Association between hyperinsulinaemia and laminitis severity at the time of pituitary pars intermedia dysfunction diagnosis.

BACKGROUND: Hyperinsulinaemia is the suspected component of insulin dysregulation having the strongest association with laminitis and occurs variably in equids with pituitary pars intermedia dysfunction (PPID). OBJECTIVES: We hypothesised that magnitude of hyperinsulinaemia correlates with laminitis severity in PPID-affected equids. Furthermore, we hypothesised that owners can be unaware of chronic endocrinopathic laminitis. STUDY DESIGN: Cross-sectional study. METHODS: Serum insulin concentrations, owner-reported laminitis history and radiographic evidence of laminitis were determined in 38 client-owned horses and ponies with confirmed PPID. Laminitis severity was classified into four categories (normal [nonlaminitic], mild, moderate or severe laminitis) based on degree of distal phalangeal rotation. Animals were also categorised as normoinsulinaemic (<20 µU/ml), mildly hyperinsulinaemic (20-50 µU/ml) and severely hyperinsulinaemic (>50 µU/ml). One-way ANOVA, t tests and Fisher's exact tests were performed. RESULTS: While owners reported laminitis in 37% of animals, 76% were laminitic based on study criteria (P = 0.01). Owners reported laminitis more frequently in hyperinsulinaemic vs. normoinsulinaemic animals; recognition increased with severity of hyperinsulinaemia (P = 0.03). Mean insulin concentrations were higher in equids with moderate to severe radiographic laminitis (geometric mean 74.1, 95% confidence interval (CI) 38.4-143.1 uU/ml) vs. those classified radiographically as normal to mild (31.9, 95% CI 21.1-48.1 uU/ml P = 0.03). MAIN LIMITATIONS: Dynamic insulin testing was not performed; some normoinsulinaemic animals might have had subtle insulin dysregulation. CONCLUSIONS: Although radiographic abnormalities were present in most animals at the time of PPID diagnosis, chronic laminitis remained unrecognised by many owners. Owner awareness of laminitis increased with severity of hyperinsulinaemia and higher insulin concentrations were detected in association with more severe radiographic changes. The Summary is available in Chinese - See Supporting Information.

Effects of age and diet on glucose and insulin dynamics in the horse.

BACKGROUND: Age and diet may affect insulin sensitivity (SI) but these factors have received limited investigation in horses. OBJECTIVES: To measure minimal model parameters during an insulin-modified frequently sampled intravenous glucose tolerance test (FSIGTT) after adaptation to a forage only diet (HAY) or forage supplemented with either starch/sugar-rich (SS) or oil/fibre-rich (FF) concentrate feeds; and to assess glucose and insulin responses to a standardised meal challenge (SMC, 4 g/kg BW of SS) after diet adaptation in adult and aged mares. STUDY DESIGN: Latin square design with eight adult (5-12 years) and nine aged (>19 years) healthy mares. METHODS: Diets were fed for 6 weeks, and the FSIGTT and SMC were performed after 31-32 and 41 days on each diet respectively. Data were analysed by a mixed ANOVA for repeated measures. RESULTS: Acute insulin response to glucose (AIRg) was greater and SI was lower in aged horses, compared with adults, regardless of diet. Both AIRg and SI were greater in aged mares after adaptation to SS, as compared with HAY. Similar trends, although not statistically significant, were observed after adaptation to SS in adult mares. Peak insulin concentration and area under the insulin vs. time curve during the SMC were greater in aged than adult mares with all diets. Furthermore, area under the glucose vs. time curve was lower after adaptation to SS, when compared with other diets, in both groups. MAIN LIMITATIONS: Transient weight loss occurred at the beginning of the study and only one sex was included. Incomplete ingestion of the SMC by four mares was another limitation. CONCLUSIONS: Insulin responses to i.v. and enteral nonstructural carbohydrate challenge increase with age in healthy horses, regardless of diet fed.

Severe hypertriglyceridaemia in horses and ponies with endocrine disorders.

