Equine metabolism encompasses the biochemical processes that occur within horses to maintain life, including the conversion of food into energy, the synthesis of necessary compounds, and the elimination of waste products. These processes are essential for supporting various physiological functions such as growth, reproduction, and physical performance. Key components of equine metabolism include carbohydrate, fat, and protein metabolism, each of which contributes to the overall energy balance and health of the horse. Factors influencing metabolic rate and efficiency in horses include age, breed, diet, exercise, and health status. This page compiles peer-reviewed research studies and scholarly articles that explore the mechanisms, regulation, and implications of metabolic processes in equine physiology.
Räsänen LA, Myllymäki T, Hyyppä S, Maisi P, Pösö AR.Plasma concentrations of hypoxanthine, uric acid, and allantoin, which are breakdown products of adenine nucleotides, were measured in Standardbred and Finnhorse trotters during and after an exercise test on a high-speed treadmill, after an incremental exercise test performed on a racetrack, and after a racing competition. Fiber-type composition of the middle gluteal muscle and the muscle concentrations of adenine nucleotides and inosine monophosphate were measured after the racetrack test. Changes in the concentration of hypoxanthine were not observed in any of the tests. Peak concentration o...
Puigdemont A, Ramis J, Guitart R, Arboix M.Usually, smaller mammals have higher clearances per unit body mass than do larger mammalian species. When clearance and other pharmacokinetic parameters are correlated with internal physiological processes, species tend to dispose of drugs at a similar pace. The first application of this concept is pharmacokinetic time, expressed with different units: Kallynochron, Apolysichron, Dienetichron, and Syndesichron. The present work describes pharmacokinetic time in these units from data obtained with propafenone in eight animal species: mouse, rat, rabbit, dog, sheep, human, cow, and horse. Additio...
Pösö AR, Essén-Gustavsson B, Persson SG.Plasma concentrations of lactate, amino acids, ammonia and products of purine catabolism were studied before, during and after a standardised incremental exercise test in 29 Standardbred trotters admitted to the clinic for exercise tolerance testing. According to their red cell volume the horses were divided into red cell normovolaemic and red cell hypervolaemic (polycythaemic) groups. The exercise-response curve for taurine differed significantly in the two groups, whereas all the other amino acids behaved similarly. The [branched-chain amino acid]/[alanine] ratio, a proposed indicator for th...
Seay SS, Aucoin DP, Tyczkowska KL.A simple, rapid and sensitive high-performance liquid chromatographic procedure has been developed for the determination of ketamine and dehydronorketamine in equine serum. Sample preparation consisted of mixing equal volumes of serum and acetonitrile-phosphoric acid (85%)-water (20:2:78, v/v/v), followed by ultrafiltration through a 10,000 molecular mass cut-off filter. Separation of these two analytes in the ultrafiltrate was accomplished on a reversed-phase phenyl column eluted with methanol-acetonitrile-phosphate buffer solution. Ketamine and dehydronorketamine were detected by a variable ...
Rivero JL, Serrano AL, Henckel P, Agüera E.Triplicate biopsies from three different depths of the gluteus medius muscle were obtained in 36 endurance-raced horses, aged 8.42 +/- 2.85 yr. Twenty of the horses were considered excellent endurance performers according to the mean speed of their three fastest records in endurance events for the past 2 or 3 years, whereas 16 were moderate performers, with a mean racing speed < 12.5 km/h (in 120- to 180-km endurance rides), < 14 km/h (in 80- to 120-km endurance rides), or < 13.5 km/h (in 40- to 60-km endurance rides). Significant differences in muscle fiber type composition and fiber size wer...
Watson TD, Packard CJ, Shepherd J.1. Equine plasma contains lipoproteins corresponding to very low density (VLDL), low density (LDL) and high density lipoproteins (HDL). 2. HDL accounts for approximately 60% of plasma lipoprotein mass and consists of a single population of particles. 3. LDL is heterogeneous comprising three discrete subfractions. 4. Two proteins are found in the region of apolipoprotein (apo) B-100 in VLDL and LDL and a third similar to apoB-48 is in VLDL. 5. Lecithin:cholesterol acyl transferase is active in plasma and hepatic lipase and lipoprotein lipase are evident in post-heparin plasma. 6. There is no si...
Delbeke FT, Vynckier L, Debackere M.A high performance liquid chromatographic method is described to determine the anti-inflammatory drug suxibuzone (SXB) and its major metabolites phenylbutazone (PBZ) and oxyphenbutazone (OPBZ) in equine plasma and urine. When suxibuzone (6 mg/kg) was administered intravenously (i.v.) or orally (p.o.) no parent drug was detected in plasma or in urine. The disposition of the metabolite PBZ (i.v.) could be described by a 2 compartment model with a beta half-life varying from 7.40 to 8.35 h. Due to severe side effects the use of i.v. suxibuzone should not be encouraged in the horse. PBZ and OPBZ w...
