The effect of insulin infusion on heart rate and systemic blood pressure in horses with equine metabolic syndrome.

BACKGROUND: There is little evidence that horses with equine metabolic syndrome (EMS) have higher resting blood pressures than horses with normal insulin sensitivity. However, there are indications that EMS horses have an altered dynamic response to the cardiovascular effects of insulin. OBJECTIVES: To examine heart rate and the systemic blood pressure response in EMS and control horses during insulin infusion. STUDY DESIGN: Cross-sectional study. METHODS: Horses were examined with an oral sugar test (OST) and a euglycaemic hyperinsulinaemic clamp (EHC). Based on the results from the OST, the horses were classified as either EMS or control. Blood pressure was measured before the start of the EHC and at 60, 120 and 180 min of the EHC. RESULTS: There were 16 EMS and 12 control horses. Mean resting heart rate was higher for EMS horses compared with control (35.6 ± 5.1 vs. 30.3 ± 3.5 beats/min). Systolic, diastolic and mean arterial blood pressure did not differ between groups at the start of the EHC. Blood pressure decreased gradually during the EHC in the control group, whereas the EMS group showed no decline in systolic, diastolic or mean arterial pressure. MAIN LIMITATIONS: Limited number of horses. CONCLUSIONS: Horses with EMS have cardiovascular changes that affect resting heart rate and systemic blood pressure during insulin infusion.

Evaluation of glucose and insulin response to haylage diets with different content of nonstructural carbohydrates in 2 breeds of horses.

Information about the effect of nonstructural carbohydrates (NSCs) in forage on the postprandial glucose and insulin response in horses is scarce. This is of interest as postprandial hyperinsulinemia in horses is a risk factor for laminitis. In addition, insulin sensitivity (IS) differs between breeds. The aim was to evaluate the postprandial glucose and insulin response to haylage diets with different NSC content in horses of 2 different breeds and to evaluate the relationship between the postprandial insulin response and measures of IS derived from a frequently sampled intravenous glucose tolerance test (FSIGTT). Standardbreds (n = 9) and Icelandic horses (n = 9) with a mean body condition score of 5.5 ± 0.6 (scale 1-9) were studied. Horses were clinically healthy at the start of the study and had no history of endocrinopathic laminitis. The experiment was conducted as a replicate 3 × 3 Latin square, in which horses were fed haylage diets with low (4.2%), medium (13.6%), and high (18.2%) NSC content of dry matter. Blood sampling was performed before feeding and every 30 min until 300 min after feeding. An FSIGTT was also performed in all horses. The early (first 60 min) and the total (300 min) postprandial glucose and insulin response (area under the curve [AUC]) was higher after a meal of both medium and high NSC haylage in comparison with low NSC haylage when both breeds were combined (P ≤ 0.02). There was a main effect of breed for the early (P ≤ 0.004) but not for the total (P > 0.12) postprandial glucose and insulin response. The IS index was comparable between breeds (P = 0.75). The natural logarithm of the peak concentration, the AUC for the first 60 min and the total AUC for insulin, after a meal of medium and high NSC haylage, were moderately negatively correlated (P < 0.02; r = -0.55 to -0.72) with the natural logarithm of IS index from the FSIGTT. This relationship was not evident for haylage with low NSC content (P > 0.054). This study demonstrates that the postprandial insulin response is affected by both the NSC content of haylage and the horse's IS. However, the impact of IS was diminished when the NSC content in haylage was low (4.2% of dry matter).

Relationship Between ß-cell Response and Insulin Sensitivity in Horses based on the Oral Sugar Test and the Euglycemic Hyperinsulinemic Clamp.

