The physiology of horses encompasses the study of the biological functions and processes that occur within the equine body. This includes the examination of various systems such as the cardiovascular, respiratory, musculoskeletal, digestive, and nervous systems. Understanding equine physiology is essential for comprehending how horses adapt to different environmental conditions, perform physical activities, and respond to health challenges. Research in this field often focuses on the mechanisms of energy metabolism, thermoregulation, and muscle function during exercise, as well as the physiological responses to stress and disease. This page compiles peer-reviewed research studies and scholarly articles that explore the diverse aspects of equine physiology, providing insights into the biological processes that support the health and performance of horses.
Van den Oord AH, Wesdorp JJ, Van Dam AF, Verheij JA.In commercial samples of equine myoglobin and samples of equine and bovine myoglobin prepared in the laboratory, a small amount of the protein was present as an aggregate. The presence of the myoglobin aggregate could be demonstrated by gel filtration on Sephadex G-100 Superfine, which also provided a means of isolating it. Gel filtration on Sephadex G-100 showed the molecular weights of the equine and bovine moyglobin aggregates to be about 35000 and 34000 respectively, thus supporting the hypothesis that they are dimers. This was confirmed for the equine myoglobin by ultracentrifugation meas...
Darke PG, Holmes JR.The paper describes the distribution of cardiac potentials on the body surface of four horses. Potentials were recorded at 200 to 300 equallyspaced sites synchronously with a reference lead; they were measured at 10 msec. instants of time, and were plotted on diagrams. While some evidence of multiple dipolar activity occurred during each part of the cardiac cycle, the majority of potentials arose as if from a single resultant dipole.
Slade LM, Hintz HF.A comparative digestion trial was conducted between horses, ponies, rabbits and guinea pigs. Alfalfa and alfalfa-grain diets were compared.
Although there was a trend for ponies to be more efficient than horses in digesting proximate principles of both diets, differences were not significant. Digestibility coefficients for crude fiber and energy were lowest in rabbits. The digestion of nitrogen-free extract (NFE) was greatest in guinea pigs, whereas digestion of crude protein was lowest.
Horses, ponies and rabbits digested organic matter, NFE and energy in the mixed ration more efficient...
Lees P, Tavernor WD.1. In horses anaesthetized with halothane the intravenous administration of suxamethonium chloride, at a dose level of 0.2 mg/kg, produced a short-lived period of hypoventilation, which was associated with increases in arterial blood PCO(2) levels and in plasma concentrations of bicarbonate, sodium and potassium ions, and reductions in arterial blood pH and PO(2) values.2. The respiratory depressant action of suxamethonium chloride 0.2 mg/kg was accompanied by increases in blood pressure and heart rate. Doses of suxamethonium chloride 0.4 mg/kg produced similar but quantitatively greater chang...
Mori M, Sakiyama Y.The histochemical distribution of some hydrolytic and oxidative enzymes in developing odontoblasts and subodontoblasts in cattle, pigs and horses has been observed in cryostat sections of teeth that have been decalcified with neutral EDTA.
Undifferentiated dental epithelium and immature odontoblasts of the bell stage tooth germ showed lower levels of enzymatic activity as compared with the well-developed tooth germ.
When the dentine matrix began to form, the young odontoblasts appeared to have a significantly positive reaction for acid phosphatase, and gradually other enzymes developed a...
Simon SR, Cantor CR.The UV circular-dichroism spectra of human and horse hemoglobins have been determined at various degrees of partial saturation with oxygen. Spectra of the two native hemoglobins were compared with spectra of the corresponding proteins modified with a reagent known to eliminate the conformational rearrangement normally associated with cooperativity. Such comparison indicates that one region, around 260 mmu, is sensitive chiefly to the state of the hemes; changes in another region, around 285 mmu, may be correlated with the conformational transformation linked to cooperative interactions. All ci...
Cenani A, Brosnan RJ, Madigan S, Knych HK, Madigan JE.Propranolol has been suggested for anxiolysis in horses, but its sedation efficacy and side effects, both when administered alone and in combination with α-adrenoceptor agonists, remain undetermined. This study aimed to document the pharmacokinetics and pharmacodynamics of propranolol, romifidine and their combination. Methods: Randomized, crossover study. Methods: Six adult horses weighing 561 ± 48 kg. Methods: Propranolol (1 mg kg; treatment P), romifidine (0.1 mg kg; treatment R) or their combination (treatment PR) were administered intravenously with a minimum of 1 week between treatment...