McKeever KH, Hinchcliff KW, Cooley JL, Lamb DR.The purpose of this study was to test the hypothesis that furosemide administration before exercise would cause greater increases in plasma arginine vasopressin (AVP) concentration in exercising horses than exercise alone. Six adult, clinically normal, unfit mares underwent three randomly ordered 60 minute standard exercise tests on an equine treadmill to examine the effect of furosemide administration on plasma AVP concentration. In one trial, furosemide (1 mg kg-1) was infused four hours before exercise (FUR-4) and a placebo (10 ml saline) was infused two minutes before exercise; in another ...
Art T, Lekeux P.This study was conducted in order to assess whether exercise- and training-induced cardio-respiratory adjustments are modified during the 10-day period which follows a booster vaccination with an oily adjuvanted inactivated vaccine against influenza and equine herpesvirus-1 (Equiffa). Nine healthy vaccinated thoroughbred horses were used. Six were revaccinated and three were kept as control. All the horses completed a standardised exercise test (SET) that was repeated 4 times, i.e. 10 (SET1) and 2 (SET2) days before revaccination, and 2 (SET3) and 10 (SET4) days after revaccination. During the...
Hinchcliff KW, McKeever KH, Muir WW, Sams R.The effect of furosemide-induced weight loss on the energetic responses of horses to running was examined in a 3-way crossover study. Eight 2- to 3-year-old Standardbred mares received, in random order, 10 ml of saline solution 4 hours before running on a treadmill (control trial, C); or, during 2 trials, 1 mg of furosemide/kg of body weight, i.v., 4 hours before running. During one of the trials when the horses received furosemide, they carried weight equal to that lost over the 3.75 hours after furosemide administration while running (furosemide-loaded, FL), and during the other trial they d...
Baker SJ, Gerring EL, Fox MT.Gastric pH varied widely among eight fasted ponies, of which seven exhibited discrete episodes of spontaneous alkalinisation (SA). SA occurred at all times of the study and no significant variation in the summary variables of pH (median pH, mean pH and percentage of readings exceeding pH 4.0) was noted among the periods 0 to eight, eight to 16 and 16 to 24 hours. The occurrence of SA has significant implications for the performance of acid secretory studies in the fasted pony. There was, however, no significant correlation between pH and plasma gastrin concentration measured using a commercial...
Komori M, Higami A, Imai Y, Imaoka S, Funae Y.A form of P450 [termed P450(h-1)] was purified from the liver microsomes of a male horse to electrophoretic homogeneity. The specific content of the final P450(h-1) preparation was 14.8 nmol/mg of protein and the recovery was 0.38% of the microsomal P450. The apparent molecular weight of P450(h-1) was 52,000 Da. The absorption spectra of P450(h-1) indicated that P450(h-1) was a low- and high-spin mixed type P450 in the oxidized form. The reconstituted system containing P450(h-1) could catalyze benzphetamine N-demethylation, 7-ethoxycoumarin O-deethylation, and testosterone 16 alpha-hydroxylati...
Bolann BJ, Ulvik RJ.The redox interaction between O2.- and ferritin cannot solely be regarded as as a Fe(II) release reaction. We demonstrate that native copper bound to horse spleen ferritin and apoferritin, stimulated the decay of O2.- in a catalytic reaction. Copper was determined by atomic absorption spectrophotometry. Decay of O2.- was monitored spectrophotometrically as the decrease in (A250-A360) at pH 9.5. The catalytic effect was linearly related to the copper content of the protein. Ferritin copper was less efficient than equimolar CuCl2, and iron-poor ferritin was more efficient than iron-rich ferritin...
Mihajlovic V, Cascone O, Biscoglio de Jiménez Bonino MJ.1. Reactivity of methionine residues towards Chloramine-T was studied in the equine growth hormone. 2. With a 20.0-fold molar excess of reagent over methionine, full oxidation of the four residues of the protein is achieved. 3. Methionine 4 is the most reactive group, followed by methionines 72 and 178--methionine 123 being the less reactive residue. 4. As judged by circular dichroism spectra and binding assays, protein conformation and binding capacity to specific receptors remains unchanged even after full oxidation of all four methionine residues. 5. Results agree with data previously obtai...
