Thyroid hormone concentrations differ between donkeys and horses

Reasons for performing study: Reference intervals for thyroid hormones (TH) concentrations have not been previously established for donkeys, leading to potential misdiagnosis of thyroid disease. Objectives: To determine the normal values of TH in healthy adult donkeys and compare them to TH values from healthy adult horses. Methods: Thirty‐eight healthy Andalusian donkeys and 19 healthy Andalusian horses from 2 different farms were used. Donkeys were divided into 3 age groups: <5, 5–10 and >11 years and into 2 gender groups. Serum concentrations of fT3, tT3, rT3, fT4 and tT4 were quantified by radioimmunoassay. All blood samples were collected the same day in the morning. None of the animals had received any treatment for 30 days prior to sampling or had any history of disease. Both farms were in close proximity and under similar management. Differences between groups were determined using a one‐way ANOVA analysis followed by Fisher's LSD test. P<0.05 was considered significant. Results: Serum TH concentrations were higher in donkeys than in horses (P<0.01). Donkeys <5 years had higher serum rT3, fT4 and tT4 concentrations than donkeys >5 years (P<0.05). Furthermore, older donkeys (>11 years) had lower serum fT3 and tT3 concentrations than younger donkeys’ groups (<5 and 5–10 years, P<0.05). TH concentrations were not different between genders (fT3: P = 0.06; tT3: P = 0.08; rT3: P = 0.15; fT4: P = 0.89; and tT4: P = 0.19). Conclusions: Thyroid hormone concentrations are different between healthy adult donkeys and horses. Potential relevance: Establishing species‐specific TH reference ranges is important when evaluating clinicopathologic data in equids in order to avoid the misdiagnosis of thyroid gland dysfunction. Further studies to elucidate the physiological mechanisms leading to these differences are warranted.     

An investigation of the relationships between body condition and plasma lipid and lipoprotein concentrations in 24 donkeys

Obese donkeys are susceptible to a hyperlipaemic crisis characterised by high plasma triglyceride concentrations. In this study, the relationships between the body condition of 24 donkeys and their basal lipid metabolism were investigated. Plasma cholesterol, triglyceride and lipoprotein cholesterol concentrations were measured in healthy donkeys classified according to their body condition as thin, ideal or obese. There were significant differences between the groups in the concentrations of triglyceride and very low density lipoprotein (VLDL), which increased in concentration with body condition (P less than 0.05). Cholesterol, low density lipoprotein (LDL) and high density lipoprotein (HDL) concentrations were similar in all the groups. Triglyceride and VLDL concentrations were positively correlated with body weight (r = 0.82) and plasma free fatty acid concentration (r = 0.48). There were no significant differences in basal plasma concentrations of insulin or cortisol. These results suggest that obesity in donkeys is associated with changes in lipid and lipoprotein metabolism that might predispose the animals to hyperlipaemia.     

Hypertriglyceridemia with increased plasma insulin concentrations in cats

Metabolite, insulin and adiponectin concentrations and LDH, AST and ALT activities were measured in plasma of 142 client-owned cats (1–13 years old, 16 breeds) to set up a new criterion of hypertriglyceridemia (hyper-TG) with increased plasma insulin concentrations for early diagnosis of lipid metabolism abnormality including obesity. 25 cats with over 165 mg/dl of plasma triglyceride (TG) concentrations were decided as hyper-TG with increased plasma insulin concentrations, and prevalence of hyper-TG was 16.7% in young (1–6 years old) and 18.3% in old (>7 years old) cats examined. In the hyper-TG cats, their plasma TG concentrations increased to 6.6–7.4-fold of the values of control cats with 35–50 mg/dl of plasma TG and their plasma cholesterol, FFA and insulin concentrations and LDH and ALT activities increased significantly, whereas their plasma adiponectin concentrations decreased significantly compared to those in the control cats. Hyper-TG cats with significantly increased body weights and plasma insulin and decreased plasma adiponectin seemed to be in early stage of obesity accompanying increased plasma insulin concentrations. Increased TG, insulin, LDH and ALT and decreased adiponectin values in plasma seemed to be key factors for diagnosis of lipid metabolism abnormality at early stage in cats.     