REASONS FOR PERFORMING THE STUDY: Severe hypertriglyceridaemia in horses and ponies with endocrine disorders has been reported anecdotally but has not been documented in the literature. OBJECTIVES: To describe historical and clinicopathological findings as well as progression and outcome in horses and ponies with severe hypertriglyceridaemia (serum triglyceride concentration >5.65 mmol/l) secondary to an endocrine disorder that were otherwise apparently healthy. METHODS: Cases from 6 participating institutions were identified and case details extracted from the medical records. RESULTS: Case details of 3 horses and 4 ponies were available. Presenting complaints included weight loss despite good appetite in 4 animals, while in 3 hypertriglyceridaemia was identified incidentally. All animals were bright and alert and showed a normal or increased appetite. Serum triglyceride concentrations ranged from 10.5 to 60.3 mmol/l. Other abnormalities included hyperglycaemia in 6 animals, suspected insulin resistance and mild to severe increases in hepatic enzyme activities. In 2 animals, moderate hepatic lipidosis was confirmed histologically. Three horses and 3 ponies were diagnosed with pituitary pars intermedia dysfunction based on clinical signs and basal adrenocorticotropic hormone (ACTH) concentrations or dexamethasone suppression test results. In 5 of these, type 2 diabetes mellitus was also confirmed, while one pony suffered from type 2 diabetes mellitus without concurrent pituitary pars intermedia dysfunction. Laboratory abnormalities improved in 4 animals with treatment (pergolide and/or insulin), in one horse specific treatment was not attempted, and in 2 ponies treatment was impaired by the owner or only partly effective. In one of the latter cases, biochemical abnormalities persisted for 7 years without apparent ill effects. CONCLUSIONS AND POTENTIAL RELEVANCE: Horses and ponies may develop severe hypertriglyceridaemia secondary to endocrine disorders that are associated with insulin resistance. Hypertriglyceridaemia can resolve with treatment of the endocrinopathy. Although biochemical evidence of hepatic compromise was present, clinical abnormalities were not noted in these animals.

Ureteropyeloscopic anatomy of the renal pelvis of the horse.

REASONS FOR PERFORMING STUDY: Although the equine renal pelvis and terminal recesses have been described post mortem, little information exists about the endoscopic appearance of these structures in the living horse for guiding ureteropyeloscopy. OBJECTIVES: To further document the anatomy of the upper urinary collecting system, specifically the renal pelvis and terminal recesses, of the horse. STUDY DESIGN: Descriptive study of cadaver material. METHODS: Kidneys were harvested from 10 horses. Magnetic resonance imaging was performed after distension of the renal pelvis with an elastomer casting material, followed by visual inspection of corrosion casts. Transurethral ureteropyeloscopy of the upper urinary tract was performed in 4 horses, followed by histological and immunohistochemical examination of the renal medulla and pelvis of 3 animals. RESULTS: The equine renal pelvis was confirmed to be a funnel-shaped cavity, flattened dorsoventrally in the craniocaudal direction. Multiple papillary ducts (PDs) from the central part of the kidney open along a ∼3 cm long renal crest that protrudes into the renal pelvis, while PDs from each kidney pole open into 2 long (5-10 cm), narrow terminal recesses that terminate near either end of the renal crest. Openings of the terminal recesses narrow at their junction with the renal pelvis and could be visualised during ureteropyeloscopy in all horses. Minor anatomical variation of the renal crest and terminal recess openings was observed. CONCLUSIONS: Current endoscopic equipment can be used to visualise the renal pelvis but could not be advanced into the terminal recesses. The findings of this study will help guide future diagnostic and therapeutic ureteropyeloscopy.

Dysphagia associated with presumed pharyngeal dysfunction in 16 neonatal foals.

REASONS FOR PERFORMING STUDY: Dysphagia due to pharyngeal dysfunction occurs in human neonates and is associated with prematurity and hypoxic episodes. This syndrome probably occurs in neonatal foals but has not been reported. OBJECTIVES: The objectives of this study were to describe 1) a series of neonatal foals with dysphagia due to pharyngeal dysfunction; 2) the progression, treatment and resolution of the dysphagia; 3) the comorbidities; and 4) the prognosis for life and athleticism for affected foals. METHODS: Records from 3 referral equine hospitals were reviewed from neonatal foals with dysphagia of pharyngeal origin. Inclusion criteria were a normal to strong suckle, dysphagia evidenced by milk at the nostrils after nursing the dam, and endoscopic examination of the airway. Foals with mechanical reasons for dysphagia, botulism or hyperkalaemic periodic paralysis were not included. RESULTS: Sixteen neonatal foals qualified for the study. Eight (50%) were premature and/or diagnosed with hypoxic ischaemic encephalopathy. Twelve (75%) had aspiration pneumonia. Fifteen foals were discharged alive from the hospital, nursing the mare with no evidence of dysphagia (n = 14), or mild dysphagia (n = 1), a mean +/- s.d. of 7 +/- 6 days (median = 6.3 days, range 0-22 days) after hospital admission. One foal was subjectedto euthanasia in hospital. Follow-up nformation was available for 14 animals. Thirteen of 16 (81%) were alive and included one yearling and 12 horses >2 years old. Seven of the 14 (50%) were racing, training or in work, and 6 horses were pets, breeding animals or had unknown athletic status. Two had laryngeal deficits. One foal was subjected to euthanasia within weeks of discharge from the hospital due to aspiration pneumonia. CONCLUSION: Dysphagia related to pharyngeal dysfunction occurs in equine neonates and can resolve, but may require days to weeks of supportive care. Prognosis for life is favourable and for athleticism fair.

