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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.
T-cell tolerance to the developing equine conceptus. One of the most intriguing and dramatic examples of immunological tolerance is displayed by the mammalian foetal-placental unit, which thrives as a semi-allograft in the mother's uterus during pregnancy. The success of the so-called foetal allograft stands in stark contrast to the failure of most tissue and organ grafts to survive without genetic matching of donor and recipient or drastic immunosuppression of the recipient's immune system. Experiments conducted over the past 60 years have revealed multiple mechanisms that enable the conceptus to avoid immunological detection or destruction. Ma...
Effects of a constant-rate infusion of dexmedetomidine on the minimal alveolar concentration of sevoflurane in ponies. Dexmedetomidine has been administered in the equine as a constant-rate infusion (CRI) during inhalation anaesthesia, preserving optimal cardiopulmonary function with calm and coordinated recoveries. Inhalant anaesthetic sparing effects have been demonstrated in other species, but not in horses. Objective: To determine the effects of a CRI of dexmedetomidine on the minimal alveolar concentration (MAC) of sevoflurane in ponies. Methods: Six healthy adult ponies were involved in this prospective, randomised, crossover, blinded, experimental study. Each pony was anaesthetised twice (3 weeks washou...
The emerging pathophysiology of age-related testicular degeneration with a focus on the stallion and an update on potential therapies. Studies in laboratory rodents are shedding light on the pathophysiology of testicular ageing and now suggest a complicated basis for age-related declines in testicular function. A highly significant contributor to infertility may involve failure of specific and complex testicular microenvironments (niches) comprised of a variety of cellular and molecular components. Our laboratory has applied testis tissue xenografting to the study of testicular ageing in the stallion. Using this technique, we have confirmed that the disease is tissue autologous. As would be expected from a tissue autologous d...
Canine hepacivirus NS3 serine protease can cleave the human adaptor proteins MAVS and TRIF. Canine hepacivirus (CHV) was recently identified in domestic dogs and horses. The finding that CHV is genetically the virus most closely related to hepatitis C virus (HCV) has raised the question of whether HCV might have evolved as the result of close contact between dogs and/or horses and humans. The aim of this study was to investigate whether the NS3/4A serine protease of CHV specifically cleaves human mitochondrial antiviral signaling protein (MAVS) and Toll-IL-1 receptor domain-containing adaptor inducing interferon-beta (TRIF). The proteolytic activity of CHV NS3/4A was evaluated using ...
Comparison of the fecal microbiota of healthy horses and horses with colitis by high throughput sequencing of the V3-V5 region of the 16S rRNA gene. The intestinal tract houses one of the richest and most complex microbial populations on the planet, and plays a critical role in health and a wide range of diseases. Limited studies using new sequencing technologies in horses are available. The objective of this study was to characterize the fecal microbiome of healthy horses and to compare the fecal microbiome of healthy horses to that of horses with undifferentiated colitis. A total of 195,748 sequences obtained from 6 healthy horses and 10 horses affected by undifferentiated colitis were analyzed. Firmicutes predominated (68%) among health...
Effects on cardiopulmonary function and oxygen delivery of doses of romifidine and xylazine followed by constant rate infusions in standing horses. The objective of this study was to compare the cardiopulmonary effects of a xylazine or romifidine loading-dose, followed by a constant rate infusion (CRI) of the same α(2)-agonist. Nine research horses were treated in a randomized, blinded, crossover design with xylazine or romifidine. After instrumentation, a loading dose of intravenous xylazine (1mg/kg) or romifidine (80μg/kg) was administered, immediately followed by a CRI of xylazine (0.69mg/kg/h) or romifidine (30μg/kg/h) for a duration of 2h. Cardiopulmonary variables were recorded before bolus administration, during CRI, and for 1h ...
Calcium-calmodulin and pH regulate protein tyrosine phosphorylation in stallion sperm. The mechanisms leading to capacitation in stallion sperm are poorly understood. The objective of our study was to define factors associated with regulation of protein tyrosine phosphorylation in stallion sperm. Stallion sperm were incubated for 4 h in modified Whitten's media with or without bicarbonate, calcium, or BSA. When sperm were incubated in air at 30×10⁶/ml at initial pH 7.25, protein tyrosine phosphorylation was detected only in medium containing 25 mM bicarbonate alone; calcium and BSA inhibited phosphorylation. Surprisingly, this inhibition did not occur when sperm were incubate...
Effects of intra-articular sodium pentosan polysulfate and glucosamine on the cytology, total protein concentration and viscosity of synovial fluid in horses. Evaluate synovial fluid cytology, total protein concentration and viscosity after intra-articular administration of combined pentosan polysulfate and glucosamine in horses. Methods: Ten adult Standardbred horses had each carpal joint (n = 20) randomly assigned to one of two treatments: control (5 mL saline) or treated (pentosan polysulfate and glucosamine). All horses received an intra-articular injection every 7 days for 3 weeks and synovial fluid samples were collected on days 1 (baseline), 2, 3, 7, 8, 9, 14, 15, 16 and 21. Synovial fluid variables measured included total protein concentrati...
