Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.

These-Université de Berne. / "Bibliographie": p. [63]-67.

No description available.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1995. / Vita. Abstract. Includes bibliographical references (leaves 138-158). Also available via the Internet.

Nonstructural carbohydrates (NSC), which includes sugars, starches and fructans in pasture forages, undergo circadian and seasonal variation which has direct effects on metabolism in grazing horses. Increased intake of NSC is implicated in the development of digestive and metabolic disorders, such as laminitis. A series of five studies at Virginia Tech's M.A.R.E. Center in April, May, August, and October 2005, and January 2006, examined circadian and seasonal variability in forage NSC content and metabolic and digestive variables in horses over a 36 h sampling period. Fourteen mares were randomly assigned to grazing (housed on a 5-ha predominantly tall fescue pasture; n = 10) or control (stabled within the pasture and fed timothy/alfalfa hay; n = 4) groups. Blood samples were collected hourly from the horses which corresponded to hourly pasture forage samples. In all five studies, plasma glucose and insulin were measured and proxies for insulin resistance were calculated. In the April study, plasma L-lactate and fecal pH, L-lactate, D-lactate and volatile fatty acids (VFAs) were also measured. Two approaches were used for the determination of carbohydrate profiles in pasture forage samples. For the first (LAB1), sugar was water soluble carbohydrates extracted prior to analysis for starch, and included fructans. The NSC was the sum of starch and sugar. For the second (LAB2), samples were analyzed for specific NSC fractions using hydrolytic enzymes, with the addition of HCL for the determination of fructans including graminans, the type of fructans in cool season grasses. Both the LAB1 and LAB2 analyses revealed circadian and seasonal patterns in forage NSC and its constituents. In general, pasture forage NSC content was lowest in the morning and highest in the late afternoon. April had the highest NSC content which was comprised mostly of simple sugars. Forage NSC content (LAB1) was associated with environmental variables in all months with strongest correlations in April; ambient temperature (r = 0.72, P < 0.001), solar radiation (r = 0.62, P < 0.001), and humidity (r = -0.84, P < 0.001). In the animals, plasma insulin was highest in grazing horses in April (P < 0.001) followed by May (P < 0.001). Plasma insulin was higher in grazing compared to control horses at all sample points in April, and a circadian pattern was evident (P = 0.012). In grazing horses, plasma glucose was higher in April than all months except for May, and plasma glucose was higher in grazing horses compared to controls in April. In grazing horses, plasma insulin was significantly correlated with NSC and sugar in April (r = 0.69 and r = 0.67, respectively); May (r = 0.46 and r = 0.47, respectively); and January (r = 0.44 and r = 0.46, respectively). In April only, individual mean insulin response was proportional to the increase in insulin per increase in unit of NSC (r2 = 0.033, P < 0.001). Sinusoidal circadian patterns in NSC (r2 = 0.51, P < 0.001) and insulin in grazing horses (r2 = 0.12, P < 0.001) had similar frequency (P = 0.36). Plasma L-lactate was higher in grazing horses (0.64 mmol/L) than control horses (0.40 mmol/L) (P < 0.001). Fecal pH was lower in grazing horses (pH 6.9) than control horses (pH 7.2) (P = 0.008). Fecal VFAs, including acetic acid, butyric acid, and D- and L-lactate were higher in grazing horses compared to control horses (P < 0.05). These studies identified a link between forage NSC content and alterations in carbohydrate metabolism and digestion that may increase risk of laminitis via exacerbation of insulin resistance. Strategies for management practices to decrease intakes of pasture NSC by horses at risk of developing metabolic disorders are needed. / Ph. D.

