ULTRASONOGRAPHIC EXAMINATION OF THE THYROID GLAND OF HYPERTHYROID CATS: COMPARISON TO 99mTcO−4 SCINTIGRAPHY

High-resolution ultrasonography was evaluated as an alternative to ^99mTcO^-₄ scintigraphy for examining size and appearance of thyroid glands in hyperthyroid cats. Thyroid ultrasound examinations were performed on 6 normal cats and 14 cats with hyperthyroidism. Thyroid lobe volume was estimated from ultrasound images using the equation for a prolate ellipsoid, π/6 (length * height * width). Total thyroid volume was estimated by adding the volume estimations of the left and right lobes. Thyroid lobes of hyperthyroid cats were considered abnormal if estimated volume exceeded the 99% confidence interval for normal thyroid volume determined from the control group. Scintigraphic examinations performed on hyperthyroid cats were evaluated for unilateral versus bilateral disease and for the presence of ectopic activity. Mean thyroid lobe volume and total thyroid volume for normal cats was 85 and 169 mm³, respectively. Mean thyroid lobe volume and total thyroid volume for hyperthyroid cats was 578 and 889 mm³. There was a significant difference in mean estimated total thyroid volume of normal and hyperthyroid cats. Thyroid lobes with greater than normal TcO^-₄ uptake on scintigraphy were larger and had variable homogeneity, echogenicity, and margination on ultrasound examination. There also was an 85.7% agreement of scintigraphy and ultrasonography in differentiating normal from abnormal thyroid lobes. A fair correlation between estimated total thyroid volume of hyperthyroid cats and most recent pretherapy serum thyroxine values were also found. This preliminary study indicates that thyroid ultrasound examination may provide information that is useful for diagnosis and treatment of feline hyperthyroidism. Although ultrasound provides accurate evaluation of the thyroid glands, it cannot replace ^99mTcO^-₄ scintigraphy for screening of metastatic lesions and ectopic glands.     

RADIONUCLIDE THYROID IMAGING IN 135 CATS WITH HYPERTHYROIDISM*

Thyroid scanning was performed in 135 hyperthyroid cats and 13 normal cats with technetium-99m as pertechnetate (^99mTcO₄) or with radioactive iodine (¹³¹I). Of the hyperthyroid cats, enlargement and increased radionuclide accumulation were found in one thyroid lobe in 38 (27%) and in both lobes in 97 (73%). In two hyperthyroid cats with thyroid carcinoma, extension of tumor into the thoracic cavity was detected. In normal and hyperthyroid cats the radionuclide images produced with ^99mTcO₄ and ¹³¹I were similar; however, the quality of the ^99mTcO₄ scans was usually better than that of the ¹³¹I scans.     

QUANTITATIVE PERTECHNETATE THYROID SCINTIGRAPHY AND THE ULTRASONOGRAPHIC APPEARANCE OF THE THYROID GLAND IN CLINICALLY NORMAL HORSES

We characterized the scintigraphic and sonographic appearance of the thyroid gland in clinically normal horses to establish the value of these modalities for assessment of the thyroid gland in this species. Horses were divided into two age groups. One group consisted of eight horses between 3 and 10 years of age and the other of seven horses between 11 and 20 years of age. Total T₄ concentrations were within the laboratory reference interval in all horses. Thyroid to salivary (T/S) ratio, percent dose uptake of pertechnetate (Na^99mTcO₄) and thyroid lobe volume were calculated. The echogenicity of thyroid lobes and presence of nodules was documented. The two groups were compared using appropriate parametric and nonparametric statistics. Mean total T₄ concentration was lower in older horses. Sixty minute mean±standard deviation (SD) T/S ratios for old vs. young horses were 5.8±3.0 and 5.3±2.2, respectively. Sixty‐minute median and interquartile ranges for percent dose uptake of pertechnetate for old vs. young horses were 3.64% (1.5–3.98%) and 2.55% (2.33–2.90%), respectively. Mean±SD thyroid lobe volume for old vs. young horses were 18.93±5.16 cm ³ and 13.55±3.56 cm³, respectively. Differences between groups were not significant. Most thyroid lobes were hyper or isoechoic to the sternocephalicus muscle. Prevalence of thyroid nodules did not differ between groups. Further study is needed to determine if thyroidal percent dose uptake is significantly different in horses with thyroid dysfunction and if it is clinically useful.     

