasting, the animals were treated with enteral electrolyte solutions administered via nasogastric route in continuous flow in a volume of 15 mL/kg/h for 12 h. The evaluations were performed at T-12h (the beginning of the fasting), T0h (end of fasting and beginning of fluid therapy), T4h (4 h of fluid therapy), T8h (8 h of fluid therapy), T12h (end of fluid therapy), and T24h (12 h after the end of fluid therapy). Twelve hours of fasting resulted in a reduction (P < 0.05) in body weight, abdominal circumference, whereas serum sodium, SID and enophthalmos increased. Twelve hours of fluid therapy normalized these parameters and promoted increased urinary volume and decreased urinary density without causing electrolyte imbalances. Both enteral electrolytic solutions were effective in reestablishing clinical and laboratorial variables without causing electrolyte imbalances.

Intravenous infusion of magnesium sulfate and its effect on horses with trigeminal-mediated headshaking

Background

Trigeminal‐mediated headshaking results from low‐threshold firing of the trigeminal nerve resulting in apparent facial pain. Magnesium may have neuroprotective effects on nerve firing that potentially dampen signs of neuropathic pain. This hypothesis has not been investigated in horses with trigeminal‐mediated headshaking.

Objective

To investigate head‐shaking behavior in affected horses after IV magnesium sulfate infusion.

Animals

Six geldings with trigeminal‐mediated headshaking.

Methods

Prospective randomized crossover study. Horses were controlled for diet and infused IV with 5% dextrose solution (DS; control solution at 2 mL/kg body weight [BW]) and MgSO₄ 50% solution (MSS at 40 mg/kg BW). Head‐shaking behavior was recorded at times T0 (baseline, before infusion) and T15, T30, T60, and T120 minutes post‐infusion. Venous blood variables such as pH, HCO₃⁻, standard base excess (SBE), Na⁺, Cl⁻, K⁺, Ca²⁺, Mg²⁺, total magnesium (tMg), glucose, and lactate were measured; strong ion difference (SID) and anion gap (AG) were calculated for each time point.

Results

Blood variables including pH, Na⁺, Cl⁻, K⁺, SID, AG, lactate, Ca²⁺, tMg, and Mg²⁺ had significant changes with MSS as compared to DS treatment. Glucose, SBE, and HCO₃⁻ did not have significant changes. A 29% reduction in head‐shaking rate occurred after MSS treatment but no change occurred after DS treatment.

Conclusions and Clinical Importance

Administration of MSS IV increased plasma total and ionized magnesium concentrations and significantly decreased head‐shaking behavior in horses with trigeminal‐mediated headshaking.

Persistent Hypercalcemia and Hyperparathyroidism in a Horse

A 27-year-old, American Quarter Horse gelding was evaluated for anorexia, lethargy, a swelling on the right, cranial aspect of the neck, and signs of esophageal obstruction. Serum biochemical analyses revealed hypophosphatemia, total and ionized hypercalcemia, and hemoconcentration. Sonographic examination of the neck revealed a 1.7 cm diameter mass within the right lobe of the thyroid. The serum concentration of intact parathyroid hormone (iPTH) was increased. The right lobe of the thyroid was excised with the horse sedated. The mass within that lobe was determined, by histological examination, to be a parathyroid adenoma. Despite excision of the mass, serial blood analyses revealed persistent hypercalcemia, hypophosphatemia, and increased iPTH. Anorexia and lethargy resolved, and follow-up communication with the owner and referring veterinarian one year later indicated that the horse was clinically stable.

A case report: Giant cystic parathyroid adenoma presenting with parathyroid crisis after Vitamin D replacement

BACKGROUND

Parathyroid adenoma with cystic degeneration is a rare cause of primary hyperparathyroidism. The clinical and biochemical presentation may mimic parathyroid carcinoma.

CASE PRESENTATION

We report the case of a 55 year old lady, who had longstanding history of depression and acid peptic disease. Serum calcium eight months prior to presentation was slightly high, but she was never worked up. She was found to be Vitamin D deficient while being investigated for generalized body aches. A month after she was replaced with Vitamin D, she presented to us with parathyroid crisis. Her corrected serum calcium was 23.0 mg/dL. She had severe gastrointestinal symptoms and acute kidney injury. She had unexplained consistent hypokalemia until surgery. Neck ultrasound and CT scan revealed giant parathyroid cyst extending into the mediastinum. After initial medical management for parathyroid crisis, parathyroid cystic adenoma was surgically excised. Her serum calcium, intact parathyroid hormone, creatinine and potassium levels normalized after surgery.

CONCLUSION

This case of parathyroid crisis, with very high serum calcium and parathyroid hormone levels, is a rare presentation of parathyroid adenoma with cystic degeneration. This case also highlights that Vitamin D replacement may unmask subclinical hyperparathyroidism. Consistent hypokalemia until surgery merits research into its association with hypercalcemia.

Miscellaneous neurologic or neuromuscular disorders in horses

NMD is an important cause of morbidity in horses. Signs of dysfunction could be variable depending on the specific area affected. NM disease can go unrecognized if a thorough evaluation is not performed in diseased horses. Electrodiagnostic testing is an area that has the potential to document and improve our understanding of NM disease yet is uncommonly performed. Keeping an open and observant mind will enhance our ability to search and find answers.