Forage is an essential part of the equine diet for health and performance. Pasture nonstructural carbohydrates (NSC) have been shown to fluctuate diurnally and seasonally throughout the year due to various factors including environmental conditions and plant stress. The intake of elevated NSC content is linked with metabolic and digestive diseases, including colic and laminitis. A yearlong grazing study was conducted at the Virginia Tech Middleburg Agricultural Research and Extension Center from October 2016 through September 2017 to investigate fluctuations in pasture NSC concentrations as well as the metabolic and digestive response of grazing horses. Twelve sporthorse mares (15 ± 3.4 yrs) were maintained on an 8.5-ha cool season mixed grass pasture with water, mineral (Buckeye Nutrition, Dalton, OH), and white salt ad libitum. Weekly pasture samples (200 g wet weight) were clipped at random 2.5 cm from the plant base at 0800 (AM) and 1600 h (PM) on d 1 and 0800 (AM) and 1300 h (PM) on d 2. Samples were weighed and dried at 70º C and submitted to a commercial laboratory (Equianalytical, Ithaca, NY) to determine NSC content (water soluble carbohydrates [WSC] + starch). Environmental conditions were measured including ambient temperature, relative humidity, solar radiation, rainfall, soil and canopy temperature, and photosynthetically active radiation (PAR). Corresponding weekly blood samples were collected at 1300 h on d 2 via jugular venipuncture into 4 mL potassium oxalate, and 7 mL EDTA vacutainer tubes and analyzed for glucose (mg/dL), insulin (μIU/mL), and L-lactate (mg/dL). Each month, fecal grab samples were collected from the midrectum to measure pH and Dlactate (µM). Additionally, monthly glucose and insulin dynamics (% ∆) were assessed via a modified oral sugar test. Pasture nutrients including DE (2.35 ± 0.12 Mcal/kg), NSC (25.45 ± 4.02% DM), WSC (19.65 ± 3.47% DM), and starch (7.25 ± 1.29% DM) were higher in the afternoon hours (PM) compared to morning measurements (AM). Pasture CP and carbohydrate fractions were higher in the spring and fall months compared to summer and winter months with NSC concentrations being highest in May (wk 19) at 25.45% DM. Pasture NSC content was correlated (P ≤ 0.05) with relative humidity (r = 0.38), solar radiation (r = 0.32), and PAR (r = 0.51) and tended (P ≤ 0.1) to have a relationship with ambient temperature (r = 0.23) and rainfall (r = 0.23). There was seasonal variation in all morphometric measures in grazing horses. BW was highest in the spring (P < 0.0001), while BCS and CNS were highest in the fall (P = 0.0021 and P < 0.0001, respectively). Metabolic responses in grazing horses also fluctuated seasonally with glucose and insulin concentrations being most elevated in the spring (P < 0.0001). There was also seasonal variation in digestive measures in grazing horses. Plasma Llactate and fecal D-lactate means differed by month (P < 0.05) with the highest concentrations in April (11.8 ± 0.91 mg/dL and 4220.4 ± 185.5 µM, respectively). Fecal pH was most acidic in April (6.52 ± 0.08). Pasture NSC content was correlated with weight (r = 0.35), glucose (r = 0.21), and insulin (0.26) in grazing horses and tended to have a relationship with CNS (r = 0.14). There was also a relationship between NSC and plasma L-lactate (r = 0.33), fecal D-lactate (r = 0.48) and pH (r = -0.27). Lastly, glucose and insulin % ∆ (P < 0.0001) were greatest during spring months, but there was no effect of fasting insulin (P < 0.2787) or fasting glucose (P < 0.2055) on glucose % ∆. These data indicate a relationship between seasonal changes in pasture NSC content and the physiological response in grazing horses. Future aims include evaluating possible seasonal fluctuations in the hindgut microbiome of grazing horses to better understand the link between the equine microbiome and nutritionally-related disturbances. Improved grazing management strategies are needed to reduce the risk of metabolic and gastrointestinal disorders in horses, which may lead to subsequent colic and pasture associated laminitis. / Doctor of Philosophy / Lush pastures are an important part of the equine diet for overall health and performance. However, there are several nutrition-related diseases that can occur when environmental conditions favor starch and sugar (nonstructural carbohydrates, NSC) accumulation in pasture grasses. Environmental conditions such as air temperature, intensity of sunlight, frost, and drought can all lead to increased accumulation of NSC in pasture grasses, especially in spring and fall months. When horses graze pastures with elevated NSC concentrations they can develop several conditions such as obesity, insulin resistance, and gastrointestinal upset. One of the most common but least understood equine diseases is pasture-associated laminitis, in which inflammation causes pain and damage to the structure of the equine hoof. The objectives of our research were to measure seasonal changes in pasture NSC concentrations as well as the metabolic and digestive response in grazing horses to better understand how the intake of pasture NSC content may lead to disturbances or disease in the horse. A yearlong grazing study was conducted at the Virginia Tech Middleburg Agricultural Research and Extension Center from October 2016 through September 2017 to investigate the relationship between pasture NSC and grazing horses. Twelve sporthorse mares were maintained on a 21-acre mixed grass pasture with water, mineral (Buckeye Nutrition, Dalton, OH), and white salt ad libitum. Weekly pasture samples collected to determine NSC content of the grasses. Weekly blood samples were collected from the horses to measure glucose, insulin, and L- lactate concentrations. Each month, fecal samples were collected to measure pH and Dlactate. Additionally, monthly glucose and insulin dynamics (% ∆) were assessed via a modified oral sugar test. Pasture NSC content fluctuated throughout the year and was most elevated in the spring and fall months. There was seasonal variation in the metabolic response of grazing horses with glucose and insulin concentrations being highest in the spring months. There was also seasonal variation in digestive measures in grazing horses. Plasma L-lactate and fecal D-lactate were most elevated in the spring and fecal pH was most acidic in the spring. These results indicate a relationship between seasonal changes in pasture NSC content and the physiological response in grazing horses. Future aims include evaluating possible seasonal fluctuations in the hindgut microbiota of grazing horses to better understand the link between the equine gastrointestinal bacteria and nutritionally-related diseases. Improved grazing management strategies are needed to reduce the risk of metabolic and gastrointestinal disorders in horses, which may lead to diseases such as colic and pasture-associated laminitis.