Relationship between plasma progesterone and pregnancy-associated glycoprotein concentrations during early pregnancy in dairy cows

The relationship between the concentration of plasma progesterone (P4) during embryo attachment or at recognition of pregnancy, and that of pregnancy-associated glycoprotein (PAG) was assessed in dairy cows. The outcome of artificial insemination (AI) was classified as positive (AI+), negative (AI?), or late embryonic mortality (EM) by measuring circulating PAG concentrations and by ultrasonography. Based on P4 concentrations at either day 21 or day 15, AI+ and EM cows were classified into ‘low’ (P4 concentrations < mean) and ‘high’ (P4 concentrations > mean) P4 groups. In both experiments, the threshold of P4 concentration between the ‘low’ and ‘high’ groups was approximately 6 ng/mL. PAG concentrations were lower in the ‘low’ group only when P4 concentrations were below the threshold. The study findings suggest that a possible P4 threshold exists below which PAG secretion may be impaired.     

Relationship between growth and plasma concentrations of ghrelin and growth hormone in juvenile beagle dogs

Although the release of growth hormone (GH) is known to be regulated mainly by GH-releasing hormone (GHRH) and somatostatin (SRIF) secreted from the hypothalamus, ghrelin also may be involved in GH release during juvenile period. We have examined plasma concentrations of acylated ghrelin, desacyl ghrelin, and GH in juvenile beagle dogs. Plasma acylated and desacyl ghrelin levels changed through aging; however, there was no closely correlation between ghrelin, body weight and circulating GH levels during juvenile period. The increase in body weight was essentially linear until 8 months of age, whereas plasma GH concentrations exhibited bimodal peaks for the meanwhile. The results suggest that ghrelin may not play internal cueing in GH secretion in juvenile beagle dogs.     

Hepatic enzyme activities and plasma insulin concentrations in diabetic herbivorous voles

The activities of the hepatic glycolytic enzymes glucokinase (GKase) and hexokinase (HKase) in herbivorous Microtus arvalis were very low and the hepatic fructose-1,6-diphosphatase (FDPase) activities were aomost the same as those in C57BL/6J mice. Glycosuria was observed in over 50% of voles fed on a low fibre, high concentrate diet. Voles with a high incidence of glycosuria for over 6 weeks became insulin deficient. In these diabetic voles, the hepatic GKase, HKase and FDPase activities decreased considerably as a result of diminished insulin secretion and fatty degeneration of the hepatic cells. It was considered that M. arvalis would be a useful animal model in which to study disorders of glucose utilization in herbivora.     

Yohimbine increases plasma insulin concentrations and reverses xylazine-induced hypoinsulinemia in dogs

Xylazine (1.1 mg/kg of body weight, IV), an alpha 2-adrenoreceptor agonist, suppressed the increase in plasma insulin concentration induced by glucose (0.6 g/kg, IV) in dogs. Yohimbine (0.11 mg/kg, IV), an alpha 2-adrenoreceptor antagonist, given 5 minutes after xylazine, reversed effects of xylazine, whereas yohimbine alone increased plasma insulin and decreased plasma glucose concentrations. Seemingly, alpha 2-adrenoreceptors exert a negative control of insulin release.     

Plasma glucose and cortisol responses to exogenous insulin in fasted donkeys

Susceptibility to equine hyperlipaemia is increased by poor food intake. To assess the contribution of changes in insulin sensitivity, plasma glucose and cortisol responses to an intravenous insulin challenge (0·4 kg⁻¹ bodyweight) were compared with those observed after saline administration in six donkeys fasted either overnight or for three days. Three days of fasting decreased both the rate of insulin-induced hypoglycemia and the maximal hypoglycemic response. A transitory increase in plasma cortisol which peaked within one to four hours of insulin administration was observed in three of the six overnight-fasted donkeys and in all of the three-day fasted donkeys; inter-animal variation appeared to exist in the responsiveness of the hypothalamic-pituitary-adrenocortical ( ) axis to stimulation by insulin-induced hypoglycemia. Fasting is likely to present a risk of equine hyperlipaemia, at least in part, by the reduction in tissue sensitivity to the glucoregulatory action of insulin.     

Effect of trauma on plasma glucagon and insulin concentrations in sheep.