Magnesium disorders in horses

Magnesium (Mg) is an essential macroelement that is required for cellular energy-dependent reactions involving adenosine triphosphate and for the regulation of calcium channel function. Subclinical hypomagnesemia is common in critically ill humans and animals and increases the severity of the systemic inflammatory response syndrome; worsens the systemic response to endotoxins; and can lead to ileus, cardiac arrhythmias, refractory hypokalemia, and hypocalcemia. This article discusses the clinical signs, consequences, and treatment of hypomagnesemia in horses and describes the association of Mg and endotoxemia, insulin resistance, and brain injury.

Toward the optimal clinical use of the fraction excretion of solutes in oliguric azotemia

While the fractional excretion of solutes have long been considered excellent research tools to investigate tubular physiology, their clinical use has become common over the last 40 years in the diagnoses of many disorders; however, none have reached the clinical utility of the fractional excretion of sodium in the ability to distinguish pre-renal azotemia from acute tubular necrosis. Nevertheless, there are many drugs and medical conditions that interfere with that utility and recently other solutes, including urea, uric acid and lithium, have been recently investigated to improve the diagnostic ability in clinical situations where the fractional excretion of sodium is known to be unreliable. We review the tubular physiology of these solutes and show how the differences in tubular physiology might be exploited to develop a strategy for their optimal clinical use.

Rapid calcitonin response to experimental hypercalcemia in healthy horses

Calcium has important physiological functions, and disorders of calcium homeostasis are frequent in horses. We have made important progress understanding equine calcium homeostasis; however, limited information on equine calcitonin (CT) is available, in part because of the lack of validated CT assays. To determine the CT response to high ionized calcium (Ca(2+)) concentrations in healthy horses, we induced hypercalcemia in 10 healthy horses using a calcium gluconate 23% solution (5mg/kg; 120 mL/500 kg horse) infused over 4 min. Four horses were infused with 120 mL of 0.9% NaCl and used as controls. We validated a human-specific CT radioimmunoassay for use in horses. Serum Ca(2+) concentrations increased from 6.2+/-0.3mg/dL to 9.9+/-0.5mg/dL (4 min; P<0.01). Serum CT increased from 16.7+/-8.0 pg/mL to 87.1+/-55.8 pg/mL at 2 min, and 102.5+/-51.1 pg/mL at 4 min (P<0.01). Serum CT returned to baseline by 20 min, whereas serum Ca(2+) returned to baseline by 40 min. Of interest, CT concentrations returned to baseline despite hypercalcemia, suggesting thyroid gland C-cell CT depletion. Resting CT values higher than 40 pg/mL were considered abnormally elevated. No significant changes in serum Ca(2+) or CT concentrations were found in control horses. The coefficients of variation for the CT radioimmunoassay were lower than 11.9%. We conclude that the equine thyroid gland C-cell responds quickly to changes in extracellular Ca(2+) concentrations by secreting large quantities of CT into the systemic circulation, indicating that CT is important in equine calcium homeostasis. The human CT radioimmunoassay can be used to measure changes in equine CT.

Urinalysis in three species of captive rhinoceros (Rhinoceros unicornis, Dicerorhinus sumatrensis, and Diceros bicornis)

This study reports urinalysis values for three species of captive rhinoceros (Rhinoceros unicornis, Dicerorhinus sumatrensis, and Diceros bicornis) and evaluates individual and species differences. Repeated urinalysis was conducted on 11 individuals to establish normal reference ranges. Although no individual or species differences existed in urinary values for pH, all species differed in specific gravity. Rhinoceros urine demonstrated many physical and chemical properties similar to that of the horse, but reliability of this comparison was limited. Urinary pH in the rhinoceros was within range of that established for the horse and other large herbivores. However, all rhinoceros species exhibited urinary specific gravities below the lower limit of the normal equine reference range. Comparative urinalysis using an outside laboratory source confirmed the results of this study and illustrated the value of conducting in-house analysis. These results are the first data available on reference ranges for urine parameters in the greater one-horned, Sumatran, and African black rhinoceros and provide a useful diagnostic tool for the veterinary care of individuals in captivity.

Fractional excretion tests: a critical review of methods and applications in domestic animals

The fractional excretion (FE) of a constituent by the kidney is the fraction of the amount filtered by the glomerulus, which is excreted into urine. It is mostly determined for electrolytes, and is expressed as the ratio of the clearance of a given electrolyte to creatinine clearance. The main physiologic factors affecting FE variation are species, age, and the alimentary supply of electrolytes. The value of FE tests in the diagnosis of kidney disease is limited, except in canine Fanconi's syndrome. FEs of many constituents often are increased in chronic kidney disease, but their diagnostic value is no greater than that of plasma creatinine concentration. FEs also are altered in nonrenal diseases such as diabetes mellitus and rhabdomyolysis, and during treatment with xylazine, rehydration fluids, and diuretics. FEs, especially of calcium, phosphates, and magnesium, are useful in clinical nutrition to assess mineral balance. FE is difficult to measure, so its use should be limited to nutritional investigations and nephrology research.