Doreau M, Dussap G.Female milk production was related to offspring water turnover, estimated by a tracer method (fig. 1). After deuterium oxide was injected into the blood of the offspring, we measured the decrease of its concentration in time. Milk intake was calculated by equations taking into account the weight gain of the offspring. The reliability of this method was checked in 28 bottle-fed lambs with known milk intake; the correlation between the actual intakes and our estimates was 0.98 with an error means of 5.6 p. 100. The error on the mean of 28 lambs was 0.5 p. 100 (table 1). The milk production of 6 ...
Grubb TL, Constable PD, Benson GJ, Foreman JH, Olson WO, Thurmon JC, Tranquilli WJ, Davis LE.To determine the most repeatable method for evaluating right ventricular relaxation rate in horses and to determine and compare effects of isoflurane or halothane with and without the added influence of intravenously administered calcium gluconate on right ventricular relaxation rates in horses. Methods: 6 Thoroughbred horses from 2 to 4 years old. Methods: 6 models (2 for monoexponential decay with zero asymptote, 3 for monoexponential decay with variable asymptote, and 1 for biexponential decay) for determining right ventricular relaxation rate were assessed in conscious and anesthetized hor...
Wilson AM, Pardoe CH.Studies on horseshoe materials have been limited to the analysis of kinematic data to determine slip times and distances, since equine force plate analysis is traditionally undertaken on a rubber-surfaced force plate. The purpose of this study was to modify a force plate for measuring ground reaction forces on a road surface and report preliminary data from the system. A steel-reinforced concrete top plate of 18 mm thickness and mass 23 kg, and a 12 mm thick top plate of 6 mm bituminous macadam wear coat (road surface) contained in a tray constructed of 2 mm thick steel, mass 21 kg, were const...
Manohar M, Goetz TE, Nganwa D.Diaphragmatic O2 and lactate extraction were examined in seven healthy ponies during maximal exercise (ME) carried out without, as well as with, inspiratory resistive breathing. Arterial and diaphragmatic venous blood were sampled simultaneously at rest and at 30-s intervals during the 4 min of ME. Experiments were carried out before and after left laryngeal hemiplegia (LH) was produced. During ME, normal ponies exhibited hypocapnia, hemoconcentration, and a decrease in arterial PO2 (PaO2) with insignificant change in O2 saturation. In LH ponies, PaO2 and O2 saturation decreased well below tha...
Bartels JE, Beckett SD, Brown BG.Serial arteriography was used to determine the vascular pattern and blood flow in the penis of the pony stallion. Ponies were anesthetized with pentobarbital sodium, and catheters were surgically introduced into the internal pudendal and obturator arteries. The vascular anatomy was visualized by angiography via image-intensified fluoroscopy and was recorded on 70-mm film at 3 frames/s or by direct radiography. Blood flow into the corpus cavernosum penis (CCP) was limited during quiescence because the blood was immediately shunted into the venous system. After vasodilation with mild stimulation...
Jansen WL, van Alphen M, Berghout M, Everts H, Beynen AC.The ratio of calculated net energy intake (NEi) to calculate net energy requirement (NEr) might serve as an indicator of the efficiency of dietary energy utilization. The ratio was determined for 93 horses and ponies from 10 riding schools. For each animal with an assumed constant body weight, energy intake and energy requirements were assessed. On average, the estimated NEi was 14% greater than NEr. There was a significant, negative association between crude fibre intake and the NEi: NEr ratio. Earlier work indicated that extra fat intake may lead to over estimation of the calculated energy v...
Pedersoli WM, Ravis WR, Belmonte AA, McCullers RM.Digoxin (elixir, 0.022 mg/kg) was administered via stomach tube to healthy horses of mixed breeding and sexes. Serum digoxin concentrations reached a peak (2.21 +/- 0.6 ng/ml) at approximately 1 hour after dosing and had a half-life of 28.8 +/- 10.7 hours. Digoxin kinetics followed a triexponential curve, indicating that at least a 2 compartmental model is required to characterize the serum concentration-time curve after this route of administration. It was calculated that to achieve average serum concentrations of 1.1 ng/ml, an oral dose of 17.4 microgram of digoxin elixir/kg/day and an IV do...
Mizobe M, Kondo F, Toyoshima C, Kumamoto K, Terada T, Nasu H.A rapid method was developed to analyze delta-bilirubin (B delta), diconjugated bilirubin (DCB), monoconjugated bilirubin (MCB), and unconjugated bilirubin (Bu) by direct injection of sera using high-performance liquid chromatography (HPLC) with an internal-surface reversed-phase silica support (ISRP) column. Sharp bilirubin peaks were obtained using a simple mobile phase of acetonitrile: 0.5 M Tris-HCl buffer (20:80, v/v, pH 7.2). A variable-wavelength detector set at 450 nm, 0.01 absorbance unit full scale (AUFS), and a recorder set at 4 mm/min were used for detection. Peaks for B delta, DCB...