BACKGROUND: A hyperbolic relationship between ß-cell response and insulin sensitivity (IS) has been described in several species including rodents, dogs, and humans. This relationship has not been elucidated in the horse. HYPOTHESIS/OBJECTIVES: To determine whether the hyperbolic relationship between ß-cell response and IS exists in horses by using indices of ß-cell response from the oral sugar test (OST) and IS measurements from the euglycemic hyperinsulinemic clamp (EHC). A second aim was to compare how well IS estimates from the OST and EHC correlate. ANIMALS: Forty-nine horses with different degrees of insulin regulation (normal-to-severe insulin dysregulation). METHODS: Cross-sectional study. Horses were examined with an OST and an EHC. RESULTS: Decreased IS was associated with increased ß-cell response in the horses. Nine of 12 comparisons between indices of ß-cell response and IS measures fulfilled the criteria for a hyperbolic relationship. Indices of IS calculated from the OST correlated highly with the insulin-dependent glucose disposal rate (M) and the insulin-dependent glucose disposal rate per unit of insulin (M/I) determined from the EHC (r = 0.81-0.87). CONCLUSIONS AND CLINICAL IMPORTANCE: A hyperbolic relationship between ß-cell response and IS exists in horses, which suggest that horses with insulin dysregulation respond not only with postprandial hyperinsulinemia but are also insulin resistant. The OST is primarily a test for ß-cell response rather than a test for IS, but calculated indices of IS from the OST may be useful to estimate IS in horses, especially when the horse is insulin resistant.

Serum thymidine kinase activity in clinically healthy and diseased horses: a potential marker for lymphoma.

Serum thymidine kinase (sTK) activity is a tumour marker used as a prognostic indicator for lymphoma in humans, dogs and cats. The aim of this study was to evaluate the clinical utility of sTK as a biomarker for lymphoma in horses. Serum samples were collected from clinically normal horses (n = 37), horses with lymphoma (n = 23), horses with non-haematopoietic neoplasia (n = 9) and horses with inflammatory disease (n = 14). sTK was measured using a radioenzyme assay. A reference cut-off value of <2.7 U/L (mean + 2 standard deviations, SDs) was established using data from clinically normal horses. sTK activity (mean ± SD) was 26.3 ± 91.5 U/L (range 0.8-443 U/L) for horses with lymphoma, 2.3 ± 1.4 U/L (range 0.6-5.7 U/L) for horses with non-haematopoietic neoplasia and 1.5 ± 0.6 U/L (range 0.6-2.8 U/L) for horses with inflammatory disease. Horses with lymphoma had significantly higher sTK activity than horses without clinical signs of disease (P <0.01), horses with inflammatory disease (P <0.01) and horses with non-haematopoietic neoplasia (P <0.05). sTK activity is a potentially useful biomarker for equine lymphoma.

Variation in training regimens in professional showjumping yards.

REASONS FOR PERFORMING STUDY: Training regimens of showjumping horses under field conditions are largely undocumented. OBJECTIVES: The aims of this study were to quantify and compare training regimens used in professional-level showjumping yards, with respect to time exercised and type of activity. STUDY DESIGN: Prospective cohort study. METHODS: A prospective 6-month cohort study of showjumping horses in 4 European countries (The Netherlands, Sweden, Switzerland, Great Britain) was designed to analyse training and health data, in yards with several horses in training and riders competing at professional level. Riders documented the daily frequency and duration of all physical activities of the horses. Variation in training routines were compared between riders, location and time. Mixed-models analysis was used to examine factors associated with total time exercised and time spent in flatwork. RESULTS: In 4 countries, the 31 participating riders trained 263 European Warmbloods. The total days at risk (e.g. days in which the horses were considered fit for exercise) was 39,262. Mean time spent in daily exercise, including ridden work, lungeing and treadmill exercise, varied between riders from 19-52 min/day at risk. There was considerable variation in activities and level of heavy work and light exercise, i.e. turnout. Total time exercised and time spent in flatwork differed with month, country and proportion of days lost to training. Low variation of activities was associated with decreased total time trained and increased time spent in flatwork. CONCLUSIONS: Riders at this elite professional level of showjumping used training regimens that vary substantially in time spent training and other physical activities and showjumping horses are challenged differently during training despite competing at the same level. Whether all training regimens prepare the horses equally for the demands of competition remains to be determined.