Portal plasma glucagon and insulin concentrations were measured before and after acute trauma (liver biosy). The trauma was sufficient to increase glucagon concentrations and depress insulin concentrations. These changes were associated with a marked hyperglycemia. Infusion of glucagon was insufficient to prevent stress inhibition of insulin secretion. The stimulation of glucagon secretion and inhibition of insulin secretion were of about one hour duration. These findings indicate that glucagon and insulin in conjunction with the nervous system may play an important role in the development of stress related hyperglycemia.     

Spontaneously obese dogs exhibit greater postprandial glucose, triglyceride, and insulin concentrations than lean dogs

Dogs do not appear to progress from obesity-induced insulin resistance to type 2 diabetes mellitus. Both postprandial hyperglycemia and postprandial hypertriglyceridemia have been proposed to cause or maintain beta cell failure and progression to type 2 diabetes mellitus in other species. Postprandial glucose, triglyceride, and insulin concentrations have not been compared in lean and obese dogs. We measured serum glucose, triglyceride, and insulin concentrations in nine naturally occurring obese and nine age- and gender-matched lean dogs. After a 24-h fast, dogs were fed half their calculated daily energy requirement of a standardized diet that provided 37% and 40% of metabolizable energy as carbohydrate and fat, respectively. Fasting and postprandial glucose and triglyceride concentrations were greater in the obese dogs (P < 0.001), although the mean insulin concentration for this group was five times greater than that of the lean group (P < 0.001). Most of the 0.6 mM (11 mg/dL) difference in mean postprandial glucose concentrations between lean and obese dogs was attributable to a subset of persistently hyperglycemic obese dogs with mean postprandial glucose concentrations 1.0 mM (18 mg/dL) greater than that in lean dogs. Persistently hyperglycemic obese dogs had lower triglyceride (P = 0.02 to 0.04) and insulin (P < 0.02) concentrations than other obese dogs. None of the dogs developed clinical signs of diabetes mellitus during follow-up for a median of 2.6 yr. We conclude that pancreatic beta cells in dogs are either not sensitive to toxicity because of mild hyperglycemia or lack another component of the pathophysiology of beta cell failure in type 2 diabetes mellitus.     

Relationship between plasma leptin concentrations and carcass composition in fattening mutton: a comparison with ultrasound results

Positive relationships between circulating leptin concentrations and body fat content have been established in sheep when covering a rather broad range of age and/or body weight. The usefulness of leptin measurements for predicting carcass fat has yet to be evaluated specifically in fattening lambs. We therefore measured plasma leptin concentrations in 56 male lambs half and half Merino Mutton and Blackheaded Mutton. Subcutaneous fat thickness was measured by ultrasound 1 day before the lambs were slaughtered at 35 or 45 kg live weight. Carcass composition was determined by tissue dissection. The coefficients of correlations between leptin and the different amounts in fat depots ranged from 0.40 to 0.56 within the two live weight groups, and from 0.53 to 0.64 when taking the two groups together. Carcass fat percentage was estimated by leptin concentrations with the same accuracy (R2 = 0.34) as with ultrasound fat thickness. The accuracy was higher for leptin in the 35 kg-group whereas the accuracy was higher for ultrasound fat thickness in the 45 kg-group (R2 = 0.26 vs. 0.31). A combination of leptin and ultrasound fat thickness clearly enhanced the precision of estimation in all groups. Further investigations on the influence of factors such as breed, gender, duration of feed withdrawal or photoperiod on the association between leptin and carcass composition are necessary before the suitability of plasma leptin concentration for practical application can be evaluated.     

Relationship between milk production and plasma concentrations of oxidative stress markers during hot season in primiparous cows

Oxidative stress markers, ascorbic acid, and sulfhydryl (SH) residue concentration in primiparous cows' plasma and their relationship to milking performance during hot seasons were investigated. The rectal temperature of cows correlated negatively with SH residue (r = −0.38, n  = 38, P  < 0.05) and ascorbic acid (r = −0.34, P  < 0.05) concentrations in the cows' plasma. The group with a higher concentration of ascorbic acid over the mean value produced significantly more milk ( P  < 0.05) than did the group with a lower ascorbic acid concentration. Although the cows' milk production showed a positive correlation with ascorbic acid concentration in plasma (r = 0.47, P  < 0.05), the relation of SH residue concentration to milk yield was not constant. The plasma SH residue concentration during the hot season correlated positively with milk protein % (r = 0.38, P  < 0.05), lactose % (r = 0.35, P  < 0.05), and solid-non-fat (SNF) % (r = 0.47, P  < 0.05), respectively, but not with fat %. On the other hand, ascorbic acid concentration in plasma showed negative correlations with milk fat % (r = −0.34, P  < 0.05) and protein % (r = −0.49, P  < 0.05), but correlated positively with lactose % (r = 0.52, P  < 0.05). The produced amount (g/day) of milk protein (r = 0.42, P  < 0.05), lactose (r = 0.61, P  < 0.05), and SNF (r = 0.56, P  < 0.05) showed positive correlations with ascorbic acid concentration in plasma.     

