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Topic:Physiology
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.
Absorption of bovine colostral immunoglobulins G and M in newborn foals. The uptake of colostral IgG and IgM, their serum half-lives, and the rates of endogenous synthesis of IgG and IgM were evaluated in 6 newborn foals fed bovine colostrum (principals) and 6 foals allowed to suckle their dams (controls). The principal foals were fed 400 ml of bovine colostrum (IgG, 10,000 mg/dl and IgM, 200 mg/dl) at 2-hour intervals, from 2 to 20 hours after foaling (total dose, 4 L). Serum IgG and IgM concentrations were determined by single radial immunodiffusion from birth to 98 days of age. At foaling, principal foals had no detectable serum equine IgG, but 1 control foal ha...
Variations of serum vitamin E, cholesterol, and total serum lipid concentrations in horses during a 72-hour period. Fluctuations of serum vitamin E (alpha-tocopherol), cholesterol, and total lipids were monitored in 12 horses at 3-hour intervals for 72 hours. Mean coefficients of variation were 12, 5, and 15%, respectively. Statistical analyses were used to conclude that instrumentation error was accountable for only a small portion of the vitamin E variation. Results indicated that a single serum sample assay is an unsatisfactory indicator of vitamin E status in horses. These data have clinical application in the evaluation of horses suspected to be affected with equine degenerative myeloencephalopathy. Th...
Prostaglandin production by horse embryos and the effect of co-culture of embryos with endometrium from pregnant mares. Embryos, endometrial biopsies, and uterine lavage fluid were collected from pregnant and non-pregnant mares 14 days after ovulation. Embryos were cultured for 20.5 h with and without endometrial tissue from pregnant mares, and endometrial tissue was cultured alone. Endometrial content of PGF tended to be higher (P = 0.06) in non-pregnant than in pregnant mares, but the amount of PGF released from tissue during culture was similar for pregnant and non-pregnant mares. Lavage fluid from non-pregnant mares also tended (P = 0.08) to contain higher concentrations of PGF. Coincubation of embryos with...
Effect of surgical manipulation, placental fluid, and flunixin meglumine on fetal viability and prostaglandin F2 alpha release in the gravid uterus of mares. Twenty-one pregnant mares with single or twin conceptuses between 41 and 65 days of gestational age were allotted to 5 treatment groups. A ventral median celiotomy was performed in all mares. In group-1 mares (3 mares, single conceptus), the uterus and fetus were palpated for 5 minutes. In group-2 mares (3 mares, single conceptus, flunixin meglumine), 250 ml of sterile placental fluid was injected into the nongravid uterine horn. In group-3 mares (4 mares, unicornuate twin conceptuses), group-4 mares (3 mares, unicornuate twin conceptuses, flunixin meglumine), and group-5 mares (8 mares, bicor...
Large intestinal capacity, retention times, and turnover rates of particulate ingesta associated with extensive large-colon resection in horses. Fecal excretion of a particulate marker, ytterbium (Yb), was evaluated in 9 horses before surgery and 3 weeks, 3 months, and 6 months (4 trials) after sham-operation (group 1; n = 3) or extensive large colon resection (group 2; n = 6). Fecal excretion curves of total Yb excretion, loge Yb excretion, % Yb excretion, loge % Yb excretion, and cumulative % Yb excretion were evaluated, and kinetic analysis was performed on the loge Yb excretion curves to detect mixing pools and to calculate the fractional rate of particulate passage, turnover rate, and pool size. Calculations were performed to dete...
The effect of endometrial biopsy on ovulatory interval in mares. Luteolysis with subsequent shortening of diestrus has been reported to follow equine endometrial biopsy performed early in the luteal phase of the estrous cycle, but a comprehensive study of the effect of endometrial biopsy on cycle length at different times of the cycle has not been reported. In this study, endometrial biopsies were obtained from four different pony mares on each of Days 0, 4, 8, 12, 16 and 20 after ovulation as determined by serial palpation per rectum. Compared with control cycles in the same mares, the ovulatory interval was shortened in mares from which biopsies were obta...
Complement activity and selected hematologic variables in newborn foals fed bovine colostrum. Serum complement activity and selected hematologic variables were evaluated in 5 newborn foals fed bovine colostrum (principal group) and 6 foals allowed to nurse their dam (control group). Also, bovine colostrum was evaluated for anti-equine antibodies. Precolostral serum hemolytic and conglutinating complement activities were low and increased similarly in foals of both groups to reach adult values between 1 and 3 weeks after birth. Bovine colostrum strongly agglutinated, but did not hemolyse principal foals' RBC and blood containing all known equine blood group alloantigens. Hemolysis was n...