THYROID SCINTIGRAPHY FINDINGS IN 2096 CATS WITH HYPERTHYROIDISM

Thyroid scintigraphy is currently the reference standard for diagnosing and staging cats with hyperthyroidism, but few studies describing the scintigraphic characteristics in a large number of cats have been reported. The objective of this study was to better characterize thyroid scintigraphy findings by evaluating 2096 consecutive cats with hyperthyroidism that were referred over a 3.5‐year period. Of these cats, 2068 (98.7%) had a high thyroid‐to‐salivary ratio (>1.5), whereas 2014 (96.1%) were found to have a high thyroid‐to‐background ratio (>6.1). When the patterns of the cats’ thyroid disease were recorded, 665 (31.7%) had unilateral disease, 1060 (50.6%) had bilateral‐asymmetric disease (two thyroid lobes unequal in size), 257 (12.3%) had bilateral‐symmetric disease (both lobes similar in size), and 81 (3.9%) had multifocal disease (≥3 areas of increased radionuclide uptake). The number of areas of ^99mTcO^?₄ uptake in the 2096 cats ranged from 1 to 6 (median, 2), located in the cervical area in 2057 (98.1%), thoracic inlet in 282 (13.5%), and in the thoracic cavity in 115 (5.5%). Ectopic thyroid tissue (e.g. lingual or mediastinal) was diagnosed in 81 (3.9%) cats, whereas thyroid carcinoma was suspected in 35 (1.7%) of the cats. The results of this study support conclusions that most hyperthyroid cats have unilateral or bilateral thyroid nodules, but that multifocal disease will develop in a few cats that have ectopic thyroid disease or thyroid carcinoma. Both ectopic thyroid disease and thyroid carcinoma are relatively uncommon in hyperthyroid cats, with a respective prevalence of ～4% and ～2% in this study.     

Effect of medetomidine-butorphanol and dexmedetomidine-butorphanol combinations on intraocular pressure in healthy dogs

ObjectiveTo assess the effects of intravenous (IV) medetomidine-butorphanol and IV dexmedetomidine-butorphanol on intraocular pressure (IOP).Study designProspective, randomized, blinded clinical study.AnimalsForty healthy dogs. Mean ± SD body mass 37.6 ± 6.6 kg and age 1.9 ± 1.3 years.MethodsDogs were allocated randomly to receive an IV combination of dexmedetomidine, 0.3 mg m^?2, combined with butorphanol, 6 mg m^?2, (group DEX) or medetomidine 0.3 mg m^?2, combined with butorphanol 6 mg m^?2, (group MED). IOP and pulse (PR) and respiratory (f_R) rates were measured prior to (baseline) and at 10 (T10), 20 (T20), 30 (T30) and 40 (T40) minutes after drug administration. Oxygen saturation of hemoglobin (SpO₂) was monitored following sedation. Data were analyzed by anova followed by Dunnett's tests for multiple comparisons. Changes were considered significant when p < 0.05.ResultsFollowing drug administration, PR and f_R were decreased significantly at all time points but did not differ significantly between groups. Baseline IOP in mmHg was 14 ± 2 for DEX and 13 ± 2 for MED. With both treatments, at T10, IOP increased significantly (p < 0.001), reaching 20 ± 3 and 17 ± 2 for DEX and MED respectively. This value for DEX was significantly higher than for MED. There were no significant differences in IOP values between groups at any other time points. At T30 and T40, IOP in both groups was below baseline (DEX, 12 ± 2 and 11 ± 2: MED 12 ± 2 and 11 ± 2) and this was statistically significant, for DEX.Conclusions and clinical relevanceAt the documented doses, both sedative combinations induced a transient increase and subsequent decrease of IOP relative to baseline, which must be taken into consideration when planning sedation of animals in which marked changes in IOP would be undesirable.     

EVALUATION OF QUANTITATIVE THYROID SCINTIGRAPHY FOR DIAGNOSIS AND STAGING OF DISEASE SEVERITY IN CATS WITH HYPERTHYROIDISM: COMPARISON OF THE PERCENT THYROIDAL UPTAKE OF PERTECHNETATE TO THYROID‐TO‐SALIVARY RATIO AND THYROID‐TO‐BACKGROUND RATIOS