Diagnostic frequency, response to therapy, and long-term prognosis among horses and ponies with pituitary par intermedia dysfunction, 1993-2004.

BACKGROUND: Pituitary pars intermedia dysfunction (PPID) is common in older horses. OBJECTIVES: To determine diagnosis frequency, prognostic factors, long-term survival, and owner satisfaction with treatment. ANIMALS: Medical records from horses diagnosed with PPID, 1993-2004. METHODS: A retrospective cohort design with data collected from the Veterinary Medical Data Base (VMDB) and a cohort of 3 VTHs. Proportional accessions, annual incidence, and demographics were compared for all accessions. During the same period, a subset of medical records (n = 44) was extracted and owners (n = 34) contacted to obtain long-term follow-up information. RESULTS: Diagnoses of PPID were reported for 217 horses that presented to VTHs and were reported to the VMDB. Proportional diagnosis increased from 0.25/1,000 in 1993 to 3.72/1,000 in 2002. For 44 horses included in the follow-up study, the most commons signs were hirsutism (84%) and laminitis (50%). Of 34 horse owners contacted, the average time from onset of signs to diagnosis was 180 days. Improvement in ≥ 1 signs, 2 months after diagnosis, was reported by 9/22 (41%) of horse owners. Clinical signs and clinicopathologic data were not associated with survival, and 50% of horses were alive 4.6 years after diagnosis. Cause of death among horses (15/20; 85%) was euthanasia, and 11/15 (73%) were euthanized because of conditions associated with PPID. Most horse owners (28/29; 97%) said they would treat a second horse for PPID. CONCLUSION AND CLINICAL IMPORTANCE: PPID was diagnosed with increasing frequency, and 50% of horses survived 4.5 years after diagnosis. Owners were satisfied with their horses' quality of life and would treat a second horse if diagnosed.

Computed tomographic findings in the pituitary gland and brain of horses with pituitary pars intermedia dysfunction.

BACKGROUND: Pituitary pars intermedia dysfunction (PPID) is the most common endocrinologic disorder of aged horses. HYPOTHESIS/OBJECTIVES: Pituitary glands of PPID-affected horses are larger than those of aged horses without signs of PPID, and the size difference can be detected using computed tomography (CT) imaging. ANIMALS: Eight horses with clinical signs of PPID and supportive endocrinologic test results and 3 aged control (PPID-negative) horses. METHODS: Computed tomography examination of the brain and pituitary gland was performed twice in 10 of the 11 horses, approximately 6 months apart. Six PPID-affected horses were treated with pergolide for 6 months between CT scans. The second CT scan was followed by euthanasia and pathologic examination of 6 PPID-affected horses (4 treated horses). RESULTS: On initial examination, pituitary glands of PPID-affected horses were larger in height (P < .01) and width (P < .01) than controls, but the difference in length was not significant (P = .06). After 6 months of pergolide treatment of PPID-affected horses, pituitary gland length increased (P < .05), but height and width were not different from pretreatment values. There was no difference between pituitary gland measurements made at the terminal CT scans and necropsy. Furthermore, pituitary gland volume calculated from the measurements was highly correlated to pituitary gland weight. Additional CT findings were bilaterally symmetrical mineralization in the thalamus and cholesterol granulomas adjacent to the lateral and fourth ventricles. CONCLUSIONS AND CLINICAL IMPORTANCE: CT is a useful imaging modality to determine pituitary gland size of PPID-affected horses,and CT measurements are similar to gross pathologic measurements.