Soraci AL, Mestorino ON, Errecalde JO.The pharmacokinetics and bioavailability of cefoperazone (CPZ) were studied following intravenous (IV) and intramuscular (IM) administration of single doses (30 mg/kg) to horses. Concentrations in serum, urine and synovial fluid samples were measured following IV administration. CPZ concentrations in serum, synovial fluid and spongy bone samples were measured following IM administration. After IV administration a rapid distribution phase (t1/2 (alpha): 4.22 +/- 2.73 min) was followed by a slower elimination phase (t1/2(beta) 0.77 +/- 0.19 h). The apparent volume of distribution was 0.68 +/- 0....
Costa F, Brunsting J, Corrêa F.This case report describes a 16-year-old jumping stallion that had a marked swelling over the left antebrachial area along with substantial lameness after a fall. The horse was weight bearing but lame (4/5; AAEP scale) at the walk with marked enlargement in the caudal aspect of the antebrachial region. After a static musculoskeletal examination, radiography and ultrasonography the horse was diagnosed with flexor muscle myopathy and presumptive extremity compartment syndrome. Following medical treatment, the horse improved clinically over several days. Six-months post injury the horse showed fl...
Okumura M, Fujinaga T.The role of keratan sulphate (KS) as a metabolic marker of cartilage was evaluated using an in vitro model of equine articular cartilage. Articular cartilage was harvested from clinically healthy 6-month-old foals (n = 3). Chondrocytes were centrifuged and cultured as pellets. Chondrocyte pellets were stimulated by insulin-like growth factor-I alpha (IGF-I alpha) or interleukin-1 alpha (IL-1 alpha) for 2 weeks. The concentrations of sulphated glycosaminoglycans (GAG) and KS in the culture media were measured by a 1,9-dimethyl-methylene blue (DMMB) colorimetric assay and an inhibition enzyme-li...
Lizarraga I, Panizzi L, Gieseg MA, Riley CB, Chambers JP.To evaluate thermal nociceptive thresholds (TNTs) before and after inducing a standardized radiocarpal bone osteochondral fracture (OCF) in horses. Methods: Prospective, controlled, randomized, masked study. Methods: A group of 10 Thoroughbred fillies aged 2 years. Methods: Skin temperature and TNTs were measured on the skin over the triceps brachii muscle in both the thoracic limbs before (week 0) and weekly (weeks 1-8) after unilateral arthroscopic induction of a radiocarpal OCF (n = 4) or sham surgery (n = 6) followed by a standardized exercise programme. The contralateral, non-operated t...
Seamans KW, Sharp DC.Follicular aromatase activity during sexual resurgence after the winter anoestrus was investigated in 3 groups of 5 Pony mares. Group ET was studied during the early transition period, Group LT in late transition and Group C in full breeding condition. Granulosa and theca cells were incubated for 3 h with 3H-labelled androstenedione or progesterone. Analysis of the free oestrogenic products was by high performance liquid chromatography (HPLC) and recrystallization revealed highly variable oestrogen production in both cell types from mares in all 3 groups. Only oestrone and oestradiol peaks wer...
Ekici S, Ozmen O.The active roles of microribonucleic acids (miRNAs) in gene regulation have made miRNAs a key point for the scientific world in the study of physiological processes. Although saliva includes the largest number of miRNAs, there is no miRNA study in saliva on horses has been found. Our study is the first study on miRNAs isolation from saliva in horses. In the present study, saliva was studied in Arabian racehorses to better understand the molecular mechanisms of expression levels that are effective in lipid metabolism of miRNAs and their target genes during the race. Identification of lipid meta...
Aberle ED, Judge MD, Kirkham WW, Page EH, Crawford BH.Frozen sections of equine musculus semitendinosus were examined for myosin adenosine triphosphatase (ATPase) and reduced nicotinamide adenine dinucleotide-tetrazolium reductase (NADH-TR), using standard histochemical procedures, and the proportions of the various fiber types and average fiber sectional size were determined. With ATPase staining, approximately 70% of the fibers were classified as alpha fibers (ATPase positive), and 30%, as beta fibers (ATPase negative). In addition, 2 populations of alpha fibers could be readily distinguished on the basis of the intensity of the ATPase reaction...