McDaniel AL, Martin SA, McCann JS, Parks AH.The objective of this study was to examine the effects of Aspergillus oryzae fermentation extract on the in vitro equine cecal fermentation of soluble starch, amino acids/peptides, coastal bermudagrass hay, and alfalfa hay. Cecal contents were obtained from a cecally fistulated Quarter Horse gelding fed coastal bermudagrass and grain (70:30) either unadapted or adapted to dietary A. oryzae supplementation (2 g/d). Mixed cecal microorganisms were incubated in anaerobic media for either 24 h (soluble starch, amino acids) or 48 h (bermudagrass hay, alfalfa hay). A. oryzae was added to the incubat...
Naylor JR, Bayly WM, Schott HC, Gollnick PD, Hodgson DR.The effects of dehydration and 40 min of exercise at approximately 40% of maximal O2 consumption on plasma volume (PV) and blood volume (BV) were studied in six horses. Horses were exercised while euhydrated (C); 4 h after administration of furosemide (1.0 mg/kg i.v.; FDH), which induced isotonic dehydration; and after 30 h without water (DDH), which caused hypertonic dehydration. Dehydration resulted in decreases of 6.3 and 9.9% for PV and BV, respectively, with FDH and 10.7 and 8.5%, respectively, with DDH. During exercise in C, PV and BV increased by 12.7 and 20.0%, respectively; during exe...
Naylor JR, Bayly WM, Gollnick PD, Brengelmann GL, Hodgson DR.Effects of dehydration on thermoregulatory and metabolic responses were studied in six horses during 40 min of exercise eliciting approximately 40% of maximal O2 consumption and for 30 min after exercise. Horses were exercised while euhydrated (C), 4 h after administration of furosemide (FDH; 1.0 mg/kg i.v.) to induce isotonic dehydration, and after 30 h without water (DDH) to induce hypertonic dehydration. Cardiac output was significantly lower in FDH (144.1 +/- 8.0 l/min) and in DDH (156.6 +/- 6.9 l/min) than in C (173.1 +/- 6.2 l/min) after 30 min of exercise. When DDH, FDH, and C values we...
Alexander SL, Irvine CH, Livesey JH, Donald RA.The effect of an acute fall in plasma cortisol on the secretion of CRH, arginine vasopressin (AVP), and ACTH was studied using our nonsurgical technique for collecting pituitary venous (PV) blood from horses. PV blood from six mares was collected continuously and divided into 30-sec segments for 0.5 h before and during a 3-h infusion of metyrapone, an 11-beta-hydroxylase inhibitor. During treatment, plasma cortisol fell (P < 0.01) to a mean nadir of 15% of pretreatment levels, and 11-deoxy-cortisol rose (P < 0.02). Three mares became mildly agitated during treatment. Mean PV concentratio...
Santucci R, Ascoli F, La Mar GN, Pandey RK, Smith KM.The reconstitution kinetics of horse heart myoglobin, as met-cyano derivative, with two synthetic hemins in which the 6- or the 7-propionate is replaced by a methyl group, has been investigated by circular dichroism, in order to gain information on the heme re-orientation process following the heme insertion into the globin pocket. The results obtained confirm that the preferred heme orientation places the sole propionate into the position occupied by the 6-propionate in the crystal structure, supporting the importance of the salt bridge occurring between this propionate and the basic CD3 resi...
Stewart F, Goode JA, Allen WR.A heterologous radioimmunoassay was developed and validated for the measurement of horse GH in plasma. It utilized recombinant-derived bovine GH as the radiolabelled ligand, a guinea-pig anti-porcine GH serum as first antibody and pituitary-derived horse GH as standard. Cross-reactivities were high with all of the pituitary and recombinant-derived GH preparations tested (49-140%) and very low (< 0.3%) with horse FSH, LH and prolactin. A synthetic analogue of GH-releasing factor(1-29) stimulated the expected pattern of GH release in foals. Plasma GH concentrations in foals were low at birth (< ...
Southwood LL, Evans DL, Hodgson DR, Bryden WL, Rose RJ.The effects of roughage source on metabolism and exercise capacity were investigated using 6, previously conditioned, mature thoroughbred horses in a cross-over experiment. The horses were assigned to either non-alfalfa or alfalfa roughage diets which were isocaloric. The diets were fed for 2 weeks, after which the horses were exercise tested and then fed the alternate diet. Horses were exercised on a high-speed treadmill using a rapid incremental test. Arterial blood samples were collected for blood gas analysis and acid base measurements and venous blood samples for lactate and red blood cel...
Beech J, Lindborg S, Braund KG.Potassium concentrations were measured in semimembranosus muscle, plasma and erythrocytes, and the urinary fractional excretion determined in normal horses and those that had chronic intermittent exercise-associated rhabdomyolysis. Muscle from the rhabdomyolysis horses was also evaluated microscopically. The horses with rhabdomyolysis had a lower muscle potassium concentration on a dry weight basis. Although the wet weight potassium content was also lower, the difference was not significant. Urinary fractional excretion of potassium (and also sodium and chloride) did not differ significantly b...
