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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.
Spontaneous and stimulated adrenocorticotropin and vasopressin pulsatile secretion in the pituitary venous effluent of the horse. Plasma ACTH, arginine vasopressin (AVP), and catecholamines were measured at 5-min intervals in the pituitary venous effluent of the unanesthetized horse. Pulses of ACTH and AVP were found to be surprisingly brief (usually of less than 10-min duration) and frequent (averaging between 15-25 min). A highly significant relationship in the changes in concentration of these two hormones was demonstrated (P less than 0.0002) both at rest and after a mild hypoglycemic stimulus. Although there was also a significant correlation (P less than 0.005) between simultaneous plasma ACTH and AVP values the pu...
Isolation and characterization of three forms of luteinizing hormone from the pituitary gland of the horse. Three isoforms of equine luteinizing hormone (eLH-A, eLH-B and eLH-C) have been isolated from horse pituitary glands. Separation was achieved on the basis of charge heterogeneity by ion-exchange chromatography. These charge differences were apparent after final purification, as determined by electrophoretic mobility on polyacrylamide disc gels (RF = 0.14, 0.19 and 0.26 for eLH-A, -B and -C, respectively). Apparent size differences were also noted between the isohormones by gel filtration on Sephadex G-100. Ve/Vo ratios for eLH-A, -B and -C were 1.72, 1.54 and 1.47, respectively. All 3 isoforms...
Serum concentrations of prolactin, thyroxine and triiodothyronine relative to season and the estrous cycle in the mare. Studies were conducted to characterize circulating concentrations of prolactin, thyroxine (T4) and triiodothyronine (T3) relative to season and the estrous cycle, and to evaluate the ability of thyrotropin-releasing hormone (TRH) to induce prolactin secretion in the horse mare. The increase in serum prolactin following the iv injection of 0, 5, 50 and 500 micrograms TRH was dose-related, while all three doses of TRH induced a significant and comparable increase in serum T4. Seasonal variations in serum prolactin were directly correlated (P less than .001) with changes in photoperiod (r = .80) ...
In vitro interference between equine herpesvirus types 1 and 2. Interference between equine herpesvirus types 1 (EHV-1) and 2 (EHV-2) was studied in equine dermis (ED) monolayer cell cultures and equine lymphocyte cultures. Cell cultures were infected with EHV-2, and after a short incubation period, the cultures were superinfected with EHV-1. At various intervals, different measurements of EHV-1 expression in dually infected cultures, compared with those in cultures infected with EHV-1 alone, were studied. In dually infected ED cell cultures, the EHV-1 cytopathic effect, EHV-1 titer, and EHV-1 enzyme-linked immunosorbent assay antigen titer were maximally ...
Behaviour of the false rig: causes and treatments. The false rig is a castrated horse which shows masculine behaviour of one sort or another. The behaviour patterns reported to the author by owners of such animals and the possible causes are discussed here. Some such horses can show all the behaviour patterns of the entire, including erection and intromission. Evidence is presented that the behaviour is not hormonally induced or hormone dependent. The thesis is put forward that the behaviour shown is part of the normal social interaction between horses and possible treatments are discussed in the light of this possibility.
Guidelines for the recognition and assessment of pain in animals. Prepared by a working party of the Association of Veterinary Teachers and Research Workers. Despite some views to the contrary the working party of the Association of Veterinary Teachers and Research Workers considers that it has been demonstrated that it is possible to prepare guidelines for the recognition and assessment of pain in experimental animals. The detailed information readily available on species specific signs is limited and it has been particularly difficult to obtain such signs for the smaller mammals and for the non-mammalian species.
Symmetry in running. Symmetry plays a key role in simplifying the control of legged robots and in giving them the ability to run and balance. The symmetries studied describe motion of the body and legs in terms of even and odd functions of time. A legged system running with these symmetries travels with a fixed forward speed and a stable upright posture. The symmetries used for controlling legged robots may help in elucidating the legged behavior of animals. Measurements of running in the cat and human show that the feet and body sometimes move as predicted by the even and odd symmetry functions.
Direct demonstration of intrinsic follicle-stimulating hormone receptor-binding activity in acid-treated equine luteinizing hormone. After dissociating equine gonadotropins as a function of time at pH 3, we examined them by radioligand assay and sodium dodecyl sulfate polyacrylamide gel electrophoresis under nondissociating conditions (low, 0.1% SDS). Equine follicle-stimulating hormone (FSH) rapidly lost its receptor-binding activity, and low SDS-polyacrylamide gels demonstrated dissociation into subunits. Maximum dissociation occurred after 20-30 min of pH 3 incubation. Equine luteinizing hormone (LH), however, retained most biologic activity and was largely intact after 72 h of pH 3 incubation. Dose-response curves of ac...