Thyroid scintigraphy is commonly used for evaluation of cats with hyperthyroidism, with the thyroid‐to‐salivary ratio (T/S) being the most common method to quantify the degree of thyroid activity and disease. Calculation of thyroid‐to‐background ratios (T/B) or percent thyroidal uptake of ^99mTcO^?₄ (TcTU) has only been reported in a few studies. The purpose of this prospective, cross‐sectional study was to evaluate a number of quantitative scintigraphic indices as diagnostic tests for hyperthyroidism, including the T/S, three different T/B, TcTU, and estimated thyroid volume. Of 524 cats referred to our clinic for evaluation of suspected hyperthyroidism, the diagnosis was confirmed (n = 504) or excluded (n = 20) based on results of a serum thyroid panel consisting of thyroxine (T₄), triiodothyronine (T₃), free T₄ (fT₄), and thyroid‐stimulating hormone (TSH) concentrations. In the hyperthyroid cats, median values for TcTU, T/S, and three T/B ratios were all significantly higher (P < 0.001) than values in euthyroid suspect cats or clinically normal cats. All scintigraphic parameters were relatively sensitive and specific as diagnostic tests for hyperthyroidism, but the T/S ratio had the highest test accuracy. The T/S ratio correlated strongly with the TcTU (r = 0.85). However, the TcTU had a higher and more significant correlation (P < 0.01) with serum T₄ (r = 0.76 vs. 0.64), T₃ (r = 0.77 vs. 0.64), and estimated thyroid volume (r = 0.62 vs. 0.38). Overall, calculation of TcTU is an accurate diagnostic test, but also appears to be the best parameter to predict the functional volume and metabolic activity of the feline adenomatous thyroid gland.     

The use of nuclear imaging for a mixed C cell microfollicular carcinoma of the thyroid gland in a mature horse

A 15‐year‐old Boerperd stallion presented for thyroid enlargement associated with inappetance. Ultrasonographic examination of the thyroid gland revealed an enlarged left lobe, which, on cytological examination, contained numerous anaplastic cells. A mixed C cell microfollicular thyroid carcinoma was diagnosed following histopathological examination of the excisional biopsy specimen. In order to determine metastasis, pulmonary radiographs revealed a poorly‐marginated soft tissue opacity caudo‐dorsal to the cardiac silhouette. Thyroid and pulmonary scintigraphy was performed comparing ^99mTc‐sestamibi with ^99mTc‐pertechnetate and no metastasis was detectable. Following hemithyroidectomy, the stallion made a full recovery without the need for neoadjuvant chemotherapy. Six months later, repeated thyroid and pulmonary scintigraphy using ^99mTc‐sestamibi was normal.     

Comparison of the pharmacokinetics and thermal antinociceptive pharmacodynamics of 20 µg kg−1 buprenorphine administered sublingually or intravenously in cats

Little is known about the analgesic action of buprenorphine (BUP) in cats. Relative to man, the cat has a more alkaline oral pH, which may make this an effective route for administering BUP in this species. This study aimed to assess and compare the pharmacokinetics and pharmacodynamics of sublingual (S‐L) and IV administration of BUP. Thermal threshold (TT) was measured and blood samples were collected following IV or S‐L administration (20 µg kg^?1) of the injectable formulation. Six cats (five spayed females, one castrated male, 4.1–6.6 kg) were used. Each cat received both treatments in a randomized cross‐over study design with 1 month between experiments. Twenty‐four hours prior to each study, the lateral thorax of each of the cats was shaved, cephalic and jugular catheters placed, and oral pH measured. On the day of the study, TT was measured using a ‘thorax‐mounted’ thermal threshold‐testing device specifically developed for cats. The cats were free to move around. Skin temperature was recorded before each test, then the heater activated. When the cat responded by flinching, turning, or jumping, the stimulus was terminated and the threshold temperature was recorded. The thermal threshold cut‐off point was 55.5 °C. Three baseline thresholds were recorded before treatment with S‐L or IV (via cephalic catheter) BUP (20 µg kg^?1). Blood was withdrawn (jugular) at 1, 2, 4, 6, 10, 15, 30, 45, 60 minutes and at 2, 4, 6, 8, 12, and 24 hours post‐administration. TT was measured every 30 minutes?6 hours, 1–12 hours, and at 24 hours post‐administration. Plasma was immediately separated, stored at ?20.5 °C, and assayed within 4 months using a commercially available ¹²⁵I radioimmunoassay. Threshold data were analyzed using anova with a repeat factor of time. No adverse effects were noted. Pupils were dilated for up to 9 hours post‐BUP. Behavioral changes were calm euphoria. Measured oral pH was 9 in each cat. Pre‐treatment mean threshold (±SD) was 41.2 ± 0.9 °C in the S‐L group and 40.8 ± 0.85 °C in the IV group. There were no significant differences between the groups with respect to thresholds over time (p = 0.72). Thresholds were significantly increased from 30 to 360 minutes in both the groups (>44.615 °C). Peak plasma BUP (C_max) was lower (11 ± 6.7 ng mL^?1vs. 92.9 ± 107.9 ng mL^?1) and occurred later (T_max) (30 minutes vs. 1 minute) after S‐L compared to IV administration, respectively. BUP (20 µg kg^?1)‐administered S‐L or IV provided antinociception between 30 and 360 minutes after administration. Plasma levels did not correspond to TT.     