Suspect novel adverse drug reactions to trimethoprim-sulphonamide combinations in horses: a case series.

Adverse drug reactions to trimethoprim-sulphonamide combinations are common in many species, manifesting as gastrointestinal tract disorders, dermatopathies and blood dyscrasias. In this case series, neurological abnormalities in 4 horses being treated with trimethoprim-sulphonamide combinations at normal dosages and in one foal that received an overdose are described. The horses developed hypermetric gait, agitation and erratic behaviour. All signs resolved once medication was withdrawn, and no horse had residual deficits. No other cause for observed neurological deficits could be determined. These clinical signs appear to represent a novel adverse drug reaction to some commonly used antimicrobial combinations.

Neuroendocrine and non-neuroendocrine markers of inflammation associated with performance in endurance horses.

REASONS FOR PERFORMING STUDY: The inflammatory and neuroendocrine response to endurance exercise and relationship of these parameters to performance is not well documented in horses. HYPOTHESES OR OBJECTIVES: Evidence of systemic inflammation is associated with poor performance in horses competing in endurance events. METHODS: Blood was collected prior to and at the finish or elimination point from horses competing in both the 80 and 160 km American Endurance Ride National Championship competitions in 2006. Immunoreactive alpha-melanocyte stimulating hormone (α-MSH) and tumour necrosis factor-alpha (TNF-α) were quantified utilising radioimmunoassay (RIA) and enzyme-linked immunosorbent assay (ELISA) techniques, respectively. The concentration of total thiobarbituric acid reactive substances (TBARS) was measured fluorometrically. RESULTS: Thirty horses were included in the study. Endurance exercise was associated with a significant increase in TBARS in the 80 km group but not the 160 km group. TNF-α and α-MSH did not significantly change as a result of exercise in either distance group. Precompetition TBARS was significantly higher in horses that failed to finish the 80 km race, as well as when distances were combined. In addition, precompetition α-MSH was significantly lower in nonfinishers in the 160 km group. Furthermore, competition speed was positively correlated with precompetition α-MSH in the 80 km and negatively correlated with precompetition TNF-α when distances were combined. CONCLUSIONS: Our results suggest that basal oxidative stress markers, circulating cytokines and anti-inflammatory neuroendocrine hormones appear to correlate with endurance performance in horses. POTENTIAL RELEVANCE: Basal oxidative stress markers, circulating cytokines and anti-inflammatory neuroendocrine hormones may be predictive of athletic performance in endurance horses. Future studies evaluating the effect of training on these markers in endurance horses are warranted.

Sweat composition in Arabian horses performing endurance exercise on forage-based, low Na rations.

REASONS FOR PERFORMING STUDY: Excessive sweat loss during endurance exercise may lead to electrolyte disturbances and previous research suggests dietary factors may affect hydration status. While investigating the effect of dietary fibre type on hydration status, sweat samples were collected which allowed for the evaluation of sweat composition in horses consuming forage-based, low sodium (Na) rations. OBJECTIVE: To investigate sweat composition in Arabian horses performing endurance type exercise while fed forage-based, rations low in Na. METHODS: Six 2-year-old Arabian horses were fed, according to a replicated 3 × 3 Latin square, either grass hay (G), 50:50 grass hay:alfalfa hay (GA), or 50:50 grass hay: chopped fibres (GM) without any additional electrolyte supplementation. After 14 days on each diet, horses performed a 60 km treadmill exercise test. Sweat was collected from sealed pouches on the dorsal thorax after each of four 15 km exercise bouts. RESULTS: Intake (g/day) of Na (2.5 ± 0.4), Cl (72 ± 16), and Mg (18 ± 3) were not different between diets but K and Ca intakes (g/day) were greater (P < 0.05) on GA (246 ± 35; 101 ± 14) than G (176 ± 38; 59 ± 14) or GM (168 ± 33; 62 ± 15). There was no effect of diet on sweat pH (7.65 ± 0.04) or concentrations (mmol/l) of K (46 ± 3), Cl (133 ± 7), Ca (8.5 ± 1.1), or Mg (2.3 ± 0.3); yet diet did influence sweat Na concentration (P < 0.05, G 88 ± 5 mmol/l, GA 104 ± 5, GM 96 ± 6). Na and Cl concentrations were lower than those previously reported. CONCLUSIONS: Differences in sweat constituents due to diet were observed, but more importantly both Na and Cl concentration are lower than those previously reported perhaps due to low dietary Na intake or breed of animal.