Physical characteristics, blood hormone concentrations, and plasma lipid concentrations in obese horses with insulin resistance

OBJECTIVE: To compare obese horses with insulin resistance (IR) with nonobese horses and determine whether blood resting glucose, insulin, leptin, and lipid concentrations differed between groups and were correlated with combined glucose-insulin test (CGIT) results. ANIMALS: 7 obese adult horses with IR (OB-IR group) and 5 nonobese mares. PROCEDURES: Physical measurements were taken, and blood samples were collected after horses had acclimated to the hospital for 3 days. Response to insulin was assessed by use of the CGIT, and maintenance of plasma glucose concentrations greater than the preinjection value for > or = 45 minutes was used to define IR. Area under the curve values for glucose (AUC(g)) and insulin (AUC(i)) concentrations were calculated. RESULTS: Morgan, Paso Fino, Quarter Horse, and Tennessee Walking Horse breeds were represented in the OB-IR group. Mean neck circumference and BCS differed significantly between groups and were positively correlated with AUC values. Resting insulin and leptin concentrations were 6 and 14 times as high, respectively, in the OB-IR group, compared with the nonobese group, and were significantly correlated with AUC(g) and AUC(i). Plasma nonesterified fatty acid, very low-density lipoprotein, and high-density lipoprotein-cholesterol (HDL-C) concentrations were significantly higher (86%, 104%, and 29%, respectively) in OB-IR horses, and HDL-C concentrations were positively correlated with AUC values. CONCLUSIONS AND CLINICAL RELEVANCE: Measurements of neck circumference and resting insulin and leptin concentrations can be used to screen obese horses for IR. Dyslipidemia is associated with IR in obese horses.     

Relationship between plasma concentrations and analgesia after intravenous fentanyl and disposition after other routes of administration in cats

Data allowing rational use of analgesics in cats are limited. Pharmacokinetics and pharmacodynamics of fentanyl were studied in cats. Plasma fentanyl concentrations were measured using radioimmunoassay in a crossover study in six cats after 10 microg/kg (i.v.) or by application of fentanyl in pluronic lecithin organogel (PLO) to the inner ear pinna. On a separate occasion thermal thresholds were measured after i.v. fentanyl (10 microg/kg) or saline. Plasma fentanyl concentrations reached 4.7-8.31 ng/mL 2 min after i.v. administration and were undetectable after 95 min. Fentanyl was not detected in plasma at any time after PLO use. Thermal thresholds did not change following saline administration but were increased above baseline from 5 to 110 min after i.v. fentanyl. In this model a plasma concentration of >1.07 ng/mL was required to provide analgesia. Plasma concentrations were measured in additional cats after intranasal or oral dosing (2 microg/kg) and after 30 microg/kg in PLO gel. After oral and nasal dosing, Cmax values were 0.96 and 1.48 ng/mL at 5 and 2 min, respectively. Plasma fentanyl was not detected after application of the higher dose of fentanyl in PLO.     

Relationship of plasma lipid concentrations to fat deposition in pigs

The time course for changes in plasma free fatty acid and triglyceride concentration after removal of feed was established. Genetically obese and lean lines of pigs, two types of crossbred female pigs and a group of male pigs were used to establish the relationship between circulating free fatty acid or triglyceride concentrations and adiposity. Pigs were weighed, ultrasonically probed for backfat thickness, bled in a fed state and again in the fasted state. Plasma was analyzed for free fatty acid and triglyceride concentration. Fasting increased plasma free fatty acid, but only slightly increased triglyceride concentrations. There were several significant correlations between backfat thickness and plasma lipid concentrations; however, the low magnitude and inconsistency of these correlations precludes use of plasma lipid concentrations as indicators of adiposity in swine. Fasted obese pigs had lower plasma fatty acid concentrations than lean pigs at 2, 4 and 6 mo of age. If these plasma levels represent in vivo mobilization of fat, the results probably contrast with previously reported in vitro results wherein adipose tissue from obese pigs had lipolytic rates expressed on a cellular basis that were equal to or greater than those form lean pigs.     