DIURETIC RENAL SCINTIGRAPHY IN NORMAL CATS

The purpose of this study was to develop a protocol for diuretic renal scintigraphy (renography) in cats and describe normal findings. ^99mTc‐DTPA renal scintigraphy was performed twice in 10 healthy cats. Furosemide or saline were injected 4.5 min after radiopharmaceutical administration for the diuretic or control scan, respectively. A dynamic acquisition was performed for 8 min. The following parameters were evaluated: (1) global and individual glomerular filtration rate (GFR); (2) shape of the time–activity curve (TAC); (3) time of peak (TOP); (4) individual kidney excretion half‐time (T_1/2) of the radiopharmaceutical; (5) percentage of maximum activity measured at the end of the study. Global GFR in the control studies (2.79±0.83 ml/min/kg, mean±SD) did not differ significantly from the diuretic scans (2.34±0.51 ml/min/kg). The shape of most (16/20) TAC of diuretic renograms was similar to those of control renograms. The TOP of the diuretic renogram curves was 3.06±0.58 min, and did not differ from that of the control scans (3.01±0.61 min). T_1/2 of the diuretic renograms was significantly shorter (5.15±0.83 min) than that of the control renograms (6.31±1.50 min). A significantly lower percentage of maximum activity was present at the end of the study in diuretic renograms (median: 47.25%; range: 33.60–59.60%) compared with control renograms (63.40%; 30.00–69.40%). Diuretic renal scintigraphy is a noninvasive and fast procedure to perform in cats. The applicability of this technique needs to be investigated in patients with significantly impaired renal function and obstructive uropathies.     

COMPARISON BETWEEN COMPUTED TOMOGRAPHY AND 99m TC‐ PERTECHNETATE SCINTIGRAPHY CHARACTERISTICS OF THE THYROID GLAND IN CATS WITH HYPERTHYROIDISM

Scintigraphy is currently the reference standard for diagnosing feline hyperthyroidism; however, computed tomography (CT) is more widely available in veterinary practice. The purposes of this prospective study were to describe the CT appearance of thyroid glands in cats with hyperthyroidism and compare CT findings with findings from ^99mTc–pertechnetate scintigraphy. Twenty‐five adult hyperthyroid cats were included. Plain CT images were acquired for each cat and the following characteristics recorded for each thyroid lobe: visibility, delineation, position, attenuation, shape, and subjective size. Scintigraphic images were also acquired and the following characteristics recorded: radiopharmaceutical uptake, delineation, ectopic foci, shape, and subjective size. In CT images, thyroid lobes were most commonly found between the second and fourth cervical vertebrae, dorsolateral to the trachea. Affected thyroid lobes (based on scintigraphy reference standard) were most commonly oval and moderately enlarged in CT images. A heterogeneous attenuation pattern (isoattenuating to adjacent soft tissues with hypo‐ and hyperattenuating foci) was most commonly found in affected thyroid lobes. A positive correlation (P < 0.01) was identified between CT and scintigraphy for left‐to‐right thyroid lobe size relationship and subjective size of the larger thyroid lobe. The CT estimated mass was significantly higher (median = 148.8; range = [0;357.6]) for the more active thyroid lobe compared to the less active thyroid lobe (median = 84.6; range = [0;312.3]); (W = 154; P < 0.01). Findings indicated that CT may not reliably differentiate unilateral vs. bilateral hyperthyroidism in cats; however, CT may be a reliable alternative test for correctly identifying the more active thyroid lobe.     