Fletcher JE, Erwin K, Beech J.Previous studies have demonstrated that phenytoin decreases the levels of triacylglycerols in several tissues other than skeletal muscle. Since phenytoin is clinically effective in several skeletal muscle disorders, triacylglycerol metabolism in skeletal muscle from four normal Quarter horses and four Quarter horses with hyperkalemic periodic paralysis was examined. The horses with hyperkalemic periodic paralysis had low levels of 18:3 in the phospholipids, low levels of 16:0, 16:1 and 18:3 in the free fatty acids and low levels of 20:4 in triacylglycerols. Triacylglycerol levels were increase...
Hope E, Johnston SD, Hegstad RL, Geor RJ, Murphy MJ.A commercially available radioimmunoassay kit for measurement of human osteocalcin was validated for use in horses. For accurate measurement of equine serum osteocalcin, blood samples may be collected at a temperature between 20 and 25 C, then centrifuged within 90 minutes; serum may be stored at -20 C in plastic tubes for up to 26 weeks. Serum may be thawed and refrozen up to 5 times without significant change in measured equine serum osteocalcin concentration. Assay sensitivity was 0.16 ng/ml. Recovery of bovine osteocalcin standard added to equine serum was linear. Intra-assay coefficient o...
Steffey EP, Dunlop CI, Cullen LK, Hodgson DS, Giri SN, Willits N, Woliner MJ, Jarvis KA, Smith CM, Elliott AR.Cardiovascular and respiratory changes that accompany markedly long periods (12 hours) of halothane anesthesia were characterized. Eight spontaneously breathing horses were studied while they were positioned in left lateral recumbency and anesthetized only with halothane in oxygen maintained at a constant end-tidal concentration of 1.06% (equivalent to 1.2 times the minimal alveolar concentration for horses). Results of circulatory and respiratory measurements during the first 5 hours of constant conditions were similar to those previously reported from this laboratory (ie, a time-related sign...
Butler PJ, Woakes AJ, Smale K, Roberts CA, Hillidge CJ, Snow DH, Marlin DJ.A new design of flowmeter is described and used in a comprehensive study of the respiratory and cardiovascular adjustments that occur during a standardised exercise test in Thoroughbred horses. The flowmeter system and associated lightweight, fibreglass mask (total mass, 0.7 kg) have a maximum dead space of 500 ml and negligible resistance to airflow. They have no systematic effect on blood gases and, together with a rapidly responding mass spectrometer, enable an accurate computation of gas exchange to be performed together with breath-by-breath determination of other respiratory variables. A...
Freeman DE.Accumulation of D-xylose by jejunal mucosa from healthy horses and rabbits was studied in vitro. When tissue sheets were incubated with 1 mM D-xylose for 60 minutes, mucosa from horses and rabbits accumulated D-xylose against a concentration gradient. There was no accumulation when equine specimens were incubated with 5 mM D-xylose. By comparison, equine jejunum accumulated D-glucose against a concentration gradient when incubated in 5 mM D-glucose. In equine and rabbit jejunum, 13.3 +/- 7.0% and 36 +/- 11.0%, respectively, of accumulated D-xylose was phosphorylated when sheets were incubated ...
Kohn CW, Sams R, Kowalski JJ, Powers J, Wallace S.The disposition of rifampin in six healthy mares after single intravenous (i.v.) and oral (p.o.) doses and after seven oral doses of 10 mg/kg administered twice a day was investigated using a high performance liquid chromatographic (HPLC) method. Pharmacokinetic variables for rifampin determined using the HPLC method were comparable to variables reported from earlier studies utilizing a microbiological assay. Desascetylrifampin, a major metabolite of the parent compound, could not be detected in the serum but was detected at low concentrations in urine. Mean trough concentrations of rifampin i...
Moslemi S, Dintinger T, Dehennin L, Silberzahn P, Gaillard JL.The ability of human and equine placental microsomes to aromatize 7 alpha-methyl-19-nortestosterone (MNT) was studied. Kinetic analysis indicates that MNT shares the androgen-binding site of human and equine placental microsomal aromatases. Human placental microsomal estrogen synthetase had about a 2.5-fold higher relative affinity for MNT than the equine placental enzyme (KiMNT/Km androstenedione of 32 versus 87). However, MNT was not metabolized by human placental microsomes, whereas it was very actively metabolized by equine placental microsomes. Further studies using purified equine cytoch...