Brown-headed cowbirds (Molothrus ater) harbor Sarcocystis neurona and act as intermediate hosts.

We tested the hypothesis that brown-headed cowbirds (Molothrus ater) harbor Sarcocystis neurona, the agent of equine protozoal myeloencephalitis (EPM), and act as intermediate hosts for this parasite. In summer 1999, wild caught brown-headed cowbirds were collected and necropsied to determine infection rate with Sarcocystis spp. by macroscopic inspection. Seven of 381 (1.8%) birds had grossly visible sarcocysts in leg muscles with none in breast muscles. Histopathology revealed two classes of sarcocysts in leg muscles, thin-walled and thick-walled suggesting two species. Electron microscopy showed that thick-walled cysts had characteristics of S. falcatula and thin-walled cysts had characteristics of S. neurona. Thereafter, several experiments were conducted to confirm that cowbirds had viable S. neurona that could be transmitted to an intermediate host and cause disease. Specific-pathogen-free opossums fed cowbird leg muscle that was enriched for muscle either with or without visible sarcocysts all shed high numbers of sporocysts by 4 weeks after infection, while the control opossum fed cowbird breast muscle was negative. These sporocysts were apparently of two size classes, 11.4+/-0.7 microm by 7.6+/-0.4 microm (n=25) and 12.6+/-0.6 microm by 8.0+/-0 microm (n=25). When these sporocysts were excysted and introduced into equine dermal cell tissue culture, schizogony occurred, most merozoites survived and replicated long term and merozoites sampled from the cultures with long-term growth were indistinguishable from known S. neurona isolates. A cowbird Sarcocystis isolate, Michigan Cowbird 1 (MICB1), derived from thin-walled sarcocysts from cowbirds that was passaged in SPF opossums and tissue culture went on to produce neurological disease in IFNgamma knockout mice indistinguishable from that of the positive control inoculated with S. neurona. This, together with the knowledge that S. falcatula does not cause lesions in IFNgamma knockout mice, showed that cowbird leg muscles had a Sarcocystis that fulfills the first aim of Koch's postulates to produce disease similar to S. neurona. Two molecular assays provided further support that both S. neurona and S. falcatula were present in cowbird leg muscles. In a blinded study, PCR-RFLP of RAPD-derived DNA designed to discriminate between S. neurona and S. falcatula showed that fresh sporocysts from the opossum feeding trial had both Sarcocystis species. Visible, thick-walled sarcocysts from cowbird leg muscle were positive for S. falcatula but not S. neurona; thin-walled sarcocysts typed as S. neurona. In 1999, DNA was extracted from leg muscles of 100 wild caught cowbirds and subjected to a PCR targeting an S. neurona specific sequence of the small subunit ribosomal RNA (SSU rRNA) gene. In control spiking experiments, this assay detected DNA from 10 S. neurona merozoites in 0.5g of muscle. In the 1999 experiment, 23 of 79 (29.1%) individual cowbird leg muscle samples were positive by this S. neurona-specific PCR. Finally, in June of 2000, 265 cowbird leg muscle samples were tested by histopathology for the presence of thick- and thin-walled sarcocysts. Seven percent (18/265) had only thick-walled sarcocysts, 0.8% (2/265) had only thin-walled sarcocysts and 1.9% (5/265) had both. The other half of these leg muscles when tested by PCR-RFLP of RAPD-derived DNA and SSU rRNA PCR showed a good correlation with histopathological results and the two molecular typing methods concurred; 9.8% (26/265) of cowbirds had sarcocysts in muscle, 7.9% (21/265) had S. falcatula sarcocysts, 1.1% (3/265) had S. neurona sarcocysts, and 0.8% (2/265) had both. These results show that some cowbirds have S. neurona as well as S. falcatula in their leg muscles and can act as intermediate hosts for both parasites.

Response to nasopharyngeal oxygen administration in horses with lung disease.

