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Objective: To describe the surgical technique and clinical outcome of minimally invasive parathyroidectomy for primary hyperparathyroidism (PHPT) in the dog., Animals: Fifty client-owned dogs with PHPT that underwent minimally invasive parathyroidectomy., Study Design: Retrospective cohort study., Methods: An ultrasound-guided mini lateral approach was made via a plane established between the sternocephalicus muscle and sternohyoideus muscles to expose the thyroid gland and enlarged parathyroid gland. Abnormal parathyroid glands were removed en bloc via partial thyroidectomy. The technique for bilateral disease was similar, the skin incision was made on midline and moved laterally to develop the above-mentioned plane of dissection. Age, sex, breed, bodyweight, ultrasound findings, histopathological diagnosis, surgical time, preoperative clinical signs, and clinical outcome were extracted from the records for descriptive statistics., Results: A total of 62 glands were surgically removed, including 17 hyperplastic glands (17/62, 27.4%), 34 adenomas (34/62, 54.8%), and two carcinomas (2/62, 3.2%). Hypercalcemia resolved shortly after surgery in 44 dogs (44/45, 97.8%). One dog had recurrent hypercalcemia (1/45, 2.2%), one dog had persistent hypercalcemia (1/45, 2.2%), two dogs had permanent hypocalcemia requiring life-long calcitriol supplementation (2/45, 4.4%), and one dog died from clinical hypocalcemia (1/45, 2.2%)., Conclusion: Minimally invasive parathyroidectomy was associated with a low morbidity and led to favorable outcomes in 44/45 dogs in this series., Clinical Significance: The results of this study supports the use of minimally invasive parathyroidectomy to treat PHPT in dogs., (© 2022 American College of Veterinary Surgeons.)

Objective: To describe a minimally invasive approach to the parathyroid gland for the treatment of primary hyperparathyroidism., Study Design: Surgical technique description and clinical case report., Animals: Five canine cadavers and 5 client-owned dogs with primary hyperparathyroidism., Methods: A surgical technique for minimally invasive video-assisted parathyroidectomy (MIVAP), described for humans, was adapted for dogs. With the dog in dorsal recumbency, a 15 mm incision was made on the midline, 1 finger width caudal to the cricoid cartilage of the larynx. A 5 mm 30° rigid endoscope was inserted into the peritracheal space with the aid of a blunt suction dissector, and fine elevators. The parathyroid was subsequently removed using electrocautery and blunt and sharp dissection. The technique was refined in 5 cadaver dogs to assess feasibility, and was subsequently performed in 5 clinical cases., Results: A minimally invasive approach to the parathyroid gland was possible and allowed successful removal of a parathyroid mass in 5 dogs without complication. The use of fluid ingress was trialed in 1 cadaver and not found to be helpful. The use of a blunt suction dissector greatly facilitated dissection of the peritracheal space., Conclusion: Minimally invasive video-assisted parathyroidectomy is feasible in dogs and was not associated with complications in 5 clinical cases., Clinical Significance: Minimally invasive techniques tend to reduce morbidity and are popular with pet owners. This study demonstrates that a minimally invasive technique may be considered for parathyroidectomy in dogs., (© 2022 American College of Veterinary Surgeons.)