Response of equine airway smooth muscle to acetylcholine and electrical stimulation in vitro. Smooth muscle strips from the midcervical portion of the trachea and bronchial smooth muscle strips from third-generation airways of horses were placed in tissue baths, and isometric contractile force was measured. Active force was measured in response to electrical stimulation and exogenous acetylcholine. Square-wave electrical stimuli were applied at various voltages (10, 12, 15, 18, 20, 25 V), frequencies (3, 5, 10, 15, 20, 25, 30 Hz), and pulse durations (0.2, 0.5, 1.0, 1.5, 2.0 ms). Isometric contractile force increased as voltage, frequency, and pulse duration increased. Maximal contract...
High frequency jet ventilation in horses: an experimental study. High frequency jet ventilation (HFJV) is a recently developed mode of ventilation that delivers small tidal volumes at frequencies greater than 60 cycles per min via an injection catheter to the animal's airway. The construction of a high frequency jet ventilator suitable for use in adult horses is described. The effectiveness of this ventilator in maintaining normal arterial blood-gas tension was evaluated in five healthy adult horses. The horses were anaesthetised with intravenous acetylpromazine, guaifenesin, and thiamylal, positioned in lateral recumbency and baseline measurements were mad...
Culture of equine trophoblastic vesicles in vitro. Trophoblastic vesicles have been used to study early embryonic development and maternal recognition of pregnancy in domestic animals. The purpose of this study was to characterize the formation of trophoblastic vesicles from Day-12 to Day-16 equine conceptuses. Conceptuses (n = 19) were collected nonsurgically from mares, the capsule was removed, and the conceptus (trophoblast and inner cell mass) was dissected into 2- to 4-mm fragments. Conceptus fragments were cultured in either Ham's F10 (HF10) or Minimum Essential Media (MEM) with 10% fetal bovine serum (FBS) in 24-well plates. Plates were...
Cardiovascular effects recorded in horses during anaesthesia after treatment with trichlorfon. Five horses were anaesthetised twice with thiopentone sodium, guaifenesin and halothane. The second anaesthesia was 16 days after the first and two days following oral administration of trichlorfon. Heart rate, carotid arterial, pulmonary arterial and right atrial pressures, cardiac output and blood temperature were measured every 15 minutes for 120 minutes. Heart rate, carotid arterial pressure and cardiac output were similar on both occasions. Pulmonary arterial and right atrial pressures were highest during anaesthesia after treatment with trichlorfon when compared with values obtained befo...
Radioimmunoassay of inhibin in various mammals. A sensitive radioimmunoassay (RIA) for the determination of inhibin in peripheral plasma and tissue homogenates of different species has been developed using antisera to partially purified bovine follicular fluid (bFF) inhibin and 125I-labelled bFF 32 kDa inhibin. Antisera were produced by immunization of rabbits with partially purified bFF inhibin prepared by immunoaffinity chromatography. Increasing doses of a high titre antiserum could neutralize the suppressing effect of bFF, porcine follicular fluid and rat ovarian homogenate on FSH secretion from rat anterior pituitary cells in culture. ...
Postanesthetic compartmental syndrome in a horse. After surgery, high intramuscular pressures were measured in a horse with clinical signs of postanesthetic myopathy that developed following a 2.25-hour surgical procedure. In the postoperative period, tests for muscular and neurologic integrity were made, including measurement of intracompartmental muscle pressure.
An ongoing in vivo immune response affects the abundancy and differentiation of lymphokine-activated killer cell precursors, but does not influence their broad spectrum target reactivity. Using a model of local lymph node (LN) immunization, we investigated the effect of in vivo Ir on the generation of lymphokine-activated killer (LAK) cells or their precursors. Ag used for immunization were SRBC, horse RBC, OVA, keyhole limpet hemocyanin, or CFA. Ag-draining LN, in the acute phase of the Ir, did not contain detectable LAK effector activity, nor an enhanced NK activity. After culture for 3 to 5 days in the absence of exogenously added IL-2, immunized LN cells developed a spontaneous LAK-like cytotoxicity. This activity represented a substantial fraction of the IL-2-generated LAK...