Radioactive iodine therapy for feline hyperthyroidism: Efficacy and administration routes

The efficacy of radioactive iodine (¹³¹I) administration was studied in a series of 50 hyperthy-roid cats. The dose administered to each cat was based on the clinical severity of the thyrotoxicosis, the serum total thyroxine (TJ concentration and the size of the goitre estimated by palpation. The activity ranged from 80 to 200 MBq (mean ± SD, 143 ± 24 MBq}. The ¹³¹I was injected intravenously in 27 cases and subcutaneously in 23 cases. Each cat was hospitalised for 30 days after the injection. Regardless of the route of injection, none of the cats exhibited any side effects after therapy and all tolerated the hospitalisation period well. There was a significant (P<0.001) decrease in the serum total T₄ concentration (reference range, 10.4 to 42.0 nmol/litre) from a mean ± SD of 181.3 ± 111.4 nmol/litre (range, 43.8 to 575.6 nmol/litre) to a mean ± SD of 19.0 ± 29.6 nmol/litre (range, 2.0 to 175.7 nmol/litre) 30 days following the injection of the radioisotope. Five cats remained hyperthyroid, although in each case the serum total T₄ concentrations had decreased from pre-treatment values. Two of the cats subsequently became euthyroid within three and five months of therapy, respectively, two were lost to adequate follow-up and the remaining cat was successfully retreated four months later. Before treatment, four of these cases had high scores based on the three criteria used for dose estimation. Serum total T₄ concentrations below the reference range developed after treatment in many cases, but were often transient. Clinical evidence of hypothyroidism was not apparent in any cat. Recurrence of hyperthyroidism has not occurred in follow-up periods of up to 32 months. There was no difference in the outcome between the cats injected intravenously or subcutaneously and the latter was considered to be safer and simpler. The administration of an approximated dose of ¹³¹I proved to be an effective treatment for hyperthyroidism in 47 (94.0 per cent) of the cats and obviated the need for sophisticated nuclear computer facilities. There may be a lag period in some cases before euthy-roidism is achieved and this should be considered before the administration of a second dose. ¹³¹I can be administered subcutaneously without untoward effects.     

Use of electrical nerve stimulation to monitor lumbosacral epidural needle placement in cats

ObjectiveTo determine the minimal electrical threshold (MET) necessary to elicit muscle contraction of the pelvic limb or tail when an insulated needle is positioned outside (MET_out) and inside (MET_in) the lumbosacral epidural space in cats.Study designProspective, blinded study.AnimalsTwelve mixed-breed healthy adult cats, scheduled for a therapeutic procedure where lumbosacral epidural administration was indicated.MethodsUnder general anesthesia, an insulated needle was advanced through tissues of the lumbosacral interspace until its tip was thought to be just dorsal to the interarcuate ligament. An increasing electrical current (0.1 ms, 2 Hz) was applied through the stimulating needle in order to determine the MET necessary to obtain a muscle contraction of the pelvic limb or tail (MET_out), and then 0.05 mL kg^?1 of iohexol was injected. The needle was further advanced until its tip was thought to be in the epidural space. The MET was determined again (MET_in) and 0.2 mL kg^?1 of iohexol was injected. The cats were maintained in sternal position. Contrast medium spread was determined through lateral radiographic projections.ResultsThe radiographic study confirmed the correct needle placement dorsal to the interarcuate ligament in all cats. When the needle was placed ventrally to the interarcuate ligament, iohexol was injected epidurally in ten and intrathecally in two cats. The MET_out and MET_in was 1.76 ± 0.34 mA and 0.34 ± 0.07 mA, respectively (p < 0.0001).Conclusion and clinical relevanceNerve stimulation can be employed as a tool to determine penetration of the interarcuate ligament but not the piercing of the dura mater at the lumbosacral space in cats.     

Cardiovascular effects following epidural injection of romifidine in isoflurane‐anaesthetized dogs