Chronic neuropathic pain, resulting from dysfunction of the nervous system, is a clinical concern in both humans and animal patients. Neuropathic pain is characterised by spontaneous pain, hypersensitivity, manifested as hyperalgesia and allodynia, and refractoriness to conventional analgesics such as non-steroidal anti-inflammatory drugs, thus representing an unmet therapeutic need. Equine laminitis is a disease that involves the disruption of the dermoepidermal junction within the hoof, leading to severe pain and lameness, with poor responsiveness to anti-inflammatory therapy. We developed a Quantitative Sensory Testing method, using a novel hydraulically-powered feedbackcontrolled hoof tester, in order to provide an objective tool for the assessment of mechanical hyperalgesia in laminitic horses. Hoof Compression Thresholds of laminitic horses were significantly lower than those of normal horses and variance component analysis of the data confirmed the reliability of the method. In order to investigate mechanisms underlying laminitis pain, we performed histological studies of peripheral nerves innervating the hoof. Electron micrographic analysis of the digital nerve of laminitic horses revealed a significant reduction in the number of unmyelinated and myelinated fibres together with abnormal morphology. Additionally, cell bodies of sensory neurons innervating the hoof in cervical C8 dorsal root ganglia showed an upregulated expression of the nerve injury marker activating transcription factor-3 (ATF3), neuropeptide Y (NPY), and the TRPM8 channel; each of which has been associated with laboratory models of neuropathic pain. Previous work has shown that, in a rodent model of neuropathic pain, the TRPM8 channel is upregulated in sensory neurons and its activation by cool temperature, menthol or icilin leads to reversal of the hypersensitive pain state. Further investigation of TRPM8-channel mediated analgesia was aimed at uncovering the molecular mechanisms involved in the activation of this system in sensitised states. It was hypothesised that serotonin, released following inflammation and nerve damage, can enhance TRPM8 channel activity through peripheral 5-HT1B receptors. Calcium fluorometry carried out in HEK293 cells transfected with the TRPM8 channel and the 5-HT1B receptor revealed that coadministration of a 5-HT1B receptor agonist facilitated the activation of the TRPM8 channel by icilin. Moreover, it appears that this effect is mediated through phospholipase D1 (PLD1), possibly leading to increased production of phosphatidylinositol (4,5-) bisphosphate (PIP2), a known positive modulator of TRPM8 channel activity. In vitro co-immunoprecipitation studies suggested that the TRPM8 channel, the 5-HT1B receptor and PLD1 physically interact with each other, further providing a molecular basis for their functional co-operation. Calcium imaging carried out in cultured rat DRG cells showed that the 5-HT1B receptor-mediated enhancement of icilin responses at the TRPM8 channel also occurs in sensory cells and is reversed by inhibition of PLD1. Moreover, TRPM8 and the 5-HT1B receptor appear to be physically associated in vivo as shown by their co-immunoprecipitation from spinal cord homogenates. Assessment of nociceptive behavioural reflexes following intrathecal injection of selective pharmacological agents provided further support for the idea of 5-HT1B receptor facilitation of TRPM8 channel responses in vivo. In addition to providing novel evidence of a neuropathic component to equine laminitis and validation of a novel QST method for pain assessment in horses, this study reveals for the first time a physical and functional interaction between the 5-HT1B receptor and the TRPM8 channel.

No description available.