This article provides a review with a focus on clinical updates in treating patients with surgical parathyroid or thyroid disease. Primary hyperparathyroidism is a common cause of hypercalcemia. Patients are older and often asymptomatic, and urinary stones and urinary tract infection are common. Surgical treatment is recommended with an excellent prognosis. Thyroid tumors in dogs are the most common endocrine neoplasm. Functional thyroid testing, laryngeal examinations, and regional lymphadenectomy should be considered during surgery, along with use of vessel-sealing devices to mitigate hemorrhage. Long-term outcomes for dogs with advanced disease can be reached, so surgical resection should be an option., Competing Interests: Disclosure The authors have nothing to disclose., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Objective: To investigate (1a) agreement of ultrasonographic, surgical, and histopathologic findings in the diagnosis of a neoplastic etiology underlying primary hyperparathyroidism (PHPT), (1b) the ability of ultrasonographically determined parathyroid gland size to distinguish between malignant (carcinoma) and non-malignant (hyperplasia, adenoma) pathology, and (2) variables associated with postoperative hypocalcemia in dogs undergoing surgical treatment of PHPT., Study Design: Ambidirectional cohort study., Animals: Forty-seven client owned dogs with PHPT (34 retrospective; 13 prospective)., Methods: Data were extracted from medical records. Method agreements were explored using Cohen's Kappa statistic. A receiver operating characteristic curve (ROC) was used to determine a cut-off separating parathyroid pathologies. Univariable and multivariable models assessed associations between postoperative hypocalcemia and potential risk factors., Results: Agreement of ultrasound and surgery for number and side of affected glands was 31/47 (65.9%) and 34/47 (72.3%), respectively. In 37/47 (78.7%) cases, parathyroid tissue was correctly assessed as pathologic by the surgeon. An ultrasonographic cut-off of ≥8.0 mm (ROC AUC = 0.82) best distinguished malignant from benign pathologies. Dogs with a preoperative serum ionized calcium (iCa) concentration ≥1.75 mEq/L had 7.5 times greater odds of becoming hypocalcemic postoperatively., Conclusion: A fair agreement existed between ultrasonographic and surgical findings in dogs with PHPT. A parathyroid mass ≥8.0 mm on ultrasonographic examination was suggestive of malignancy, while dogs with a preoperative serum iCa concentration ≥1.75 mEq/L were at increased risk for postoperative hypocalcemia in this study., Clinical Significance: This study supports the use of bilateral cervical surgical exploration to identify abnormal parathyroid glands for the treatment of PHPT., (© 2021 The Authors. Veterinary Surgery published by Wiley Periodicals LLC on behalf of American College of Veterinary Surgeons.)

Background: Primary hyperparathyroidism (PHPT) is an uncommon condition in dogs, for which there is a documented genetic predisposition in Keeshonden and sporadic cases in other breeds. Secondary literature reports a 10 per cent prevalence for recurrence in patients successfully treated by surgical parathyroidectomy, however there is no published primary literature available on which to base this assertion. This study sought to document prevalence of recurrence within Keeshonden and non-Keeshonden breeds. The authors hypothesised that Keeshonden would have a higher rate of recurrence due to the genetic predisposition for the disease, as compared with sporadic cases in other breeds, and that Keeshonden might have an earlier age of detection of disease., Methods: A retrospective review of medical records was undertaken to assess the prevalence of recurrence, the length of time after diagnosis that the recurrence occurred, and the age of initial diagnosis in both Keeshonden and non-Keeshonden breeds., Results: The study found that Keeshonden were significantly more likely to develop recurrence (6/12, 50 per cent) than non-Keeshonden dogs (1/15, 7 per cent) (P=0.024), and were significantly younger (median 108 v 126 months, P=0.043) at initial disease detection. Recurrence in Keeshonden occurred at median 35 months after treatment., Conclusion: This suggests all dogs treated by curative parathyroidectomy for PHPT should be monitored lifelong for recurrence of disease, and that this is particularly pertinent in the Keeshond population. Earlier screening of younger, apparently healthy Keeshonden may also be advisable., Competing Interests: Competing interests: None declared., (© British Veterinary Association 2020. No commercial re-use. See rights and permissions. Published by BMJ.)