ObjectiveTo investigate the cardiovascular effects of epidural romifidine in isoflurane-anaesthetized dogs.Study designProspective, randomized, blinded experiment.AnimalsA total of six healthy adult female Beagles aged 1.25 ± 0.08 years and weighing 12.46 ± 1.48 (10.25–14.50) kg.MethodsAnaesthesia was induced with propofol (6–9 mg kg^?1) and maintained with 1.8–1.9% end-tidal isoflurane in oxygen. End-tidal CO₂ was kept between 35 and 45 mmHg (4.7–6.0 kPa) using intermittent positive pressure ventilation. Heart rate (HR), arterial blood pressure and cardiac output (CO) were monitored. Cardiac output was determined using a LiDCO monitor and the derived parameters were calculated. After baseline measurements, either 10 μg kg^?1 romifidine or saline (total volume 1 mL 4.5 kg^?1) was injected into the lumbosacral epidural space. Data were recorded for 1 hour after epidural injection. A minimum of 1 week elapsed between treatments.ResultsAfter epidural injection, the overall means (± standard deviation, SD) of HR (95 ± 20 bpm), mean arterial blood pressure (MAP) (81 ± 19 mmHg), CO (1.63 ± 0.66 L minute^?1), cardiac index (CI) (2.97 ± 1.1 L minute^?1 m^?2) and stroke volume index (SI) (1.38 ± 0.21 mL beat^?1 kg^?1) were significantly lower in the romifidine treatment compared with the overall means in the saline treatment [HR (129 ± 24 bpm), MAP (89 ± 17 mmHg), CO (3.35 ± 0.86 L minute^?1), CI (6.17 ± 1.4 L minute^?1 m^?2) and SI (2.21 ± 0.21 mL beat^?1 kg^?1)]. The overall mean of systemic vascular resistance index (SVRI) (7202 ± 2656 dynes seconds cm^?5 m^?2) after epidural romifidine injection was significantly higher than the overall mean of SVRI (3315 ± 1167 dynes seconds cm^?5 m^?2) after epidural saline injection.ConclusionEpidural romifidine in isoflurane-anaesthetized dogs caused significant cardiovascular effects similar to those reportedly produced by systemic romifidine administration.Clinical relevanceSimilar cardiovascular monitoring is required after epidural and systemically administered romifidine. Further studies are required to evaluate the analgesic effects of epidural romifidine.     

Pharmacokinetics of the novel COX‐2 selective inhibitor vitacoxib in cats: The effects of feeding and dose

The purpose of this study was to determine the pharmacokinetics and dose‐scaling model of vitacoxib in either fed or fasted cats following either oral or intravenous administration. The concentration of the drug was quantified by UPLC‐MS/MS on plasma samples. Relevant parameters were described using noncompartmental analysis (WinNonlin 6.4 software). Vitacoxib is relatively slowly absorbed and eliminated after oral administration (2 mg/kg body weight), with a T_max of approximately 4.7 hr. The feeding state of the cat was a statistically significant covariate for both area under the concentration versus time curve (AUC) and mean absorption time (MAT_fed). The absolute bioavailability (F) of vitacoxib (2 mg/kg body weight) after oral administration (fed) was 72.5%, which is higher than that in fasted cats (F = 50.6%). Following intravenous administration (2 mg/kg body weight), Vd (ml/kg) was 1,264.34 ± 343.63 ml/kg and Cl (ml kg^?1 hr^?1) was 95.22 ± 23.53 ml kg^?1 hr^?1. Plasma concentrations scaled linearly with dose, with C_max (ng/ml) of 352.30 ± 63.42, 750.26 ± 435.54, and 936.97 ± 231.27 ng/ml after doses of 1, 2, and 4 mg/kg body weight, respectively. No significant undesirable behavioral effects were noted throughout the duration of the study.     

Abiotic and herbaceous vegetational characteristics of an arid rangeland in Kenya

A two-year study was conducted with an overall objective of characterising the structure and function of an arid rangeland in Kenya. A plot measuring 100 × 100m was used for this study. Data on rainfall and temperature were recorded at the plot site whereas data on evaporation rates and relative humidity were obtained from the meteorological office near the study site.

Herbaceous aboveground material was sampled at monthly intervals using a rectangular 0.25m² quadrat frame. Clipped material was separated by species and classified dead or live by physical examination. A 5cm diameter metal soil corer was used to sample belowground plant material, at monthly intervals. The sampled material was washed with running water over 2mm sieves and classified dead or live using the vital staining technique. All weights and calculations were based on organic weight.

Total aboveground standing crop ranged from 84.6g m^?2 to 295.4g m^?2, with a mean of 162.3 ± 60.6g m^?2. Mean monthly aboveground standing crop for 1992 and 1993 was 142.8 ± 53.8 and 178.5 ± 63.3g m^?2 respectively. The two values were significantly different (p<0.10). Aboveground biomass yield ranged from 17.7g m^?2 to 242.7g m^?2, with a mean of 104.3 ± 58g m^?2 and a coefficient of variation of 58%. Mean aboveground standing crop was 59 ± 24g m^?2 Monthly values ranged from 28.8g m^?2 to 120g m^?2, with a 38% coefficient of variation.