Two-dimensional 1H NMR studies of cytochrome c: assignment of the N-terminal helix. The 1H resonances of 11 sequential amino acids in the N-terminal helix of horse ferrocytochrome c were studied by two-dimensional nuclear magnetic resonance techniques. All the main-chain protons from Lys-5 through Ala-15 and many of the side-chain protons were assigned. J-Correlated spectroscopy (COSY) was used to distinguish protons on neighboring bonds and to recognize amino acid types. Nuclear Overhauser effect spectroscopy (NOESY) was used to define spatially contiguous protons and to determine amino acid sequence neighbors. The relayed coherence experiment (relay COSY) was used to resolv...
Dermal reactivity to histamine, serotonin and bradykinin in relation to allergic skin reactions of the horse. The reactivity of horse skin to intradermal inoculation of histamine, serotonin and bradykinin was investigated, and the resulting reactions compared with those produced in the same horses by a 1% whole-body extract of Culicoides. Both histamine and bradykinin produced large reactions, but there was no significant correlation between the dermal responsiveness to insect allergen and either histamine or bradykinin. Two anti-histamine drugs (promethazine hydrochloride and tripelennamine hydrochloride) were effective in reducing the reaction produced by the insect extract.
Type II diabetes mellitus in a horse. DIABETES mellitus is an uncommon disease in the horse and,
when reported, is frequently secondary to Cushing’s disease
(King, Kavanaugh and Bentinck-Smith 1%2; Loeb, Capen
and Johnson 1966; Tasker, Whiteman and Martin 1966;
Baker and Ritchie 1974; Pauli, Rossi and Straub 1974; Moore,
Steiss, Nicholson and Orth 1979). Diabetes mellitus, associated with chronic pancreatitis, was reported in a horse with
hyperglycaemia, glycosuria and ketonuria (Jeffrey 1969).
Other reported cases were not examined fully to determine the
underlying cause of hyperglycaemia (Jorgenson 1921 ; Wilkinson 195...
Pulmonary function in the horse during anaesthesia: a review. The effect of abnormal body position on cardiovascular and pulmonary function in the awake and anaesthetised horse is reviewed. Parameters such as pulmonary shunt, lung volumes, blood gases and alveolar-arterial oxygen partial pressure differences are discussed. Withholding food for 24 hours and mechanical ventilation may be used to improve blood gas values associated with abnormal recumbency during anaesthesia. During prolonged recovery, horses should be encouraged to adopt sternal recumbency.
Congenital malformation of the large colon causing colic in a horse. An abnormal mesocolic attachment which resulted in a stellate malformation of the left colon adjacent to the pelvic flexure was suspected to be the cause of intermittent episodes of colic in a horse. Resection and side-to-side anastomosis of the large colon at the level of the sternal and diaphragmatic flexures was performed and the horse made an uneventful recovery from surgery. Only minor serum biochemical changes were observed in the initial postoperative period. The abnormal mesocolic attachment was probably a congenital anomaly.
Radiographic anatomy of tendon sheaths and bursae in the horse. Contrast radiography was used to determine the position, shape, relationship and capacity of a number of tendon sheaths and bursae which have clinical significance in the horse. It was possible to establish the normal range of radiographic anatomy for these structures. Some variation in the extent and form of tendon sheaths were found between individual horses and between foals and adults.
Endotoxemia in horses: protection provided by antiserum to core lipopolysaccharide. An equine antiserum to core lipopolysaccharide was produced by inoculation of 6 horses with a boiled cell bacterin made from the J-5 mutant of Escherichia coli O111:B4. The antiserum immunoglobulin G titer to J-5 mutant E coli, as determined by enzyme-linked immunosorbent assay, was 1:15,006. Pooled serum prepared before inoculation (preimmune serum) had a J-5 immunoglobulin G titer of 1:350. The J-5 antiserum was tested for its protective efficacy in sublethal endotoxemia in 14 horses. Four horses served as nontreated controls and were given nothing before endotoxin challenge exposure (10 mic...
Intestinal atresia and stenosis: a review comparing its morphology. A review of the literature on intestinal atresia of domestic animal species and humans was done. The 5 types of intestinal occlusions described in human infants are atresia type 1, atresia type 2, atresia type 3, stenosis, and the "apple peel" or "Christmas tree" deformity. The intestinal defects described in domestic animal species such as the bovine, equine and porcine are similar to those of human infants. The "T-formation", an intestinal defect of the bovine resembling atresia type 3, and rectal stricture, an acquired intestinal defect of the porcine resembling stenosis, were described rec...
Albumin and immunoglobulins G, A and M in aqueous humour from clinically normal equine eyes. The levels of albumin, immunoglobulin G (including IgG [T]), IgA and IgM in the serum and aqueous humour of 47 horses and ponies with no ophthalmic abnormalities were determined by single radial immunodiffusion. There was a linear relationship between serum and aqueous albumin levels. No relationship of serum and aqueous IgG levels was observed. IgA was detected in only one aqueous sample. IgM was not detected in aqueous humour from any eye in this study. The factors which may influence albumin and immunoglobulin levels in normal aqueous humour are discussed.