Objective: To report perioperative characteristics, complications, histopathologic diagnosis and outcome in cats undergoing surgical treatment for primary hyperparathyroidism (PHPT)., Study Design: Multi-institutional, retrospective case series., Animals: Thirty-two client-owned cats., Methods: Medical records of cats treated with surgical removal of 1 or more parathyroid gland(s) with confirmed histopathologic evaluation were reviewed. Cats were divided into preoperative ionized calcium (iCa) groups corresponding to the 33rd, 67th, and 100th percentiles of the preoperative iCa results of the study population. Follow-up consisted of phone conversation with owners or primary veterinarian., Results: Ionized calcium was above reference range in all cats (median 1.8 mmol/L [interquartile range, 1.5-1.9]). Abnormal tissue was excised after cervical exploration in all cats. The most common histopathologic diagnoses were parathyroid adenoma in 20 of 32 (62.5%) cats and parathyroid carcinoma in 7 of 32 (21.9%) cats. At discharge, 6 of 32 (18.8%) cats had hypercalcemia, 5 of 32 (15.6%) had hypocalcemia, and 21 of 32 (65.6%) were normocalcemic. Preoperative iCa did not correlate with postoperative iCa. The median follow-up time was 332 days (range, 7-3156). Overall median survival time was 1109 days (95% CI, 856-1332). Survival time was not associated with preoperative iCa group, hypocalcemia at discharge, hypercalcemia at discharge, or diagnosis of carcinoma., Conclusion: In this cohort of cats, parathyroid adenoma was the most common cause of PHPT, and surgical treatment resulted in very good median survival time. Preoperative iCa was not predictive of postoperative hypocalcemia., Clinical Significance: Surgical parathyroidectomy for treatment of PHPT in cats provides a favorable prognosis., (© 2019 The American College of Veterinary Surgeons.)

Background: Prophylactic administration of calcitriol has been suggested to mitigate the risk of hypocalcemia after parathyroidectomy. The effect of calcitriol on postoperative serum ionized calcium concentrations has not been evaluated in dogs after parathyroidectomy., Hypothesis/objectives: To determine the effect of prophylactic calcitriol administration on postoperative serum ionized calcium (iCa) concentrations in dogs with primary hyperthyroidism (PHPTH) treated by parathyroidectomy., Animals: Seventy-eight dogs with primary hyperparathyroidism treated surgically., Methods: Multi-institutional retrospective case study. Medical records from 2005 to 2015 were evaluated. Dogs were included if they had a diagnosis of PHPTH and had surgery to remove parathyroid tissue. Serum iCa concentrations were monitored for a minimum of 2 days postoperatively. Two study groups were evaluated: calcitriol administration and no calcitriol administration., Results: Serial postoperative iCa concentrations measured at 12-hour time intervals for 2 days postoperatively were positively associated with preoperative iCa concentrations. This association was evident at each time interval, and the effect of preoperative iCa concentrations on postoperative iCa concentrations decreased as time elapsed (12 hours, P < 0.0001; 24 hours, P < 0.0001; 36 hours, P < 0.04; and 48 hours, P = 0.01). Prophylactic calcitriol administration was not found to be significantly associated with postoperative iCa concentrations or its rate of decrease after parathyroidectomy., Conclusion and Clinical Importance: We found no protective value in administering calcitriol prophylactically to prevent hypocalcemia in the immediate postoperative period (48 hours) after parathyroidectomy. Preoperative iCa concentrations had a significant positive association with postoperative iCa concentrations throughout the monitoring period., (Copyright © 2017 The Authors. Journal of Veterinary Internal Medicine published by Wiley Periodicals, Inc. on behalf of the American College of Veterinary Internal Medicine.)