Repeatability of the combined glucose-insulin tolerance test and the effect of a stressor before testing in horses of 2 breeds.

BACKGROUND: The increasing number of horses diagnosed with insulin resistance (IR) and the suggested link between IR and laminitis has highlighted the need to accurately diagnose IR in clinical practice. HYPOTHESIS/OBJECTIVES: The aim of the study was to evaluate the repeatability of the combined glucose-insulin tolerance test (CGIT) as well as to determine the effect of 2 different breeds and the effect of a stressor on the test results. ANIMALS: Clinically normal horses, 9 Standardbred horses and 9 Icelandic horses. METHODS: Prospective clinical nonrandomized trial. The CGIT was performed on all horses on 2 occasions 3 weeks apart. An additional CGIT was performed on four of the Standardbred and four of the Icelandic horses after transportation to a new environment (stressor) the day before testing. RESULTS: Calculated parameters for the glucose curve of the CGIT had low repeatability, whereas the parameters for the insulin curve had high repeatability. There was an effect of breed (Standarbred versus Icelandic horse) as well as stress on the glucose dynamics, but not on the insulin dynamics of the CGIT. CONCLUSION AND CLINICAL IMPORTANCE: Repeatability of the glucose dynamics of the CGIT is low. In addition, there appears to be breed differences in the glucose dynamics. It is therefore suggested that diagnosis of IR should not be made solely based on results from the glucose curve of the CGIT.

Expression of tlr4, md2 and cd14 in equine blood leukocytes during endotoxin infusion and in intestinal tissues from healthy horses.

The expression of tlr4, md2 and cd14 was studied in equine blood leukocytes and in intestinal samples using real time PCR. The stability of three commonly used reference genes, glyceraldehyde-3P-dehydrogenase (GAPDH), hypoxantine ribosyltransferase (HPRT) and succinate dehydrogenase complex subunit A (SDHA), was evaluated using qbase(PLUS). The equine peripheral blood mononuclear cells (eqPBMC) examined were either stimulated in vitro with Phorbol 12-myristate 13-acetate (PMA) and ionomycin or with the CpG oligodeoxynuclotide 2216 (CpG-ODN 2216) or obtained from horses before, during and after infusion of endotoxin. Intestinal tissue from healthy horses was sampled at ileum, right dorsal colon and rectum. Ranking of the three reference genes used for normalisation identified the combination HPRT/SDHA as most suitable both when determined ex vivo in leukocytes obtained from experimentally induced endotoxaemia and in eqPBMC activated in vitro while HPRT/GAPDH were most appropriate for the intestinal samples. The relative amounts of mRNA for TLR4 and MD-2 increased threefold during in vitro activation of the cells with CpG-ODN 2216 but was decreased in cultures stimulated with PMA/ionomycin. A transient elevation in the transcription of tlr4 and md2 was also evident for equine blood leukocytes following endotoxaemia. The levels of mRNA for CD14 on the other hand remained unaffected both during the induction of endotoxaemia and in the in vitro stimulated PBMCs. A low steady expression of TLR4, MD-2 and CD14 mRNA was demonstrated for the intestinal samples with no variation between the intestinal segments analysed. Thus, the foundation for real time PCR based levels of analysis of mRNA for all three components in the equine LPS receptor complex in different intestinal segments was set, making it possible to carry out future expression studies on clinical material.

The physiological responses to simulated race tests on a track and on a treadmill in standardbred trotters.