Caseinate protects stallion sperm during semen cooling and freezing. Extenders with a defined composition containing only components with clearly protective effects on sperm during storage would be an advantage. The aims of the present work were to assess whether caseinate, improves cooled and frozen equine semen quality. Semen from six stallions were suspended with four different cooling extenders C1) Kenney extender; C2) 0.6 % caseinate; C3) 2.7 % caseinate ; and C4) C1 + 2.1 % caseinate, and frozen extenders: F1) INRA 82 extender; F2) 1.35 % caseinate; and F3) 2.7 % caseinate. Although there was no significant difference between the motility rate among the c...
Cardiac troponin I in racing standardbreds. Upper reference limits for cTnI have not been established for healthy Standardbred racehorses. Objective: To establish cTnI upper reference limits for Standardbred racehorses and determine if increases in plasma cTnI concentration can be detected in 1-2 hours after a race. Methods: Samples were obtained from 586 apparently healthy Standardbreds aged 2-14 years before racing and from the winners of 144 races 1-2 hours after the end of the race. Methods: Prospective, observational study; convenience sampling; assay validation; and reference limits determinations were performed according to ASCVP...
Ovarian and PGF2α responses to stimulation of endogenous PRL pulses during the estrous cycle in mares. The effects of a PRL-stimulating substance (sulpiride) on PRL and PGF2α secretion and on luteal and ovarian follicular dynamics were studied during the estrous cycle in mares. A control group (n = 9) and a sulpiride group (Sp; n = 10) were used. Sulpiride (25 mg) was given every 8 h from Day 13 postovulation to the next ovulation. Repeated sulpiride treatment did not appear to maintain PRL concentrations at 12-h intervals beyond Day 14. Therefore, the hypothesis that a long-term increase in PRL altered luteal and follicular end points was not testable. Hourly samples were collected from the h...
Effects of oral treatment with N-acetylcysteine on the viscosity of intrauterine mucus and endometrial function in estrous mares. Persistent breeding-induced endometritis is ranked as the third most common medical problem in the adult mare and leads to enormous economic loss in horse breeding. In mares suffering from persistent breeding-induced endometritis, increased amounts of intrauterine (i.u.) fluid or viscous mucus in estrus or after breeding may act as a barrier for sperm and can contribute to low fertility. Current therapies of these mares aim to eliminate i.u. fluid and mucus by uterine lavage and/or administration of ecbolic drugs. Recently, i.u. administration of N-acetylcysteine (NAC) has been shown to suppor...
Novel link between inflammation and impaired glucose transport during equine insulin resistance. Although insulin resistance (IR) has been increasingly recognized in horses, a clear understanding of its pathophysiology is lacking. The purpose of the present study was to determine the early pathologic changes in IR horses by characterizing alterations in proteins that play key roles in innate immunological responses and inflammatory pathways, and by identifying potential links with glucose transport and insulin signaling. Visceral (VIS) and subcutaneous (SC) adipose tissue and skeletal muscle (SM) biopsies were collected from horses, which were classified as insulin-sensitive (IS) or IR ba...
Laminar regulation of STAT1 and STAT3 in black walnut extract and carbohydrate overload induced models of laminitis. STAT1 and STAT3 are important signaling molecules in disorders of systemic inflammation and are likely to be involved in laminitis, as laminar and systemic inflammation have been well documented in experimental models of laminitis. Objective: The STAT1 and STAT3 activation (via phosphorylation of tyrosine and serine moieties) is occurring in the laminar tissue during the developmental and onset of lameness time points in both the black walnut extract (BWE) and carbohydrate overload (CHO) models of laminitis. Methods: Archived laminar tissue from horses. Methods: Experimental studies of induced...
Equine cloning: in vitro and in vivo development of aggregated embryos. The production of cloned equine embryos remains highly inefficient. Embryo aggregation has not yet been tested in the equine, and it might represent an interesting strategy to improve embryo development. This study evaluated the effect of cloned embryo aggregation on in vitro and in vivo equine embryo development. Zona-free reconstructed embryos were individually cultured in microwells (nonaggregated group) or as 2- or 3-embryo aggregates (aggregated groups). For in vitro development, they were cultured until blastocyst stage and then either fixed for Oct-4 immunocytochemical staining or maint...
Plasma clearance and half-life of prostaglandin F2alpha: a comparison between mares and heifers. Horses are about five times more sensitive to the luteolytic effect of prostaglandin F2alpha (PGF) than cattle, as indicated by a recommended clinical dose of 5 mg in horses and 25 mg in cattle. Novel evaluations of the PGF plasma disappearance curves were made in mares and in heifers, and the two species were compared. Mares and heifers (n = 5) of similar body weight were injected (Min 0) intravenously with PGF (5 mg per animal). Blood was sampled every 10 sec until Min 3, every 30 sec until Min 5, every 10 min until Min 60, and every 30 min until Min 240. The mean PGF concentration was great...