Background: Development of hypocalcemia after treatment of hyperparathyroidism results in increased costs and risk of poorer outcomes. Previous studies have shown conflicting data about predictors of hypocalcemia after these procedures., Hypothesis/objectives: The objective of this study was to investigate whether ionized calcium (iCa) concentrations before treatment are predictive of hypocalcemia or its clinical signs after surgical removal or heat ablation in dogs with primary hyperparathyroidism., Animals: Fifty-four dogs with primary hyperparathyroidism (29 female, 25 male; 49 retrospective, 5 prospective)., Methods: Dogs were enrolled if they met the inclusion criteria: persistent hypercalcemia (iCa >1.41 mmol/L) due to primary hyperparathyroidism and absence of preemptive calcitriol treatment. All dogs were treated with parathyroidectomy (n = 37) or percutaneous ultrasound-guided heat ablation (n = 17). After treatment, iCa was monitored twice daily until plateau or intervention., Results: There was a moderate correlation between before-treatment hypercalcemia and after-treatment hypocalcemia. The prospective study was terminated due to ethical concerns given findings in the retrospective section. All dogs were placed into groups according to their pretreatment iCa: 1.46-1.61 mmol/L, 1.62-1.71 mmol/L, iCa 1.72-1.81 mmol/L, or >1.81 mmol/L. After treatment, the mean lowest iCa for each group, respectively, was 1.19, 1.18, 1.13, and 1.01 mmol/L. There was a significant association between higher group and proportion of dogs with iCa <1.00 mmol/L (P = .014)., Conclusions and Clinical Importance: This study demonstrates a moderate correlation between iCa concentration before treatment and hypocalcemia after treatment. Dogs with higher initial iCa concentrations should be treated to prevent rapid decline and development of clinical hypocalcemia., (Copyright © 2017 The Authors. Journal of Veterinary Internal Medicine published by Wiley Periodicals, Inc. on behalf of the American College of Veterinary Internal Medicine.)

A 13-year-old dog exhibited dramatic, radiographic osteopenia consistent with fibrous osteodystrophy secondary to primary hyperparathyroidism. Following parathyroidectomy, the dog developed severe, prolonged hypocalcemia, but was successfully treated and discharged 32 d after surgery. A variety of factors may have contributed to this dog's hypocalcemia including hypoparathyroidism and hungry bone syndrome.

Objective: To identify preoperative variables associated with postoperative hypocalcemia in dogs with primary hyperparathyroidism undergoing parathyroidectomy., Design: Retrospective case series., Animals: 62 dogs., Procedures: Medical records of dogs undergoing parathyroidectomy for treatment of primary hyperparathyroidism between January 2004 and January 2009 at 4 institutions were reviewed; data regarding various preoperative variables and postoperative serum total and ionized calcium concentrations were recorded. Preoperative ultrasonographic and surgical findings were compared regarding laterality (right, left, or bilateral) of parathyroid gland lesions. Data were analyzed via ANOVA, simple linear regression, and multiple linear regression to identify associations between preoperative variables and postoperative serum total and ionized calcium nadir concentrations., Results: Preoperative variables significantly associated with low postoperative serum total calcium nadir concentrations included old age, history of weakness, lack of gastrointestinal tract signs, high serum parathyroid hormone concentration, and low serum calcium-phosphorus concentration product value. Preoperative variables significantly associated with low postoperative serum ionized calcium nadir concentrations included sexually intact status, low body weight, high serum urea nitrogen concentration, and lack of polyuria and polydipsia in the history. Age, body weight, serum calcium-phosphorus concentration product, and serum concentrations of parathyroid hormone and urea nitrogen were included in the final multiple linear regression model for prediction of postoperative serum calcium concentrations. Ultrasonography was performed in 58 dogs; results for 44 (75.9%) dogs agreed with surgical findings regarding laterality of parathyroid gland lesions., Conclusions and Clinical Relevance: Prediction of postoperative hypocalcemia in dogs in this study with primary hyperparathyroidism that underwent parathyroidectomy was difficult and depended on multiple (history, physical examination, and clinicopathologic) factors.