REASON FOR PERFORMING STUDY: It is unclear to what extent the physiological response to a standardised treadmill exercise test simulating racing conditions resembles the circulatory and metabolic response observed after a simulated race on a track. OBJECTIVES: To compare the physiological responses of a standardised treadmill exercise test used to simulate racing conditions and a simulated race performed on a track on the same Standardbred trotting horses, all in racing condition. METHODS: Six Standardbred trotters in racing condition performed a standardised inclined treadmill exercise test protocol simulating racing conditions (ST) and a simulated race on a field track (FT). Heart and respiratory rates, haemoglobin, packed cell volume (PCV), glucose, pH, total carbon dioxide and potassium in venous blood and plasma lactate and total plasma protein were measured before and immediately after exercise and during recovery. RESULTS: No differences were observed in heart rate, haemoglobin, PCV, total plasma protein, glucose concentrations after exercise and during recovery between the tests. Plasma lactate was higher and total carbon dioxide concentrations and pH were lower in blood at the end of exercise in the FT compared to the ST. Plasma lactate concentrations were still higher 30 min post exercise in the FT compared to the ST. Blood pH returned to resting values at 15 min of recovery for the ST and at 60 min of recovery for the FT. At 60 min of recovery total carbon dioxide concentrations had still not returned to resting values in any of the tests. Respiratory rate at the end of exercise and body temperature at 15 min of recovery was higher after the ST than the FT. Exercise caused an increase in blood potassium concentrations at the end of exercise in both tests, but concentrations were lower after the FT compared to the ST. CONCLUSIONS: The haemodynamic response to the ST test at the end of exercise and during recovery, assessed from heart rate, Hb, and PCV, was similar to the response observed in the FT test. The differences observed in plasma lactate, blood pH and TCO2 concentrations between the ST and FT show that anaerobic metabolism was greater in the FT as this test included a finish at maximal speeds. POTENTIAL RELEVANCE: The treadmill test used in this study to simulate a race resembles the haemodynamic response but not the anaerobic metabolic response observed after a simulated race on a track.

Effects on exercise response, fluid and acid-base balance of protein intake from forage-only diets in standardbred horses.

REASON FOR PERFORMING STUDY: High-energy forage might be an alternative to concentrates for performance horses and such forage can be produced by an early cut. However, early cut forage is high in crude protein (CP), which may result in an excessive CP intake. OBJECTIVES: To investigate how CP intake affects nitrogen (N), fluid and acid-base balance, and exercise response in horses fed high-energy forage diets. The hypothesis was that high CP intake causes acidosis, and alters fluid balance and response to intensive exercise. METHODS: Two forage-only diets based on high-energy grass forage were fed for 23 days in a crossover design to 6 Standardbred horses in racing condition. One forage diet provided a high (HP) CP (16.6%) intake and the other diet provided recommended intake (RP) of CP (12.5%) for racehorses. The horses had intensive exercise twice and slow exercise 1-3 times every week. At the beginning and end of each period, faeces and urine were collected for 48 and 72 h, respectively and analysed for dry matter, pH and N content. At Days 19 and 23 in each period 2 race-like exercise tests were performed, a standardised treadmill test and a field test on a race track. Blood samples were taken before, during and after the tests and analysed for sodium (Na), potassium (K), chloride (CI), total plasma proteins (TPP), TCO2, urea, pH and lactate. The strong ion difference (SID) was calculated and heart rate and respiratory rate was also recorded. RESULTS: There was a decrease in urinary pH and an increase in N excretion, blood urea, water intake, urine volume and faecal water content on the HP diet. Total water intake was higher than the increase in urinary and faecal water loss indicating increased evaporative losses on the HP diet. During the exercise tests there were no significant differences between diets in TPP, plasma lactate, blood Na, K, Cl, TCO2, pH, SID and respiratory or heart rates. CONCLUSION: Feeding a forage-only diet with a CP intake corresponding to 160% of the requirement caused an increase in N excretion within 36-48 h after the diet was introduced and alterations in fluid and acid base balance at rest. POTENTIAL RELEVANCE: The increased urine and probably also evaporative fluid losses suggest that feeding a HP diet will cause an unnecessary challenge for horses during prolonged exercise.