Geelen SN, Blázquez C, Geelen MJ, Sloet van Oldruitenborgh-Oosterbaan MM, Beynen AC.The metabolic effects of feeding soyabean oil instead of an isoenergetic amount of maize starch plus glucose were studied in ponies. Twelve adult Shetland ponies were given a control diet (15 g fat/kg DM) or a high-fat diet (118 g fat/kg DM) according to a parallel design. The diets were fed for 45 d. Plasma triacylglycerol (TAG) concentrations decreased by 55 % following fat supplementation. Fat feeding also reduced glycogen concentrations significantly by up to 65 % in masseter, gluteus and semitendinosus muscles (P < 0.05 and P < 0.01 and P < 0.01 respectively). The high-fat diet significan...
Evans MJ, Mulligan RS, Livesey JH, Donald RA.Perifused equine anterior pituitary cells were used to investigate the relationships between the secretion of ACTH and substances known to either stimulate (corticotrophin-releasing hormone (CRH), and arginine vasopressin (AVP)) or inhibit (cortisol) ACTH secretion. The experiments were designed to mimic the hormone milieu present in vivo in the horse, with cortisol (0 or 100 nmol/l) and CRH (0 or 0.02 nmol/l) perifused continuously, and pulses of AVP (10 nmol/l) applied for 5 min at 30-min intervals. In columns perifused with 0.02 nmol CRH/l there was no significant overall effect of 100 nmol...
Uboh CE, Rudy JA, Soma LR, Fennell M, May L, Sams R, Railing FA, Shellenberger J, Kahler M.The purpose of this study was two-fold: (1) to develop a simple and sensitive screening procedure for identifying and confirming bromhexine and ambroxol and, (2) to determine the effect of furosemide on the detection of bromhexine, ambroxol, or their metabolites in urine. Female horses (450-550 kg) treated with bromhexine or ambroxol (1 g, p.o.) were used. Urine samples were collected up to 48 h post-drug administration and analysed. Blind samples were used in evaluating the sensitivity of these methods and reproducibility of the results. Bromhexine and ambroxol were extensively metabolized in...
Vervuert I, Coenen M, Wedemeyer U, Chrobok C, Harmeyer J, Sporleder HP.Physical exercise is known to affect calcium homeostasis in horses, but there is little information on the hormonal regulation of calcium metabolism during exercise. In order to evaluate the effects of exercise and training on calcium homeostasis and intact plasma parathyroid hormone, 7 untrained Standardbred horses were studied in a 6 week training programme. These horses were accustomed to running on the treadmill 3 weeks before onset of training and were exercised on a high-speed treadmill with an initial incremental standardised exercise test (SET 1: 6 incremental steps of 5 min duration e...
Meier AD, de Laat MA, Reiche DB, Sillence MN.Endocrinopathic laminitis, related to equine metabolic syndrome and insulin dysregulation, causes marked pain and suffering in horses and represents a substantial cost to the horse industry. This study investigated the effect of feeding a diet high in nonstructural carbohydrates on concentrations of active glucagon-like peptide-1 (aGLP-1), total insulin-like growth factor-1 (IGF-1), and high-molecular-weight (HMW) adiponectin, in insulin-dysregulated ponies. Thirty-seven ponies were challenged with this diet for up to 18 d to induce hyperinsulinemia. Hormone concentrations were measured in se...
Shults T, Kownacki AA, Woods WE, Valentine R, Dougherty J, Tobin T.In horses given (rapid IV) methylphenidate (Ritalin, alpha-phenyl-2-piperidinacetic acid methyl ester; 0.70 mg/kg), plasma concentrations of the drug decreased rapidly at first, with an apparent alpha half-life of about 19 minutes, and then more slowly, with an apparent beta half-life of about 2.4 hours. These data were well fitted by a 2-compartment open model. In blood, about 40% of the methylphenidate present was in the plasma fraction, and of this, about 80% was plasma-protein bound. If given by subcutaneous or IM injection, plasma concentrations of methylphenidate peaked in about 1 hour a...
MacDonald MH, Stover SM, Willits NH, Benton HP.The metabolic responses of equine articular cartilage to incubation with bacterial lipopolysaccharide (LPS) were studied, using explant cultures of articular cartilage obtained from the metatarsophalangeal joints of 15 horses, age of which ranged from 3 months to 20 years. For comparison, explants were also established from the metatarsophalangeal joints of 3 calves. Explants were cultured for 3 days in medium containing various concentrations of LPS from 0 (control) to 100 micrograms/ml. Glycosaminoglycan (GAG) released during the 3-day incubation was determined by a spectrophotometric assay,...