Effect of oral L-carnitine on its concentration in the plasma of yearling Thoroughbred horses. After an oral dose of 10 g of L-carnitine the plasma concentrations of free and total carnitine increased in five yearling thoroughbred horses, reaching a peak two to four hours after administration, but in two horses there was no increase. In the five which responded, the mean (+/- sd) peak increase in total carnitine concentration was 15.1 +/- 6.9 mumol/litre from a predose mean of 18.8 +/- 3.4 mumol/litre, and the mean peak increase in free carnitine concentration was 13.5 +/- 3.1 mumol/litre from a pre-dose mean concentration of 12.5 +/- 2.2 mumol/litre. These changes were similar to those...
Effect of weight loading on the coronary band interstitial fluid pressure in horses. Interstitial fluid pressures, as a possible function of limb load, were measured at 2 sites within the digital coronary dermis of both cranial digits in 10 standing horses. Fluid pressure changes and digital load measurements were simultaneously detected and recorded by use of, respectively, modified wick-in-needle and force plate transducers coupled to a microcomputer. Mean pressures, recorded at limb loads between 50 and 80 kg, were 2.29 +/- 3.17 mm of Hg at the toe and 2.49 +/- 5.91 mm of Hg at the heel. Mean pressures, recorded between 150 and 180 kg, were 5.01 +/- 5.23 mm of Hg at the toe...
Blood gas measurements during exercise: errors due to temperature correction. This study assessed the degree to which correcting blood gas measurements to rectal temperature (Tre) rather than to the temperatures at which gas exchange occurs [pulmonary arterial (Tpa) or intramuscular (Tm)] introduces errors into blood gas analysis of exercising mammals. Horses and steers weighing 450 kg were run on a treadmill at speeds up to those eliciting maximal rates of O2 consumption (VO2max), and temperatures were measured in various body compartments. In both species Tpa rose faster than Tre during the run, the degree of dissociation being a function of exercise intensity and dur...
Normal intestinal motility. Perhaps because of the inherent difficulty in using horses as experimental animals, only a relatively small amount of data is as yet available regarding normal equine gut motility. However, it is clear that the horse is fundamentally similar to other mammalian species studied. The neural and humoral control of gut activity requires much exploration; it is likely that, in the horse, some of this information will be derived during the investigation of the effects of various substances that might have clinical relevance. This is alluded to in the chapter that follows (The Effects of Pharmacologic...
[Seasonal changes in blood testosterone in the Giara horse]. The blood testosterone changes in three Giara stallions, average age 8 years old and average weight 183 Kgs, were checked weekly for a year using a radioimmunological method. The horses showed a highly seasonal hormonal activity concentrated in the first half of the year (winter and spring). In the second half of the year (summer and fall) the stallions showed low levels of testosterone. The highest level of the androgen hormone occurred in April, the lowest in October. The absolute levels of this hormone agreed substantially with the relative literature.
Inertance of the respiratory system in ponies. The purpose of the present work was to measure the pulmonary inertance (IL) in ponies and to analyze its potential influence on the mechanics of breathing and on their aptitude to increase ventilation during exercise. Five healthy ponies 2.4-4 yr old [mean wt 255 +/- 15 (SE) kg] were used. On the one hand, inertance of the respiratory system (Irs) was computed from the value of the resonant frequency (fr) measured by the forced oscillation technique. On the other hand, respiratory airflow, tidal volume (VT), and transpulmonary pressure (PL) changes were recorded while the ponies were performin...
Oxygen transport during exercise in large mammals. I. Adaptive variation in oxygen demand. This study investigated mechanisms used by horses and steers to increase O2 uptake and delivery (VO2) from resting to maximal rates and identified the mechanisms that enable horses to achieve higher maximal rates of O2 consumption (VO2max) than steers. VO2 and circulatory variables were measured while Standardbred trotting horses and steers (450-kg body mass) stood quietly and ran on a treadmill at speeds up to those eliciting VO2max. As VO2 increased in both species, heart rate and circulating hemoglobin (Hb) concentration increased, thereby increasing O2 delivery by the circulation, while ca...
Characterization of plasma progesterone concentrations for two distinct luteal morphologies in mares. Plasma progesterone concentrations in mares were determined in two experiments during the time that the luteal glands were detectable by transrectal ultrasonography. In both experiments, corpora lutea were classified into two types of morphologies based on their ultrasonic appearance: centrally nonechogenic luteal glands (fluid-filled) and uniformly echogenic luteal glands (non-fluid-filled). In Experiment 1, daily blood samples were taken from horse mares during August through October and May through July. There were no significant effects of season or luteal morphology on progesterone concen...