Objective: To determine whether preoperative serum ionized calcium (iCa) or parathyroid hormone (PTH) concentrations help predict postoperative hypocalcemia following parathyroidectomy in dogs with primary hyperparathyroidism., Design: Retrospective case series., Animals: 17 dogs with primary hyperparathyroidism treated with parathyroidectomy., Procedures: Medical records were evaluated from years 2001 to 2009. Data evaluated included age, breed, sex, clinical signs, diagnostic tests performed, preoperative and postoperative iCa concentrations, preoperative PTH concentrations, and whether calcium supplementation was provided following surgery. Two groups were identified on the basis of whether dogs became hypocalcemic (iCa < 1.2 mmol/L) following parathyroidectomy., Results: 12 dogs developed hypocalcemia after surgery. Preoperative (within 24 hours before surgery) iCa concentrations for the hypocalcemic group (mean ± SD, 1.82 ± 0.22 mmol/L) and the nonhypocalcemic group (1.83 ± 0.29 mmol/L) were not significantly different. Calcium concentrations decreased in a linear fashion during the 24 hours following parathyroidectomy, and the slopes of the decrease over that time were not significantly different between the 2 groups. Preoperative PTH concentrations were not significantly different between the hypocalcemic and nonhypocalcemic groups., Conclusions and Clinical Relevance: Preoperative iCa and PTH concentrations were not predictive of postoperative hypocalcemia in dogs undergoing parathyroidectomy for primary hyperparathyroidism. Future studies to evaluate whether calcium supplementation should be provided on an individual basis with perhaps more emphasis on clinical signs than iCa concentrations after surgery may be warranted.

Objective: To determine (1) whether the intraoperative parathyroid hormone concentration ([PTH]) during parathyroidectomy (PTX) can be used to indicate cure in dogs with primary hyperparathyroidism and (2) the time taken for postoperative serum calcium concentration to normalise., Design: Retrospective study (2005-10) from a private referral hospital in Sydney, New South Wales, Australia., Procedure: Nine client-owned dogs underwent surgical PTX for naturally occurring primary hyperparathyroidism. [PTH] was measured from serum samples taken immediately post-induction (pre-PTX]) and at least 20 min after adenoma removal (post-PTX) for all dogs, and during parathyroid gland manipulation (intra-PTX) for six dogs. The concentration of ionised calcium (iCa) was measured at various time points postoperatively until it normalised, then stabilised or decreased below reference ranges. Statistical analysis compared the mean pre-, intra- and post-PTX [PTH] and the average rate of decline of iCa concentration postoperatively., Results: All dogs demonstrated a significant decrease from mean pre-PTX [PTH] (168.51 pg/mL) to mean post-PTX [PTH] (29.20 pg/mL). There was a significant increase in mean intra-PTX [PTH] (279.78 pg/mL). The average rate of decline of iCa concentration postoperatively to within the reference range (1.12-1.40 mmol/L) occurred after 24 h., Conclusion: Intraoperative measurements of [PTH] can be used clinically to determine cure of primary hyperparathyroidism. Parathyroid hormone increases significantly during parathyroid gland manipulation. Plasma iCa concentration returns to within the reference range on average 24 h after successful PTX. Not all dogs require vitamin D or calcium supplementation pre- or postoperatively., (© 2012 The Authors. Australian Veterinary Journal © 2012 Australian Veterinary Association.)

Objective: Retrospective evaluation of diagnosis and outcome in 20 dogs with primary hyperparathyroidism., Material and Methods: In 20 dogs primary hyperparathyroidism was diagnosed and 19 patients were treated via parathyroidectomy, 10 additionally with partial thyroidectomy. Medical records of the dogs were reviewed for signalment, clinical features, laboratory findings and results of histopathologic examination. In some cases postsurgical rehabilitation of calcium metabolism required substitution with calcium and vitamin D preparations., Results: Mean age of the dogs was 11.5 years. The most common clinical signs comprised polydipsia, polyuria, reduced activity, and stiff gait. Laboratory findings were moderate to extensive hypercalcaemia, low or low-normal serum phosphorus concentrations and normal or increased serum parathyroid hormone concentrations. None of the dogs had an elevated parathyroid hormone-related polypeptide level. Histological examination revealed 11 adenomas, six carcinomas and two glandular hyperplasias. Postsurgical management of calcium homeostasis was challenging in some cases., Conclusion: Tumours of the parathyroid gland can be easily treated by parathyroidectomy and usually have a good prognosis., Clinical Relevance: With careful interpretation of laboratory findings of a patient presenting with hypercalcaemia and ruling out other causes of hypercalcaemia diagnosis of primary hyperparathyroidism can be easily achieved and successfully treated byparathyroidectomy.