Stokes SM, Bertin FR, Stefanovski D, Poulsen L, Belknap JK, Medina-Torres CE, Pollitt CC, van Eps AW.Continuous digital hypothermia (CDH) prevents lamellar failure in the euglycaemic hyperinsulinaemic clamp (EHC) and oligofructose (OF) laminitis models, but the mechanisms remain unclear. Objective: To evaluate the effects of CDH on lamellar energy metabolism and perfusion in healthy horses and during EHC and OF laminitis models. Methods: In vivo experiment. Methods: Archived samples were used from Standardbred geldings that received no treatment (CON) (n = 8) or underwent EHC (n = 8) or OF (n = 6) laminitis models. Both forelimbs were instrumented with a lamellar microdialysis system, a...
Peters GJ, Oosterhof A, Veerkamp JH.1. Adenosine inhibits thymidine and uridine incorporation of PHA-stimulated lymphocytes of man and horse at concentrations higher than 50 and 10 microM, respectively. Deoxyadenosine is inhibitory at concentrations higher than 100 microM. Thymidine and uridine incorporation of porcine lymphocytes are elevated 5-7-fold by 25-100 microM adenosine, deoxyadenosine, inosine and hypoxanthine. Leucine incorporation of PHA-stimulated lymphocytes was affected by adenosine and deoxyadenosine in the same way, but to a lower extent. 2. Effects of adenosine and deoxyadenosine were more pronounced at shorter...
Ellis EJ, Ravis WR, Malloy M, Duran SH, Smyth BG.Six horses were administered either 15 or 20 mg/kg body weight (b.w.) procainamide (PA) as an intravenous (i.v.) dose over 10 min. The plasma concentrations of PA and N-acetylprocainamide (NAPA) as well as the pharmacodynamic effect (prolongation of the QT interval) were monitored. The PA plasma concentrations could be described by a one-compartment model with a t1/2 of 3.49 +/- 0.61 h. The total body clearance of PA was 0.395 +/- 0.090 l/hr/kg and the volume of distribution was 1.93 +/- 0.27 l/kg. As observed after PA administration, NAPA (an active metabolite) had a t1/2 longer than PA of 6....
Sarasola P, McKellar QA.A regime for administration of ampicillin sodium by continuous intravenous infusions to horses was designed. The aim was to achieve plasma ampicillin concentrations between 5 and 10 micrograms/ml over a 4-h period. A 2 mg/kg bodyweight loading dose of ampicillin sodium was administered intravenously at the beginning of the infusion in order to achieve steady-state plasma concentrations rapidly. The infusion system subsequently administered ampicillin at a rate of approximately 19.2 micrograms/min/kg bodyweight. The plasma concentrations obtained over the infusion period correlated very well wi...
Sutton GJ, Cawley A, Murphy C, Lau ML, Hibbert DB.Horse racing authorities impose a limit on the concentration of plasma 'total carbon dioxide' (TCO2), typically 36 mM with action taken above 37 mM, as measured by an electrochemical gas analyzer. It is of interest to understand the distribution of TCO2 in a 'normal' population of racehorses and determine probabilities of members of this population exceeding these current regulatory and action limits. TCO2 levels in equine plasma samples have been modelled for 12 months (2011-2012) of thoroughbred (3076 measurements) and standardbred (3788 measurements) data in Australia. The two populations h...
Davis MS, Barrett MR.Mitochondrial function-oxidative phosphorylation and the generation of reactive oxygen species-is critical in both health and disease. Thus, measuring mitochondrial function is fundamental in biomedical research. Skeletal muscle is a robust source of mitochondria, particularly in animals with a very high aerobic capacity, such as horses, making them ideal subjects for studying mitochondrial physiology. This article demonstrates the use of high-resolution respirometry with concurrent fluorometry, with freshly harvested skeletal muscle mitochondria, to quantify the capacity to oxidize substrates...
Stanley SM, Kent S, Rodgers JP.In this study the equine metabolism of fluoxymesterone (9alpha-fluoro-11beta-17beta-dihydroxy-17alpha-meth ylandrost-4-ene-3-one) given orally has been investigated. The parent material was not detected, but two major 16-hydroxy metabolites which corresponded to a mono- and a di-hydroxylation product were evident. One of the hydroxylation positions was identified as C-16. Phase II metabolism in the form of glucuronide formation was also common. These steroids will provide target compounds for confirming abuse of this drug in the horse.
Davie AJ, Evans DL, Hodgson DR, Rose RJ.The aim of this study was to investigate the effects of reduced muscle glycogen concentration on some physiological and metabolic responses during moderate intensity treadmill exercise in horses. Six Thoroughbred geldings were randomly allocated to 2 treatments (protocols A and B) or control in a 3 x 3 replicated Latin square design. In protocol A, horses performed low intensity exercise while horses in protocol B performed short bursts of high intensity exercise. Protocol A was designed to induce glycogen depletion mainly of slow twitch muscle fibers while protocol B aimed to deplete mainly f...