Role of conceptus secretory products in establishment of pregnancy. Conceptuses produce steroids, prostaglandins, proteins and possibly other unidentified agents which may play a role in the establishment and maintenance of pregnancy. A key event in this process is protection of the corpus luteum (CL) from the luteolytic activity of prostaglandin (PG) F-2 alpha of uterine origin. Oestrogens produced by the pig conceptuses between Days 11 and 16 appear to exert an antiluteolytic effect resulting in the sequestering of PGF-2 alpha within the uterine lumen. Failure of the pregnant uterus to release PGF-2 alpha in an endocrine fashion, therefore, allows for mainte...
Impaired estrogen production by Leydig cells of the naturally retained testis in unilaterally cryptorchid boars and stallions. Estrogen production in vitro was compared for Leydig cells from cryptorchid and scrotal testes in boars and stallions. Animals with natural and experimental cryptorchidism were used. Purified Leydig cells were prepared from testes of mature animals by collagenase treatment and Percoll density gradients. After incubation for 3 hours (1 X 10(6) cells), estrone sulfate and estrone in the media were measured by direct radioimmunoassay. Androstenedione and testosterone in media extracts also were determined. Cells from the abdominal testis of unilateral cryptorchid boars and stallions showed impair...
Effects of flunixin meglumine, phenylbutazone and a selective thromboxane synthetase inhibitor (UK-38,485) on thromboxane and prostacyclin production in healthy horses. The efficacy of three agents which alter the metabolism of arachidonic acid was investigated in normal, conscious horses. A dose response evaluation was made of flunixin meglumine and phenylbutazone, two cyclo-oxygenase inhibitors, and of a selective thromboxane synthetase inhibitor, UK-38,485. Radioimmunoassay of thromboxane B2 (TxB2) and 6-keto prostaglandin F1 alpha (PGF1 alpha) was used to assess the concentrations of thromboxane A2 (TxA2) and prostacyclin (PGI2) respectively, in serum. Flunixin was the most potent inhibitor of serum TxB2 and 6-keto PGF1 alpha production. UK-38,485 also de...
Intravenous acid infusion without lowering arterial pH stimulates breathing. The aim of this study was to determine whether increases in ventilation would occur during intravenous acid infusion even if systemic arterial pH was held constant. In six awake ponies, HCl (500 ml, approximately 0.312 M) was infused into the right atrium at a total dose of 1.0 meq/kg over 18 min while an equivalent dose of NaOH was infused into the left heart to restore systemic arterial pH to normal. Total ventilation increased at the onset of the infusion and remained elevated although systemic arterial pH was normal to slightly alkaline. The increase in ventilation during the initial 2 min...
Equine intravenous glucose tolerance test: glucose and insulin responses of healthy horses fed grain or hay and of horses with pituitary adenoma. Intravenous glucose tolerance testing (0.5 g/kg of body weight) was done on 2 groups of healthy horses maintained with hay (group 1, n = 5) and with hay plus grain supplementation (group 2, n = 5) and on a group of horses with clinically diagnosed pituitary adenoma (group 3, n = 10). Healthy horses showed an immediate increase of plasma glucose concentration after the IV glucose injection, with return of values to base line in 1 hour. Group 3 horses showed resting hyperglycemia and a delayed return of glucose values to base line (3 hours). Group 3 horses showed resting hyperinsulinemia and a f...
A new approach to quantification of Sertoli cells that avoids problems associated with the irregular nuclear surface. A new approach to quantification of Sertoli cells is described. The number of Sertoli cells per testis was calculated from the number of spermatids per testis, the number of spermatids per Sertoli cell apex, and the correction for the lifespan of spermatids enumerated per testis. To evaluate this method under different physiological conditions, testes from 28 adult (4-20-year) stallions obtained in the nonbreeding season (December-January) and from 28 adult stallions in the breeding season (June-July) were compared. Number of Sertoli cells per gram parenchyma was similar between seasons. Howev...
Glucose tolerance and insulin sensitivity in ponies and Standardbred horses. The existence of an innate insulin insensitivity in ponies was investigated and compared with the situation in larger breeds of horse. Ponies that were fat or had previously suffered laminitis were found to be far more intolerant to oral glucose loading (1 g/kg bodyweight [bwt]) than normal ponies or Standardbreds. These ponies also exhibited a far greater response in plasma insulin levels after glucose loading. Insulin response tests (0.4 iu/kg bwt insulin intravenously) showed only a minimal and very protracted response in both the fat and laminitic groups. The relevance of these findings in...
Relationship between spinal biomechanics and pathological changes in the equine thoracolumbar spine. The relationship between spinal biomechanics and pathological changes occurring in functionally normal equine thoracolumbar spines was studied in 23 horses. Ventrolateral vertebral body osteophytes occurred in 36 per cent of the spines. The majority occurred between the 10th and 17th thoracic vertebrae with the largest being found between the 11th and 13th thoracic vertebrae, the region of the thoracic spine where the greatest amount of lateral bending and axial rotation occurs. Impingement of the dorsal spinous processes was detected in 86 per cent of the spines with most lesions occurring be...