REASONS FOR PERFORMING STUDY: Guidelines for administration of oxygen to standing horses are unavailable because previous investigations of the efficacy of oxygen administration to increase arterial oxygenation in standing horses have produced equivocal results. OBJECTIVE: To determine the effect of nasal oxygen supplementation on inspired and arterial blood gas tensions in control horses and those with moderate to severe recurrent airway obstruction (RAO). METHODS: Normal horses (n = 6) and horses during an attack of RAO induced by stabling (n = 6) were studied. Oxygen was administered through either one or 2 cannulae, passed via the nares into the nasopharynx to the level of the medial canthus of each eye. Intratracheal inspired oxygen and carbon dioxide concentration and arterial blood gas tensions were measured at baseline and during delivery of 5, 10, 15, 20 and 30 l/min oxygen. RESULTS: Nasal cannulae and all but the highest oxygen flow rates were well tolerated. Fractional inspired oxygen concentration (F(I)O2) increased with flow but was significantly lower at all flow rates in horses with RAO compared with controls. Arterial oxygen tension (PaO2) was significantly increased (P < 0.001) by all flow rates, but was always lower in RAO-affected animals. At 30 l/min, PaO2 increased to 319 +/- 31 mmHg in control horses and 264 +/- 69 mmHg in horses with RAO. Additionally, a large arterial to end-tidal gradient for CO2 in RAO-affected horses was observed, indicating increased alveolar deadspace ventilation in these animals. CONCLUSIONS: The use of nasal cannulae to deliver oxygen effectively increases both F(I)O2 and PaO2 in horses with moderate to severe RAO. Oxygen flow rates up to 20 l/min are well tolerated, but flow rates of 30 l/min produce occasional coughing or gagging. POTENTIAL RELEVANCE: Oxygen therapy delivered by means of an intranasal cannula is a highly effective means of increasing arterial oxygen tension in horses with respiratory disease. Generally, flows of 10-20 l/min should be effective. If higher flows (20-30 l/min) are necessary, they should be delivered by means of 2 cannulae.

Genetic variation among isolates of Sarcocystis neurona, the agent of protozoal myeloencephalitis, as revealed by amplified fragment length polymorphism markers.

Sarcocystis neurona causes serious neurological disease in horses and other vertebrates in the Americas. Based on epidemiological data, this parasite has recently emerged. Here, the genetic diversity of Sarcocystis neurona was evaluated using the amplified fragment length polymorphism (AFLP) method. Fifteen S. neurona taxa from different regions collected over the last 10 years were used; six isolates were from clinically diseased horses, eight isolates were from wild-caught opossums (Didelphis virginiana), and one isolate was from a cowbird (Molothrus ater). Additionally, four outgroup taxa were also fingerprinted. Nine primer pairs were used to generate AFLP patterns, with a total number of amplified fragments ranging from 30 to 60, depending on the isolate and primers tested. Based on the presence/absence of amplified AFLP fragments and pairwise similarity values, all the S. neurona isolates tested were clustered in one monophyletic group. No significant correlation could be found between genomic similarity and host origin of the S. neurona isolates. AFLP revealed significant intraspecific genetic variations, and S. neurona appeared as a highly variable species. Furthermore, linkage disequilibrium analysis suggested that S. neurona populations within Michigan have an intermediate type of population structure that includes characteristics of both clonal and panamictic population structures. AFLP is a reliable molecular technique that has provided one of the most informative approaches to ascertain phylogenetic relationships in S. neurona and its closest relatives, allowing them to be clustered by relative similarity using band matching and unweighted pair group method with arithmetic mean analysis, which may be applicable to other related protozoal species.

Effects of oral electrolyte supplementation on endurance horses competing in 80 km rides.

REASONS FOR PERFORMING STUDY: There is no evidence that use of oral electrolyte pastes enhances performance in competing endurance horses. OBJECTIVE: To ascertain whether oral administration of a high dose (HD) of sodium chloride (NaCl) and potassium chloride (KCl) to endurance horses would differentially increase water intake, attenuate bodyweight (bwt) loss and improve performance when compared to a low dose (LD). METHODS: A randomised, blinded, crossover study was conducted on 8 horses participating in two 80 km rides (same course, 28 days apart). Thirty minutes before and at 40 km of the first ride 4, horses received orally 02 g NaCl/kg bwt and 0.07 g KCl/kg bwt. The other 4 received 0.07 g NaCl/kg bwt and 0.02 g KCl/kg bwt. Horses received the alternate treatment in the second ride. Data were analysed with 2-way ANOVA for repeated measures (P<0.05). RESULTS: Estimated water intake was significantly greater with HD both at the 40 km mark and as total water intake; however, differences in bwt loss and speed between HD and LD were not found. Treatment significantly affected serum Na+, Cl-, HCO3, pH and water intake, but not serum K+ or bwt. Serum Na+ and Cl- were significantly higher at 80 km when horses received HD, but no differences were found in early recovery. Venous HCO3- and pH were significantly lower throughout the ride and in early recovery when horses received HD. CONCLUSIONS AND POTENTIAL RELEVANCE: Other than enhancing water intake, supplementing endurance horses with high doses of NaCI and KCl did not provide any detectable competitive advantage in 80 km rides. Further, the elevated serum electrolyte concentrations induced with HD might not be appropriate for endurance horses.

