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paralysis or somnolence develops, typically within 72 hours of parturition. The condition most often develops in high-yield cows. If treatment is not initiated, the disease can be fatal. 6,7 In mammals, calcium plays an integral role in many physiologic

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in American Journal of Veterinary Research

Abstract

Objective

To determine effects of exercise on blood ionized calcium (Ca2+) and plasma parathyroid hormone (PTH) concentrations in horses and to compare the effects of exercise-induced and EDTA-induced hypocalcemia on PTH secretion.

Animals

17 horses entered in a show jumping competition and 5 horses given EDTA.

Procedure

Blood Ca2+ and plasma PTH concentrations were measured before and after exercise in the 17 horses entered in the jumping competition. In the other 5 horses, concentrations were measured during infusion of EDTA IV.

Results

Exercise resulted in a significant decrease in blood Ca2+ concentration and a significant increase in plasma PTH concentration, and blood Ca2+ concentration was correlated with plasma PTH concentration. Administration of EDTA resulted in hypocalcemia and an increase in PTH concentration. For the same decrease in Ca2+ concentration, magnitude of the exercise-induced increase in PTH concentration was similar to magnitude of the EDTA-induced increase.

Conclusions and Clinical Relevance

Results suggest that the increase in plasma PTH concentration in horses after exercise is secondary to hypocalcemia and that the increase in PTH concentration seems to be commensurate with the decrease in Ca2+ concentration. (Am J Vet Res 1998;59:1605-1607)

Free access
in American Journal of Veterinary Research

SUMMARY

Blood ionized calcium (Ca2+) and pH; plasma lactate concentrations; and total protein, total calcium (CaT), albumin, and phosphorus concentrations in serum were determined in 40 healthy horses before (T1), at the finish line (T2), and 10 minutes after the finish (T3) of the cross-country phase of a 3-day-event competition. Mean (± sem) Ca2+ concentrations decreased from 6.22 ± 0.04 mg/dl at T1 to 5.04 ± 0.07 mg/dl at T2 (P ≤ 0.05). This decrease was accompanied by a nonsignificant increase in CaT between T1 and T2. The mean (± sem) percent ionization of calcium decreased significantly (P ≤ 0.05), from 50.9 ± 2.75% at T1 to 40.3 ± 3.58% at T2. Significant increases in mean albumin, total protein, phosphorus, and lactate concentrations and a significant decrease in mean pH were observed at T2 (P ≤ 0.05). At T3, mean Ca2+ and percent ionization had increased, but remained significantly less than resting values. Mean CaT was significantly decreased at T3, compared with values at T1 and T2. Correlation of mean Ca2+ concentration with all other measured variables at each time was evaluated; correlation coefficients between mean Ca2+ and all other variables were low (r 2 ≤ 0.38), indicating low biological significance.

Free access
in American Journal of Veterinary Research

SUMMARY

Plasma and milk concentrations of parathyroid hormone-related protein (PTHrP) at various stages of pregnancy and lactation were determined in thirtynine 3- to 16-year-old Brown Swiss and Red Holstein × Simmental dairy cows originating from 4 herds. Eighteen of the cows were separated into 2 groups: low-parity (lp, n = 8) cows if they were in their first or second pregnancy and high-parity (hp, n = 10) cows if they were in their third or greater pregnancy. Blood samples were collected from each cow on 1 occasion, 15 to 5 days before calving, and blood and milk samples were collected daily during 6 days after calving. Serum total and ionized calcium (Catot and Ca2+, respectively) and milk Catot concentrations were also quantified.

A transient postpartum decrease of serum Catot and Ca2+ concentrations was observed, whereas milk Catot concentration was constant. Plasma concentration of PTHrP was detected in 11 of 21 cows by use of an immunoradiometric assay (range, 0.45 to 1.82 pmol/L). Daily mean (± sd) colostrum and milk PTHrP concentrations ranged from 3.25 (± 3.23) to 4.69 (± 1.36) nmol/L in lp cows and 2.74 (± 0.5) to 5.95 (± 0.33) nmol/L in hp cows. In all cows of the hp group and most cows of the lp group, milk PTHrP concentration was highest in the day-1 sample. Milk PTHrP concentration correlated positively with milk Catot concentration in hp cows (r = 0.5959, P < 0.0001). In contrast, there was a negative relation between milk PTHrP and milk Catot concentrations in lp cows (r = −0.3285, P < 0.02). Milk PTHrP concentration was not correlated with serum Ca2+ concentration at postpartum days 5 and 6, when serum Catot and Ca2+ concentrations had returned to prepartum values. Because correlation did not exist between the lowest serum Ca2+ values and milk PTHrP concentration of the corresponding day, milk PTHrP concentration most likely is not a major determinant of Ca transport into milk and the PTHrP released into the blood stream is most likely not a major determinant of the endocrine regulation of serum Catot and Ca2+.

Thus, although it is involved, PTHrP is not a major factor in the integrative endocrine, paracrine, and autocrine regulation of Ca homeostasis in lactating cows. It is hypothesized that Ca may be actively transported from blood into milk with a process modulated by PTHrP. These data suggest that PTHrP produced by the mammary gland is most likely not involved in the pathogenesis of parturient paresis (milk fever) in dairy cows.

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in American Journal of Veterinary Research

Summary

The ability of ectopic parathyroid tissue to support calcium homeostasis was evaluated by measuring serum concentrations of calcium, phosphorus, albumin, magnesium, and parathyroid hormone before and for 12 weeks after bilateral thyroparathyroidectomy in 14 cats. During the immediate postoperative period, significant decrease was observed in serum calcium, magnesium, and parathyroid hormone (pth) concentrations. Serum pth concentration remained subnormal and did not significantly increase during the 12-week observation period. Despite persistent hypoparathyroidism, serum calcium and magnesium concentrations gradually increased. Ectopic parathyroid tissue is not capable of maintaining normal serum calcium concentration immediately after thyroparathyroidectomy. Serum calcium concentration gradually normalizes after thyroparathyroidectomy, apparently by means of a pth-independent mechanism.

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in American Journal of Veterinary Research

nutritional disorders such as calcium deficiencies and subsequent metabolic bone diseases are rare in wild chelonians. Although a considerable amount of evidence-based information has been obtained on reptile physiology-biology 9–11 and management, 12

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in American Journal of Veterinary Research

including calcium, potassium, magnesium, and phosphate. 9 Severe decreases in the blood concentrations of these electrolytes can cause recumbency in dairy cows. 10 Consequently, it is critical to determine whether IV administration of dextrose puts cows at

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in American Journal of Veterinary Research

of urea, creatinine, total protein, albumin, calcium, sodium, potassium, phosphorus, chloride, and iron were determined by use of a commercial kit c and clinical chemistry analyzer. d Serum AST, CK, and LDH activities were determined with a

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in American Journal of Veterinary Research

, potassium, chloride, and ionized calcium were measured by use of an automated analyzer. d Hemoglobin concentration was measured by photometric determination, e and phosphorus and albumin concentrations were measured by use of an automated analyzer. f The

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in American Journal of Veterinary Research

.20 ± 0.08 mg/dL) at 24 hours (0.65 ± 0.30 mg/dL; P < 0.001) and 7 days (0.46 ± 0.07 mg/dL; P = 0.004) after infusion. Serum calcium concentration was significantly ( P < 0.001) increased from the preinfusion value (9.80 ± 0.55 mg/dL) at 24 hours

Full access
in American Journal of Veterinary Research