Memoria para optar al Título Profesional de Médico Veterinario / El síndrome metabólico equino (SME) se puede definir como una agrupación de factores de riesgo, asociados a desregulación endocrina y metabólica, que predicen un mayor riesgo de laminitis. Hoy en día, se reconoce que las causas endocrinas de laminitis, principalmente SME y disfunción de la pars intermedia, son las principales razones de presentación de éste signo clínico en la práctica equina. La principal utilidad de comprender la fisiopatología y el concepto de laminitis endocrina, es crear un enfoque dirigido a sus causas, con el objetivo de que se puedan tomar medidas preventivas para reducir su incidencia, en lugar de simplemente actuar frente a los casos después de que hayan demostrado signología clínica avanzada. A pesar del énfasis inicial que se dio a la resistencia a insulina (RI) como principal causal de este tipo de laminitis, estudios recientes han indicado que la hiperinsulinemia e hiperglicemia resultante de la RI son las responsables y no así, a la resistencia del tejido del casco a esta hormona. Por lo tanto, una predisposición a hiperinsulinemia sin previo consumo de alimento, puede predecir con frecuencia la susceptibilidad a la laminitis. Aunque todos los individuos experimenten una hiperinsulinemia post prandial, ésta puede magnificarse o manifestarse en ayunas en presencia de ciertos factores como el exceso de adiposidad regional, raza, falta de ejercicio físico, edad y sexo. Específicamente, la presencia de obesidad, además de la insulina en exceso, puede ser indicativo de SME y la desatención a su control podría resultar en un mayor riesgo de laminitis. Para diagnosticar un ejemplar con este síndrome, se describe que es necesario complementar el examen físico con pruebas de laboratorio que identifiquen la hiperinsulinemia e hiperglicemia. Dentro de los exámenes ya existentes para este propósito, estudios recomiendan que se realicen mediciones basales y dinámicas a la vez, ya que los resultados de una sola prueba pueden ser inconcluyentes para este propósito. Una buena estrategia de control de estas alteraciones endocrinas comprende un manejo dietario y ejercicios rutinarios, los cuales, en ciertos casos, pueden ser complementados con un tratamiento farmacológico, basado en la utilización de Metformina y Levotiroxina, medicamentos que han demostrado tener buenos resultados en la regulación de insulina y glucosa en sangre en esta especie. / Equine metabolic syndrome (EMS) can be defined as a group of risk factors, associated with endocrine and metabolic dysregulation, that predict an increased risk of laminitis. Today, it is recognized that the endocrine causes of laminitis, mainly EMS and the pars intermedia dysfunction, are the main reasons for presenting this clinical sign in equine practice. The main usefulness of understanding the pathophysiology and the concept of endocrine laminitis, is to create an approach directed to its causes, with the objective that preventive measures can be taken to reduce its incidence, instead of simply acting in front of cases after have shown advanced clinical signology. Despite the initial emphasis on insulin resistance (IR) as the main cause of this type of laminitis, recent studies have indicated that the hyperinsulinemia and hyperglycemia resulting from IR are responsible, and not the resistance of the hoof tissue to this hormone. Therefore, a predisposition to hyperinsulinemia without prior feed intake can often predict susceptibility to laminitis. Although all individuals experience post-prandial hyperinsulinemia, it can be magnified or manifested during fasting in the presence of certain factors such as excess regional adiposity, race, lack of physical exercise, age and sex. Specifically, the presence of obesity, in addition to excess insulin and glucose, may be indicative of EMS and neglecting their control could result in an increased risk of laminitis. To diagnose a specimen with this syndrome, it is described as necessary to complement the physical examination with laboratory tests that identify hyperinsulinemia and hyperglycemia. Among the existing tests for this purpose, studies recommend that baseline and dynamic measurements of these to be taken at the same time, since the results of a single test may be inconclusive for this purpose. A good strategy to control these endocrine alterations includes a dietary management and routine exercises, which, in certain cases, because of pain in the foot region due to laminitis, can be complemented with a pharmacological treatment, based on the use of Metformin and Levothyroxine, which have shown good results in the regulation of blood insulin and glucose in this species.

Glucose and lipid metabolism are dysregulated in obese horses. Altered glucose metabolism is evidenced by the development of insulin resistance and increased fasting plasma insulin concentrations (hyperinsulinemia) while altered lipid metabolism is evidenced by increased plasma lipid concentrations. Obesity in horses also increases the risk of the painful hoof disease, laminitis. Three experiments were performed to investigate the regulation of nutrient metabolism in skeletal muscle and adipose tissue of lean, healthy horses. Adipose tissue was found to be the primary lipogenic tissue of horses, with acetate being the primary lipogenic substrate. Secondly, ten, lean horses were used to investigate the effects of acute hyperinsulinemia on nutrient metabolism. Increasing plasma insulin concentrations to >1,000 mIU/L for six hours decreased transcript abundance of glucose transporters and the insulin receptor in adipose tissue, and decreased protein abundance of the insulin receptor in skeletal muscle, potentially indicating that hyperinsulinemia potentiates insulin resistance. Insulin infusion also reduced mRNA abundance of lipid transporters in adipose tissue while increasing them in skeletal muscle. The final experiment investigated the influence of the insulin-sensitizing drug, pioglitazone, and lipopolysaccharide, on nutrient metabolism in skeletal muscle and adipose tissue, and their association with insulin sensitivity. Pioglitazone treatment did not increase insulin sensitivity; however it did increase skeletal muscle transcript abundance of the insulin receptor and the non-insulin sensitive glucose transporter and adipose tissue protein abundance of the insulin-sensitive glucose transporter (GLUT4). Lipopolysaccharide decreased insulin sensitivity regardless of pioglitazone pre-treatment, which was associated with decreased transcript abundance of GLUT4 in skeletal muscle and adipose tissue of untreated horses, but not adipose tissue of pioglitazone treated horses. / Ph. D.