Primary hyperparathyroidism is a common cause of hypercalcemia in dogs. The diagnosis requires careful interpretation of test results, and treatment involves removal of the affected gland(s).

The medical records of 110 dogs treated for primary hyperparathyroidism were reviewed. Dogs were treated via parathyroidectomy (n=47), percutaneous ultrasound-guided ethanol ablation (n=15), or percutaneous ultrasound-guided heat ablation (n=48). Forty-five of 48 (94%) parathyroidectomies resulted in control of hypercalcemia for a median of 561 days. Thirteen of 18 (72%) ethanol ablation procedures resulted in control of hypercalcemia for a median of 540 days. Forty-four of 49 (90%) heat-ablation treatments resulted in control of hypercalcemia for a median of 581 days.

Objectives: To review the records of 29 dogs diagnosed with primary hyperparathyroidism and see if any factors correlate with renal failure., Methods: Dogs were selected retrospectively from case files from the QVSH and the QMH., Results: The majority of dogs were middle-aged and four were keeshonds. The primary presenting complaints were polyuria and polydipsia. All dogs had an elevated total and ionised plasma calcium concentration. Plasma phosphate concentrations were variable. Ultrasonography of the parathyroid gland revealed nodular enlargement which was found to correlate well with surgical findings. The majority of dogs underwent surgical parathyroidectomy. Five cases were treated by ultrasound-guided chemical ablation of the parathyroid gland, of which only two cases showed a partial response. Three dogs were euthanased within a week of presentation. Seven other dogs had renal failure diagnosed either at presentation or up to six months after parathyroidectomy. The development of renal failure was correlated with total calcium concentration but did not correlate with any other factor, including the calcium phosphate product. Thirteen treated dogs were known to be alive at the time of writing, which was six months to 3.5 years after parathyroidectomy., Clinical Significance: Primary hyperparathyroidism cases with high total calcium were more likely to develop renal failure in this group of dogs; however, the calcium phosphate product did not seem to be a useful predictor. Ultrasound-guided chemical ablation seemed to have limited advantage over surgery.

During an annual physical examination, a middle-aged adult female olive baboon (Papio anubis) in the time-mated breeding colony at the Biologic Resources Laboratory at the University of Illinois at Chicago was found to have a high serum calcium value (> 12 mg/dl). To determine the cause of the hypercalcemia, additional diagnostic tests, including thoracic and abdominal radiographs and a parathyroid panel (parathyroid hormone (PTH), ionized calcium, and parathyroid hormone-related protein (PTH-rp) assays), were performed. The radiographs did not reveal lesions suggestive of neoplasia. A parathyroid panel was obtained twice. Both times the PTH (23.4 and 46.4 pmol/L, normal = 2.91 to 4.57 pmol/L) and ionized calcium (1.68 and 2.10 mmol/L, normal = 1.31 to 1.37 mmol/L) were increased above values for adult females with normal calcium concentration. A tentative diagnosis of primary hyperparathyroidism was made. After a gamma-radiation scan and magnetic resonance imaging of the neck were done, exploratory surgery was performed to identify and remove the affected gland. After gland removal, the baboon's serum calcium, PTH (1.6 pmol/L), and ionized calcium (1.59 mmol/L) values decreased. Results of histologic examination confirmed the diagnosis of benign solitary parathyroid adenoma.

Bilateral thyroidectomy is a commonly indicated treatment for feline hyperthyroidism. The most common postoperative complication is hypocalcemia due to disruption of the parathyroid glands. When parathyroid gland disruption is obvious, many authors suggest autotransplantation (AT) of the glands. This technique never has been supported by a scientific study which monitored postoperative calcium or parathyroid hormone (PTH) concentrations. Cats in this study each underwent bilateral thyroidectomy and parathyroid AT to mimic a clinical situation. Serum calcium concentrations normalized much quicker than concentrations in previously reported cats undergoing bilateral thyroidectomy and parathyroidectomy. Parathyroid AT greatly reduces morbidity in the parathyroidectomized cat.