Effects of topical application of amitraz on plasma glucose and insulin concentrations in dogs

Amitraz, a formamidine insecticide, is used topically in the treatment of demodicosis and other ectoparasitic infestations. When 3.78 L (containing 2.1 g) of amitraz (twice the recommended concentration) was applied to 5 dogs 4 hours before glucose (0.6 g/kg of body weight) was administered IV, plasma glucose concentration increased, but the increase in plasma insulin concentration, which usually follows IV administered glucose, was suppressed. The results suggested that amitraz induced hyperglycemia at least partly by inhibiting insulin release.     

Serum concentrations of calcium, phosphorus, magnesium and calciotropic hormones in donkeys

OBJECTIVE: To provide reference values for serum biochemical variables that are used for evaluation of mineral metabolism in donkeys and compare values with those in horses. ANIMALS: 18 donkeys and 18 horses. PROCEDURES: Total calcium (tCa), total magnesium (tMg), and inorganic phosphorus (P) concentrations were measured in serum samples via spectrophotometry. Ionized calcium (iCa) and magnesium (iMg) concentrations were quantified with selective electrodes. By use of a micropartition system, tCa and tMg were fractionated to separate protein-bound (pCa, pMg) and ultrafiltrable fractions. Complexed calcium (cCa) and magnesium (cMg) concentrations were calculated by substracting ionized fractions from ultrafiltrable fractions. Parathyroid hormone (PTH) and calcitriol (CTR) concentrations were measured via radioimmunoassay. RESULTS: Serum tCa concentration in donkeys (3.37 +/- 0.21 mmol/L) was composed of pCa (1.59 +/- 0.21 mmol/L [47.0 +/- 4.2%]), iCa (1.69 +/- 0.04 mmol/L [50.4 +/- 3.0%]), and cCa (0.09 +/- 0.08 mmol/L [2.6 +/- 2.9%]). Serum tMg concentration (1.00 +/- 0.08 mmol/L) was fractioned in pMg (0.23 +/- 0.08 mmol/L [23.4 +/- 8.1%]), iMg (0.59 +/- 0.04 mmol/L [58.8 +/- 5.1%]), and cMg (0.18 +/- 0.08 mmol/L [17.8 +/- 7.2%]). Serum concentrations of P (1.14 +/- 0.30 mmol/L), PTH (20.4 +/- 21.2 pg/mL), and CTR (13.4 +/- 5.9 pg/mL) were determined. CONCLUSIONS AND CLINICAL RELEVANCE: Serum variables of mineral metabolism in donkeys were within reference ranges for horses. However, when compared with horses, donkeys had higher iCa, cMg, and CTR and lower pMg and PTH concentrations.     

Correction for sample free glycerol is needed for accurate measurement of plasma triglyceride concentrations in miniature Swine

Methods for the measurement of plasma or serum triglyceride concentrations usually quantify the glycerol released by enzymatic hydrolysis of the triglyceride molecule. Any free glycerol in the sample is measured erroneously as triglyceride in these methods. As miniature swine have been used commonly for comparative studies of plasma lipoprotein lipids, this study was conducted to assess the need for free glycerol correction of plasma triglyceride measurements by comparing glycerol-blank corrected and non-corrected total plasma triglyceride concentrations from fasted minipigs. Fasting plasma free glycerol concentrations range from 9 to 14 mg/dl. The mean +/- SD (n = 16) glycerol-blank corrected total plasma triglyceride value (77 +/- 8 mg/dl) was significantly (p < 0.001) less than the uncorrected measurement value (189 +/- 12 mg/dl). Poor correlation (r = 0.24) between corrected and uncorrected total plasma triglyceride measurements suggests that mathematic correction by a constant correction factor would yield inaccurate results for miniature swine. Free glycerol blanking is essential for determination of the true total plasma triglyceride concentration.