The range for total belowground standing crop was from 83.3g m^?2 to 232.7g m^?2, and a mean of 155.2 ± 46g m^?2. The values had a coefficient of variation of 30%. Mean total monthly belowground plant material yield for 1992 and 1993 was 137.6 ± 41g m^?2 and 169.9 ± 46g m^?2 The coefficients of variation were 59% and 28% respectively. The mean monthly belowground biomass yield was 51.6 ± 33g m^?2 with a coefficient of variation of 64%. Mean monthly yield for belowground dead material was 103.7 ± 32g m^?2, with a coefficient of variation of 31%. There was no significant difference (p>0.01) in the mean belowground dead material yield between 1992 and 1993.

In 1992, annual NPP was 439.2g m^?2, giving a net primary productivity of 1.22g m^?2day^?l. Monthly NPP ranged from 17.2g m^?2 to 90.1g m^?2 In 1993, annual NPP was 944.5g m^?2, equivalent to a net primary productivity of 2.62g m^?2 day^?1. Monthly NPP was between 27.4g m^?2 and 548.6g m^?2. Over the 1992–1993 period, NPP was 1 383.7g m^?2, equivalent to a productivity of 1.92g m^?2day^?1. Trends in monthly NPP closely followed the trend in rainfall. On the whole, herbaceous vegetation production and productivity were episodic in nature and closely linked to rainfall. The high primary productivity puts arid and semi-arid rangelands under sharp focus as CO₂ sinks, whose role in the amelioration of greenhouse effect could be more important than is currently appreciated.     

Estimation of intestinal permeability in healthy dogs using the contrast medium iohexol

Background: Iohexol is a nonradioactive marker that has been used successfully to test intestinal permeability in humans with inflammatory bowel disease. There is evidence in dogs that iohexol shares a similar permeability pathway as ⁵¹chromium‐EDTA, the gold standard marker. Objective: The objective of this study was to determine an optimal oral iohexol dosage for an intestinal permeability serum test (IPST) and to use the test to estimate intestinal permeability in healthy dogs. Methods: Eight clinically healthy dogs free of gastrointestinal, liver, and pancreatic disease were used in the study. Dosages of 0.25, 0.5, 1.0, 2.0, and 4.0 mL/kg of Omnipaque‐350 (iohexol) were administered to 2 dogs at weekly intervals. Iohexol concentration was determined in serum samples obtained hourly for 6 hours after administration by high‐performance liquid chromatography. Using the optimal dosage, iohexol was administered to 8 dogs twice, 6–36 days (mean 10 days) apart, and coefficients of variation (CVs) for iohexol concentration were calculated. Results: A dosage of 2.0 mL/kg was chosen as optimal for the IPST, based on ease of iohexol detection in serum, intestinal contrast, and clinical effects of iohexol. Following administration of this dose to healthy dogs, mean (±SD) serum iohexol concentrations were 8.74±4.38, 11.89±5.67, 12.40±5.47, 9.23±5.54, 7.61±5.13, and 5.27±2.67 μg/mL at 1, 2, 3, 4, 5, and 6 hours after iohexol administration, respectively. CVs between the 2 test days were 28–45%. Conclusions: Using the iohexol dosage established in this study, the iohexol IPST was easy to perform as a marker for intestinal permeability in dogs. Further studies to establish reference intervals and evaluate the diagnostic value of the iohexol IPST in dogs with gastrointestinal disease are warranted.     

Effects of ketamine‐diazepam and ketamine‐acepromazine combinations on intraocular pressure in rabbits

ObjectiveTo determine the effects of ketamine-diazepam and ketamine-acepromazine combinations on intraocular pressure (IOP) in rabbits.Study designRandomized clinical trial.AnimalsSixteen adult New Zealand white rabbits approximately one year old, weighing 2.3 ± 0.2 kg were used in this study.MethodsThe animals were randomly divided into two groups of eight each (KA and KD). The pre-treatment IOPs were recorded in both groups (T0). All rabbits in group KA received intramuscular ketamine-acepromazine (ketamine 30 mg kg^?1+ acepromazine 0.5 mg kg^?1). Ketamine-diazepam (ketamine 30 mg kg^?1 + diazepam 1 mg kg^?1) was administered intramuscularly in members of group KD. The IOP values were measured at 5 (T₅), 15 (T₁₅), and 20 (T₂₀) minutes after drug administration in both treatment groups.ResultsSignificant increases in IOP values were observed in both treatment groups at T_5, T₁₅, and T₂₀ in comparison to the baseline values. In group KA the mean ± SD IOP at T_5, T₁₅, and T₂₀ were 37 ± 13 (p < 0.001), 35 ± 4 (p < 0.001) and 34 ± 4 mmHg (p < 0.001). The post-treatment mean ± sd values in group KD were 23 ± 8 (p = 0.002), 23 ± 5 (p < 0.001) and 23 ± 6 mmHg (p = 0.001) at 5, 15, and 20 minutes respectively.Conclusion and clinical relevanceBoth ketamine-diazepam and ketamine-acepromazine combinations increased IOP after intramuscular administration in rabbits.     