Ingvast-Larsson C, Kallings P, Persson S, Appelgren LE, Wiese B.The pharmacokinetics of theophylline at rest and the effects on cardio-respiratory and blood lactate responses to exercise were investigated after repeated oral administrations in six healthy Standardbred horses. A dose of 5 mg/kg body weight was administered every 12 h. The binding of theophylline to plasma protein was also determined. There was good agreement between predicted and observed plasma concentrations of theophylline at steady state. The mean half-life of elimination was shown to be 17.0 +/- 2.5 h, the mean half life of absorption was 1.6 +/- 1.8 h, the apparent volume of distribut...
Steward KF, Harrison T, Robinson C, Slater J, Maskell DJ, Harris SR, Holden MTG, Waller AS.Opportunistic pathogens must adapt to and survive in a wide range of complex ecosystems. Streptococcus zooepidemicus is an opportunistic pathogen of horses and many other animals, including humans. The assembly of different surface architecture phenotypes from one genotype is likely to be crucial to the successful exploitation of such an opportunistic lifestyle. Construction of a series of mutants revealed that a serine recombinase, PinR, inverts 114 bp of the promoter of SZO_08560, which is bordered by GTAGACTTTA and TAAAGTCTAC inverted repeats. Inversion acts as a switch, controlling the tra...
Torres-Boggino F, Sato K, Oka A, Kanno Y, Hochi S, Oguri N, Braun J.Seminal characteristics, fertility and the response to semen preservation (liquid storage and cryopreservation) were evaluated in 4 Draft stallions (Percheron 2, Breton 2). Seminal characteristics (gel-free volume, sperm concentration, sperm morphology, percentage of motile spermatozoa) were assessed in 5 ejaculates from each of the 4 stallions. The fertility of the stallions was calculated retrospectively as the accumulated pregnancy rate over 3 breeding seasons. Five ejaculates from each of the stallions were subjected to liquid storage at 5 degrees C. The percentage of motile spermatozoa (P...
Kingston JK, Bayly WM, Sellon DC, Meyers KM, Wardrop KJ.To investigate the potential use of fluorescent-labeled annexin V, anti-human fibrinogen antibody, and anti-human thrombospondin antibody for detection of the activation of equine platelets by use of flow cytometry. Methods: Platelets obtained from 6 Thoroughbreds. Methods: Flow cytometry was used to assess platelet activation as indicated by detection of binding of fluorescent-labeled annexin V, anti-human fibrinogen antibody, and anti-thrombospondin antibody to unactivated and ADP-, collagen-, platelet activating factor (PAF)-, and A23187-activated equine platelets. Human platelets were used...
Bennett RC, Steffey EP, Kollias-Baker C, Sams R.To quantitate the dose and time-related effects of morphine sulfate on the anesthetic sparing effect of xylazine hydrochloride in halothane-anesthetized horses and determine the associated plasma xylazine and morphine concentration-time profiles. Methods: 6 healthy adult horses. Methods: Horses were anesthetized 3 times to determine the minimum alveolar concentration (MAC) of halothane in O2 and characterize the anesthetic sparing effect (ie, decrease in MAC of halothane) by xylazine (0.5 mg/kg, i.v.) administration followed immediately by i.v. administration of saline (0.9% NaCI) solution, lo...
Oxender WD, Noden PA, Bolenbaugh DL, Hafs HD.To determine the minimal effective dose of prostagiandin (PGF2alpha; tromethamine salt) given subcutaneously (SC), mares of mixed breeding (400 kg av body weight) were given 2-, 3-, 5-, and 10-mg doses from 7 to 9 days after ovulation. In some but not all mares given doses of 2 and 3 mg of PGF2alpha, luteolysis occurred, but doses of 5 or 10 mg of PGF2alpha were luteolytic in all mares. The 10-mg dose of PGF2alpha did not cause luteolysis in mares 1 day after ovulation, and caused luteolysis in only 2 of 5 mares on day 3 after ovulation. The same dose of PGF2alpha, however, caused luteolysis i...
Schauvliege S, Van den Eede A, Duchateau L, Gasthuys F.Enoximone is a phosphodiesterase III inhibitor frequently used to improve cardiac output (CO) in man. As the use of enoximone has not been reported in horses, the effects of this inodilator were examined in isoflurane anaesthetized ponies. Methods: Prospective, randomised, experimental study. Methods: Six healthy ponies, weighing 286 (212-367) +/- 52 kg, aged 5.0 +/- 1.6 years (4-6.5). Methods: After sedation with romifidine [80 microg kg(-1) intravenously (IV)], general anaesthesia was induced with midazolam (0.06 mg kg(-1) IV) and ketamine (2.2 mg kg(-1) IV) and maintained with isoflurane in...