Brobst DF, Carroll RJ, Bayly WM.Urinary concentrations of gamma glutamyl transferase (GGT), alkaline phosphatase (AP), aspartate aminotransferase (AsAT), and alanine aminotransferase (AAT) were measured in 32 healthy horses (16 geldings and 16 females) at the same time on 2 consecutive days. The subjects were divided into 4 ages groups, each comprising 8 horses (4 of each sex). In 10 of the geldings, urine was collected continuously for 72 hours, with catheterized samples being obtained at 0800, 1400 and 2000 hours, and an aliquot of the pooled urine being taken every 24 hours. Urinary enzyme activity was found to be unrelat...
Mills PC, Ng JC, Auer DE.The effect of the acute-phase response (APR) on the activity of the hepatic drug-metabolizing system (DMS) and on the binding of phenylbutazone to plasma proteins was investigated in the horse. An APR was induced by intramuscular injections of Freund's complete adjuvant in five horses and, five days later, these horses together with five clinically normal horses were shot and the right ventral lobe of each liver removed. The hepatic microsomal fractions from the liver samples were isolated and significantly lower (p < 0.01) concentrations of cytochromes P450 and b5 and activities of aniline...
Rose RJ, Schlierf HA, Knight PK, Plummer C, Davis M, Ray SP.In a crossover study, either a placebo paste or N,N-dimethylglycine was administered orally at a dose rate of 1.2 mg/kg twice daily for five days to six thoroughbred horses, with bodyweights ranging from 424 to 492 kg. Using previously determined regression equations for oxygen uptake (VO2) against speed for each horse, a standardised exercise test was given with speeds equivalent to fixed percentages of the maximum oxygen uptake (VO2max). The test consisted of two minutes at speeds equivalent to approximately 40 per cent and 50 per cent VO2max, and one minute at speeds that produced approxima...
Cárceles-Rodríguez CM, Fernández-Varón E, Martín-Gimenez T, Aguirre C, Arion A, Rodríguez MJ, Ayala I.Insulin dysregulation (ID) is a common metabolic disorder in horses. Recently, incretin hormone release has been suggested to be involved in ID in horses. In human medicine, metformin and sitagliptin are commonly used in combination for metabolic syndrome. This combination could be useful in treating ID in horses. However, no pharmacokinetics data have been reported in this species. The objective of the present study was to establish the plasma concentration-time profile and to derive pharmacokinetics data for a combination of metformin and sitagliptin in horses after enteral administration. S...
Becker F, Kurth J, Schneider F, Nürnberg G, Heinrich H, Kanitz W.The aim of this study was to prove if oxidation-reduction levels in the follicular fluid were new functional indices of follicular health and whether there was a high level of accordance with endocrinological parameters and with the growth stage as detected by ultrasound monitoring of individual follicles during the oestrous cycle in mares. Follicles were classified as growing and regressing follicles using ultrasonography. Altogether 48 follicles with a diameter from 20 to 56 mm were aspirated by transvaginal ultrasound guided follicular aspiration. Follicular concentration of oestradiol and ...
Rooney MF, Neto NGB, Monaghan MG, Hill EW, Porter RK.Thoroughbred racehorse performance is largely influenced by a major quantitative trait locus at the () gene which determines aptitude for certain race distances due to a promoter region insertion mutation influencing functional phenotypes in skeletal muscle. To develop an system for functional experiments we established three novel equine skeletal muscle cell lines reflecting the variation in phenotype associated with genotype (CC/II, CT/IN and TT/NN for SNP g.66493737C > T/SINE insertion 227 bp polymorphism). Primary equine skeletal muscle myoblasts, isolated from Thoroughbred horse , we...
Nouws JF, Vree TB, Baakman M, Driessens F, Smulders A, Holtkamp J.The plasma disposition of sulfadimidine (SDM) and its metabolites N4-acetylsulfadimidine (N4-SDM), 6-hydroxymethyl-4-methyl-pyrimidine (SCH2OH) and 5-hydroxy-4,6-dimethyl-pyrimidine (SOH), was studied in three horses following intravenous administration of SDM at dose levels of 20 and 200 mg/kg in cross-over trials. The percentages of N4-SDM (0.58-0.90%), SOH (0.83-6.75%) and SCH2OH (0.38-0.71%) in plasma, expressed as a percentage of the total sulfonamide concentration, were small and their plasma concentrations were parallel with SDM from 4 h following administration. At high doses (200 mg/k...