Thyroid hormone responses to endurance exercise.

REASONS FOR PERFORMING STUDY: Limited information exists about changes in circulating thyroid hormone concentrations during prolonged endurance exercise in horses. OBJECTIVE: To examine the effects of prolonged exercise on serum iodothyronine concentrations in horses performing endurance exercise of varying distances. METHODS: Serum concentrations of iodothyronines were measured in horses before and after completion of 40, 56, 80 and 160 km endurance rides (Study 1); daily during a 5 day, 424 km endurance ride (Study 2); and before and for 72 h after completion of a treadmill exercise test simulating a 60 km endurance ride (Study 3). RESULTS: In Study 1, 40 and 56 km of endurance exercise had little effect on serum iodothyronine concentrations with the exception of a 10% decrease (P<0.05) in free thyroxine (FT4) concentration after the 56 km ride. In contrast, total thyroxine (T4), total triiodothyronine (T3), FT4 and free triiodothyronine (FT3) concentrations all decreased (P<0.05) after successful completion of 80 and 160 km rides, with decreases ranging from 13-31% and 47-54% for distances of 80 and 160 km, respectively. Further, pre-ride T4 concentration was lower (P<0.05) and FT3 concentration was higher (P<0.05) in horses competing 160 km as compared to horses competing over shorter distances. In Study 2, serum concentrations of T4, T3 and reverse triiodothyronine (rT3) progressively decreased (P<0.05) over the course of the multi-day ride. In Study 3, the greatest decrease (P<0.05) in all iodothyronines was observed at 12 h of recovery, ranging from 25% for FT4 to 53% for FT3, but all thyroid hormone concentrations had returned to the pre-exercise values by 24 h of recovery. CONCLUSION: Endurance exercise results in transient decreases in serum iodothyronine concentrations. POTENTIAL RELEVANCE: These data are important to consider when thyroid gland function is assessed by measurement of serum iodothyronine concentrations in endurance horses.

Changes in selected physiological and laboratory measurements in elite horses competing in a 160 km endurance ride.

REASON FOR PERFORMING STUDY: Limited information exists about the physiological changes and clinical problems that occur in elite horses competing in high-speed 160 km endurance races. OBJECTIVES: To provide initial data describing changes in physiological and laboratory measurements in horses competing in a high-speed, 160 km endurance race under temperate conditions and to compare data between horses that successfully completed the race and those that failed to finish. METHODS: Body mass (BM) was measured, blood samples were collected, and veterinary examinations performed on horses before, during, and at the finish of a CEI*** 160 km endurance race. RESULTS: Of 36 horses participating in the study, 22 (61%) completed the race. Twelve horses were eliminated for lameness and 2 for persistent heart rate elevation. Mean speed of finishers was 15.2 km/h. Mean +/- s.d. BM loss of finishers at the end of the race (5.7 +/- 2.6%) was not different (P = 0.58) from BM loss of nonfinishers at elimination (6.7 +/- 34%). Similarly, there were no significant differences in heart rate or veterinary assessment of hydration at the race end for finishers as compared to the elimination point for nonfinishers. PCV increased while sodium, chloride and potassium concentrations decreased with exercise but differences between finishers and nonfinishers were not detected. In contrast, both total and ionised calcium concentrations decreased in successful horses but remained unchanged in nonfinishers. CONCLUSIONS: Elite endurance horses are more likely to be eliminated from competition for lameness than metabolic problems; however, it remains unclear whether these conditions are entirely distinct. The magnitude of the decrease in sodium concentration in both finishers and nonfinishers was greater than in previous reports of 160 km rides. POTENTIAL RELEVANCE: These data should be of use for both organisers and participants in elite 160 km endurance races. The tendency toward hyponatraemia as well as the difference in calcium concentrations between finishers and nonfinishers warrant further study.