Oxygen transport during exercise in large mammals. II. Oxygen uptake by the pulmonary gas exchanger. Because the maximal rate of O2 consumption (VO2max) of the horse is 2.6 times larger than that of steers of equal size, we wondered whether their pulmonary gas exchanger is proportionately larger. Three Standardbred racehorses [body mass (Mb) = 447 kg] and three domestic steers (Mb = 474 kg) whose cardiovascular function at VO2max had been thoroughly studied (Jones et al. J. Appl. Physiol. 67: 862-870, 1989) were used to study their lungs by morphometry. The basic morphometric parameters were similar in both species. The nearly 2 times larger lung volumes of the horses caused the gas exchange ...
Effects of a draft-loaded interval-training program on skeletal muscle in the horse. Five Standardbred trotters were trained on a treadmill 3 times/wk for 12 wk by intervals of draft-loaded exercise. The draft load was 34 kp and the velocity approximately 7 m/s. Muscle biopsies were taken from the gluteus medius and longissimus muscles before training and after 2, 4, 8, and 12 wk of training and from the brachiocephalicus muscle before and after training. Both the percentage and the area of type IIa fibers increased and the percentage of type IIb fibers decreased in the gluteus medius muscle during the first 2 wk of training, and then no further significant difference was note...
Gas conductance during high-frequency oscillatory ventilation in large animals. Three sheep, a foal, a pony, and a calf were anesthetized and ventilated for short periods, using a high-frequency oscillatory ventilator. The efficiency of CO2 elimination was characterized at various oscillatory frequencies (50 to 30 Hz) and various tidal volumes, although the tidal volume used was always less than the measured dead space of the animal. In general, increasing either the oscillatory frequency or tidal volume increased CO2 elimination, but increasing the tidal volume had more effect. The relationship between these 3 variables was best described by a power law equation. Ventila...
Effects of pharmacological agents on gastrointestinal motility. The control mechanisms of gastrointestinal motility are complex. Extrinsic neurohormonal effects modulate an intrinsic system, often called the "gut brain," composed of nervous and neuropeptide components. To exert pharmacologic influence on GI motility, use is made of agents that mimic the external control system. Agents that stimulate opioid receptors, block adrenoceptors, block or facilitate acetylcholine action, or antagonize the action of prostaglandins are used to effect changes in GI motility. The major indications for pharmacologic intervention are to increase motility in constipation,...
Evaluation of the opsonic capacity of core lipopolysaccharide antiserum of equine origin against smooth Escherichia coli 0111:B4, using macrophage chemiluminescence. A study was performed to determine whether equine antiserum to core lipopolysaccharide (LPS) would enhance phagocytosis of smooth gram-negative (GN) organisms by equine macrophages. Five healthy adult horses (group A) were immunized with a bacterin prepared from the J-5 mutant of Escherichia coli 0111:B4 and Salmonella minnesota R595 to produce antibodies to core LPS. Five horses (group B) served as nonimmunized controls and were given physiologic saline solution instead of the rough mutant bacterin. Serum antibody titers to core LPS and to smooth E coli 0111:B4 were determined by indirect ELI...
Intestinal healing and methods of anastomosis. Optimal intestinal healing occurs when like layers of the intestinal wall are aligned. Hand-sewn, double-layer, end-to-end anastomosis that apposes the mucosa and produces slight inversion of the seromuscular layer is recommended to minimize adhesion formation and provide reasonable alignment of the intestinal layers. Stapled, everted, triangulated, end-to-end anastomosis is not recommended because of extensive adhesion formation and poor healing of the intestinal layers. The preferred stapled techniques create an inverting, side-to-side stoma between the bowel segments.
Release of immunoreactive arachidonate metabolites by equine endometrium in vitro. The ability of equine endometrium to release prostaglandin (PG) F, PGE2, and leukotriene (LT) B4 was studied in vitro, using endometrial tissue from diestrous mares. Because of the high cross-reactivity of the PGF antiserum with PGF1 alpha and with PGF2 alpha, results were quoted as total immunoreactive PGF. Significant concentrations of these arachidonate metabolites were released into tissue culture medium between 1 and 24 hours of incubation. Significantly higher concentrations of PGE, but not of PGE2 or LTB4, were released from endometria of mares with chronic endometritis than from genita...