The surgical treatment of thyroid cancer in the cat involves excision of one or both thyroid glands while sparing at least one parathyroid gland. The most common postoperative complication of bilateral thyroidectomy is transient hypocalcemia. Most feline thyroid tumors are benign, hyperfunctional thyroid adenomas. Surgical excision is usually curative. Canine thyroid cancer is most commonly malignant and nonfunctional. Successful surgical treatment of canine thyroid cancer depends on histologic and early diagnosis prior to metastasis or invasion of the cancer into adjacent structures within the neck.

Selective parathyroidectomy (PTX) is preferred to thyroparathyroidectomy (TPTX) when specific effects of parathyroid hormone depletion are being studied. However, because of the anatomic proximity of thyroid and parathyroid glands, TPTX often is performed, leaving animals depleted of thyroxine (T4) and calcitonin as well as parathyroid hormone (PTH). In the present study, six normal dogs had parathyroid tissue and about seven-eighths of thyroid tissue removed. This quantity of thyroid tissue was inadequate to maintain normal serum T4 concentrations, despite allowance of 168 days for thyroid recovery. Five of six dogs with reduced renal mass had successful selective PTX and normal serum T4 concentrations at 28 days, when one-half or more of thyroid tissue was spared. We conclude that with attention to the surgical technique, selective PTX can be achieved in a high percentage of dogs and sufficient thyroid tissue spared to maintain euthyroidism.

The time-course of the changes in blood ionized calcium, and in plasma 1,25 dihydroxycholecalciferol (1,25(OH)2D3) concentrations and its free index were studied in hens following suppression and resumption of shell formation and throughout the laying cycle in hens laying hard-shelled eggs, in hens fed a low or normal calcium diet and in hens laying shell-less eggs. The respective roles of the calcium needs for shell formation and of the reproductive status in regulation of 1,25(OH)2D3 production were analysed. Plasma 1,25(OH)2D3 decreased 3 hr after suppression of shell formation following premature egg expulsion and remained lower than that of hens laying hard-shelled eggs when premature expulsion of the eggs was continued for several days. Circulating 1,25(OH)2D3 tended to increase progressively when shell formation was resumed. Ablation of the parathyroid glands abolished this increase. In hens laying hard-shelled eggs, the plasma 1,25(OH)2D3 was higher during the period of shell secretion. Feeding hens a low calcium diet (1.2%) caused a marked increase in the plasma 1,25(OH)2D3. Ionized calcium levels tended to show reciprocal changes to plasma 1,25(OH)2D3 decreasing when calcification took place and increasing after its suppression. In hypercalcemic hens laying shell-less eggs and fed a 3.5% Ca diet, the plasma 1,25(OH)2D3 was at a high level 4 hr after ovulation and diminished thereafter. This additive stimulation does not, therefore, involve the parathyroid gland and may involve hormonal changes induced by ovulation. Vitamin D binding protein (DBP) in the plasma was at a high level in mature hens and was not affected by shell formation. Consequently, the free 1,25(OH)2D3 index fluctuated in parallel with total level of this hormone in mature hens. It is concluded that the calcium demand for shell formation modulates, in the short term, plasma 1,25(OH)2D3, via the homeostatic regulation of blood calcium by PTH, but that a large part of its increase is independent of PTH and is associated with the endocrine events concomitant with ovulation.

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.

Thyroidectomy has become a fairly common surgical procedure in small animals because of the increasing incidence of thyroid tumors. Surgical removal of the thyroid gland can be routine or quite challenging, depending on the species (cat vs. dog) and the size and aggressiveness of the tumor. Many problems may be encountered with these patients, associated both with the disease and with the surgical treatment. Both thyroid and parathyroid tumors result in many alterations in the animal's homeostasis. These alterations must be recognized by the surgeon to maximize the chance of a successful outcome. This chapter deals with thyroidectomy and parathyroidectomy in dogs and cats. Indications for surgery, pathophysiology of thyroid and parathyroid neoplasia, preoperative care, surgical procedures, and postoperative care and complications will be discussed.