EFFECTS OF METHIMAZOLE ON THYROID GLAND UPTAKE OF 99MTC-PERTECHNETATE IN 19 HYPERTHYROID CATS

Nineteen cats with abnormally high serum T4 concentrations underwent thyroid scintigraphy using technetium-99m pertechnetate (99mTcO4) before and after 36 +/- 6 days of methimazole administration (approximately 2.5mg PO q 12 h). Thyroid-to-salivary gland ratios (T:S ratios) and percentage thyroidal uptake of injected radioactivity at 20 and 60min after injection of 99mTcO4 were compared before and after methimazole treatment. Serum thyroid stimulating hormone (TSH) concentration was measured before and after methimazole treatment. Quantitatively, there was a positive association between the thyroid uptake of 99mTcO4 and the serum T4 before treatment (r = 0.74-0.83). TSH suppression was present when cats were first evaluated for hyperthyroidism. Methimazole treatment did not relieve TSH suppression in 17 cats. Two cats with unilateral thyroid uptake developed bilateral, asymmetric thyroid uptake of 99mTcO4 after treatment and had the greatest increase in TSH concentration after treatment. Quantitatively, thyroid scintigraphy did not significantly change after methimazole treatment (P>0.1). Evaluation of serum TSH concentration may be helpful in identifying methimazole-induced changes in the scintigraphic features of hyperthyroidism in mildly hyperthyroid cats.     

Effect of four sedative and anesthetic protocols on quantitative thyroid scintigraphy in euthyroid cats

OBJECTIVES: To determine the effect of sedation and anesthesia on thyroid and salivary gland uptake of technetium Tc 99m pertechnetate ((99m)TcO(4)) in euthyroid cats. ANIMALS: 6 euthyroid cats. PROCEDURES: Thyroid scintigraphy was performed by use of a high-resolution low-energy parallel-hole collimator after IV injection of 117 to 133 MBq (3.16 to 3.59 mCi) of (99m)TcO(4)(-). The procedure was performed 4 times on each cat during different sedative and anesthetic protocols in a rotating schedule as follows: propofol, ketamine-midazolam-atropine, ketaminemidazolam, and medetomidine. Regions of interest were drawn around thyroid and salivary glands and counts corrected for background and decay. Percentage of (99m)TcO(4)(-) uptake in salivary and thyroid glands and thyroid-to-salivary gland (99m)TcO(4)(-) uptake ratio were calculated at 20 and 40 minutes. Relative effects of anesthesia and sedation on salivary and thyroid gland (99m)TcO(4)(-) uptake were compared. RESULTS: Significant differences among sedativeanesthetic protocols were found for thyroid gland (99m)TcO(4)(-) uptake, salivary gland (99m)TcO(4)(-) uptake, and thyroid-to-salivary gland (99m)TcO(4)(-) uptake ratio. Thyroid gland (99m)TcO(4)(-) uptake for the ketamine-midazolam protocol at 20 and 40 minutes after (99m)TcO(4)(-) administration was significantly higher than for the propofol protocol. A significant difference in salivary gland(99m) TcO(4)(-) uptake was found between ketamine-midazolam and ketamine-midazolam-atropine protocols at 40 minutes. The thyroid-to-salivary gland (99m)TcO(4)(-) uptake ratio for the ketamine-midazolam protocol was significantly higher at 40 minutes than for propofol or ketamine-midazolam-atropine protocols. CONCLUSIONS AND CLINICAL RELEVANCE: Sedation and anesthesia have a significant effect on thyroid and salivary gland (99m)TcO(4) uptake in euthyroid cats that may interfere with thyroid scintigraphic image interpretation.     

Isoflurane minimum alveolar concentration sparing effects of fentanyl in the dog

Objective

To characterize the isoflurane-sparing effects of a high and a low dose of fentanyl in dogs, and its effects on mean arterial pressure (MAP) and heart rate (HR).