Ginther OJ.After the cessation of equine embryo mobility (fixation) on mean Day 16, the embryonic vesicle is rotated or oriented so that the pole with the embryo proper is opposite to the mesometrial attachment. Orientation involves massage of the vesicle by contractions of the turgid uterine horn and greater thickening of the vesicle at the pole with the embryo proper. Thickening of the dorsal endometrium (encroachment) especially on each side of the mesometrial attachment accounts for a guitar-pick shape of the vesicle when viewed in cross section of the uterine horn. On Days 21-40, the allantoic sac e...
Brand A, Lindner A, Gerhards H, Valenchon M, Petit O.The objective of this study was to explore how the endurance of five-year-old horses, kept out on pasture all their life and ridden for the first time well into their fifth year of age, developed within one year and compared to that of six-year-old horses raised under the same conditions and to other horses. Horses were submitted to a standardized exercise test (SET) to calculate their v (velocity run under defined conditions inducing 4 mmol/L of blood lactate concentration (LA)) and v (velocity run under defined conditions inducing a heart rate of 180 beats/min). The test consisted of up to ...
Ferrer MS, Canisso IF, Podico G, Ellerbrock RE, Hurley DJ, Palomares R.Different stallions exhibit a high level of variation in the ability of their sperm to survive cryopreservation. A large fraction of stallions show poor post-thaw sperm motility, and their semen is not suitable for commercial freezing. In this study, we hypothesized that the presence of sperm-bound antisperm antibodies (ASAs) was associated with poor cryosurvival of stallion sperm. Our objective was to assess the level of ASA binding to stallion sperm, and determine if it was associated with good or poor sperm cryosurvival. In Experiment 1, cooled shipped semen from 27 stallions was frozen usi...
Pruett HE, Thompson DL, Cartmill JA, Williams CC, Gentry LR.Light horse mares, stallions, and geldings were used to 1) extend our observations on the thyrotropin releasing hormone (TRH) inhibition of GH secretion in response to physiologic stimuli and 2) test the hypothesis that stimulation of endogenous TRH would decrease the normal rate of GH secretion. In Exp. 1 and 2, pretreatment of mares with TRH (10 microg/kg BW) decreased (P < 0.001) the GH response to exercise and aspartate infusion. Time analysis in Exp. 3 indicated that the TRH inhibition lasted at least 60 min but was absent by 120 min. Administration of a single injection of TRH to stal...
Hughes KJ, Rendle DI, Higgins S, Barron R, Cowling A, Love S, Durham AE.Delays between collection and laboratory analysis of equine body fluid samples are common in practice; however, the effects of delays on the accuracy of results and diagnostic interpretation are unknown. Objective: To assess the effects of storage time and temperature combination on protein and cell parameters of equine synovial and mesothelial cavity fluids and determine whether any changes affect clinicopathological interpretation. Methods: In vitro experiment. Methods: Body fluid samples obtained from horses during diagnostic investigation were divided into 7 aliquots and total protein conc...
Braun J, Torres-Boggino F, Hochi S, Oguri N.The objective of this experiment was to examine the effect of seminal plasma on motion characteristics of epididymal and ejaculated equine spermatozoa during storage at 5 degrees C. Epididymal spermatozoa were flushed with either seminal plasma or a skim milk-glucose extender. Ejaculated spermatozoa were collected with extender added 10 minutes after semen collection and addition of extender during ejaculation by placing 50 ml extender in the collection bottle. Semen samples were centrifuged and resuspended with a skim milk-glucose extender containing seminal plasma (0, 5 and 25%; v/v), prepar...
Kutter AP, Bettschart-Wolfensberger R, Schwarzwald CC, Portier KG, Ringer SK.To evaluate the non-calibrated, minimally invasive cardiac output (CO) monitor FloTrac/Vigileo (FloTrac) against thermodilution (TD) CO in standing horses. Methods: Prospective, experimental trial. Methods: Nine adult horses weighing a median (range) of 535 (470-602) kg. Methods: Catheters were placed in the right atrium, pulmonary artery and carotid artery under local anaesthesia. CO was measured 147 times by TD and FloTrac and indexed to body weight. Changes in CO were achieved with romifidine or xylazine and dobutamine constant rate infusions. Bland-Altman analysis, concordance and polar pl...