Harris RC, Harris PA, Routledge NB, Naylor JR, Wilson AM.Pharmacological benefits of glutamine supplementation have been shown in athletically and clinically stressed human subjects. In the horse, infection and intense exercise have also been shown to significantly decrease plasma glutamine concentrations, but little is known on how best to supplement. Objective: To evaluate whether ingestion of different foodstuffs, with or without L-glutamine (G) or a peptide (Pep) containing 31.5% w/w G in a water-stable form, could affect plasma glutamine concentrations (P-GC). Methods: Nine feeds (molassed sugar beet-pulp (mSB); naked oats (nO); commercial mix ...
Fitzgerald BP, Reedy SE, Sessions DR, Powell DM, McManus CJ.The seasonal nature of reproductive activity in mares is widely accepted and considerable attention has focused on the mechanisms that lead to the initiation of the breeding season. In contrast, considerably less information is available about the termination of the breeding season. It is interesting to note that each winter a sub-population of mares continues to undergo oestrous cyclicity during the non-breeding season. Continuation of reproductive activity during the winter occurs most frequently in mares that maintain a non-pregnant condition in successive years. The maintenance of a non-pr...
Jellyman JK, Valenzuela OA, Allen VL, Holdstock NB, Fowden AL.Pancreatic β cells are responsive to a range of stimuli during early post natal life in healthy pony foals. However, little is known about whether these responses are sex-linked. Objective: To determine pancreatic β cell responses to the insulin secretagogues, glucose, arginine and tolbutamide, in fillies and colts during the first 3 months after birth. Methods: In vivo experiment examining sex differences in pancreatic β cell function in foals. Methods: Female (n = 8) and male (n = 5) pony foals were infused i.v. with glucose (0.5 g/kg bwt 40% dextrose), arginine (100 mg/kg bwt) or tol...
Senra RL, Ramírez-López CJ, Magalhães-Júnior MJ, Neves JGDS, Barros E, Waddington B, Guimarães SEF, Guimarães JD, Baracat-Pereira MC.Horses are seasonal polyoestrous animals, and the photoperiod is the main factor modulating their reproductive activity. There is no consensus on the andrological and biochemical factors that influence breeding seasonality. To assess the involvement of climate in reproduction, Mangalarga Marchador stallions were monitored over 1 year regarding semen quality and seminal plasma proteome. Here, we show that kallikrein (KLKs) proteoforms in seminal plasma are involved in climate conditioning of reproduction. During the breeding season, greater abundance and different types of KLKs occurred simult...
Takahashi Y, Takahashi T.Domesticated horses adapt to environmental conditions through seasonal fluctuations in their metabolic rate. The seasonal change of metabolic rates of domesticated horses in pastures is documented. However, there are few investigations on seasonal body weight change of domesticated horses housed in stables, which are provided constant energy intake throughout the year. Both seasonal changes and gain in body weight of racehorses during their athletic career is known to a lesser extent because their body weight are not measured in most countries. Here, we used a seasonal-trend decomposition meth...
Gronwall R, Engelking LR.The effects of several treatments and their routes of administration on the reduction of hyperbilirubinemia in 9 pony mares after a 3-day fast were studied. Treatments were as follows: glucose given at doses of 1.2, 2.4, and 3.7 mg/min/kg of body weight; refeeding the base-line diet; feeding straw; and IV administration of taurocholic acid at a dosage of 0.07 mumol/min/kg. The 3 glucose dosages were each given by 3 different routes: IV, intraduodenal, and intragastric. The smallest dosage of glucose given by IV route reduced the plasma bilirubin concentration only 7%, even though other measure...
Schmitz A, Portier CJ, Thormann W, Theurillat R, Mevissen M.Stereoselectivity has to be considered for pharmacodynamic and pharmacokinetic features of ketamine. Stereoselective biotransformation of ketamine was investigated in equine microsomes in vitro. Concentration curves were constructed over time, and enzyme activity was determined for different substrate concentrations using equine liver and lung microsomes. The concentrations of R/S-ketamine and R/S-norketamine were determined by enantioselective capillary electrophoresis. A two-phase model based on Hill kinetics was used to analyze the biotransformation of R/S-ketamine into R/S-norketamine and,...
Viafara JAS, Portilho RV, Maculan R, Souza Júnior JF, Silva CM, Rodrigues PG, El Azzi MS, Souza JC.This study evaluated the presence of polyunsaturated fatty acids in circulating blood and in the ovarian follicular fluid of mares, after supplementation of the diet with linseed oil. Six Mangalarga Marchador mares, weighing 397.00±31.89 kg, were kept on native pasture, and assigned to the current study. In a switch over design, mares were randomly allocated to receive 150 ml of vegetable oil daily, containing polyunsaturated fatty acids n3 (62.23 g ALA, 20.34 g LA, 2.27 g EPA, 2.32 g DHA), (n=3) or no supplementation (n=3) in two replicates. Blood and follicular fluid samples were taken on t...