Farriery for the hoof with a sheared heel. Sheared heels develop as an adaptation-distortion of the hoof capsule as a result of an abnormal strike and loading pattern of the foot, which is generally a consequence of limb conformation. The growth rate around the circumference of the hoof should be approximately uniform, but regional disturbances in growth rate can occur to either increase or decrease growth. The primary conformational trait that is observed in horses that develop sheared heels is a rotational deformity of the distal limb and a narrow chest. Farriery is directed toward improving the hoof capsule distortion and decreasing...
Temperature regulation in horses during exercise and recovery in a cool environment. Clipping the winter coat in horses is done to improve heat dissipation during exercise and make grooming easier. It is often combined with blanketing to keep the horse warm. The aims of the present study were to investigate how clipping and the use of blankets affect thermoregulation during exercise and recovery in horses. Methods: One Gotland pony, one New Forest pony, and one warm-blooded horse exercised one after the other on a 6450 m long track. The horses walked, trotted and cantered according to a predetermined scheme, which took about 50 minutes including three stops. The scheme was rep...
Macrophage migration inhibitory factor is expressed by equine conceptuses and endometrium. Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine expressed by a wide range of tissues, which has been implicated to be involved in reproduction. Relative abundance of MIF mRNA in conceptus and endometrial tissue was assessed using real-time RT-PCR. Western blot analysis and immunohistochemistry were used to detect MIF protein expression. MIF transcript abundance was lowest in conceptuses obtained 16 days after ovulation, while the remaining stages of conceptus development that were analysed showed relatively constant expression levels. Migration inhibitory factor expressi...
Forces and pressures on the horse’s back during bareback riding. The objectives of this study were to measure forces and pressure profiles when riding with a conventional saddle compared to bareback riding. An electronic pressure mat was used to compare contact area, mean total force and pressure variables for one rider riding seven horses at sitting trot with a conventional saddle or bareback. The use of a saddle was associated with a larger contact area and higher mean total force compared with the bareback condition. Mass normalized mean total force for bareback riding was lower than expected based on the rider's body mass, suggesting that shear forces e...
Measurement of tidal volume using respiratory ultrasonic plethysmography in anaesthetized, mechanically ventilated horses. To compare tidal volume estimations obtained from Respiratory Ultrasonic Plethysmography (RUP) with simultaneous spirometric measurements in anaesthetized, mechanically ventilated horses. Methods: Prospective randomized experimental study. Methods: Five experimental horses. Methods: Five horses were anaesthetized twice (1 week apart) in random order in lateral and in dorsal recumbency. Nine ventilation modes (treatments) were scheduled in random order (each lasting 4 minutes) applying combinations of different tidal volumes (8, 10, 12 mL kg(-1)) and positive end-expiratory pressures (PEEP) (0,...
The analysis of densitometric and geometric parameters of bilateral proximal phalanges in horses with the use of peripheral quantitative computed tompgraphy. Proximal phalanges in horses are among bones that are most prone to injuries. So far, the detailed analysis of densitometric and geometric parameters of both front legs proximal phalanges in horses has not been investigated. The aim of this study was to compare the densitometric and geometric parameters between proximal phalanges in equine both front legs with the use of peripheral quantitative computed tomography (pQCT). Methods: The study material comprised isolated both front legs proximal phalanges derived from 22 horses. The structure analysis of the proximal phalanges was conducted with ...
A pilot study on the corneal curvatures and ocular dimensions of horses less than one year of age. Intraocular lenses (IOLs) have been implanted in adult equine eyes after cataract surgery. Foals and weanlings comprise a large proportion of those horses undergoing cataract surgery. Due to potential differences in the size and corneal curvature of the juvenile eye, it is not currently known whether implantation of adult IOLs is appropriate in foals and weanlings. The objective of the study was to measure the anterior chamber depth (ACD), central lens thickness (CLT), vitreous chamber depth (VCD), axial globe length (AGL) and corneal curvature of horses less than one year of age. The axial di...
Stallion spermatozoa selected by single layer centrifugation are capable of fertilization after storage for up to 96 h at 6°C prior to artificial insemination. One of the challenges faced by equine breeders is ensuring delivery of good quality semen doses for artificial insemination when the mare is due to ovulate. Single Layer Centrifugation (SLC) has been shown to select morphologically normal spermatozoa with intact chromatin and good progressive motility from the rest of the ejaculate, and to prolong the life of these selected spermatozoa in vitro. The objective of the present study was a proof of concept, to determine whether fertilizing ability was retained in SLC-selected spermatozoa during prolonged storage. Results: Sixteen mares were insemi...
The proximal aspect of the suspensory ligament in the horse: How precise are ultrasonographic measurements? To evaluate intra- and interobserver variability in ultrasonographic measurements of the proximal aspect of the suspensory ligament (PSL) in the horse. Objective: A minimum difference of ≥20% is required to differentiate reliably between physiological and pathological alterations related to dimensions. Methods: Two operators examined the PSL in all 4 limbs of 14 horses twice using different techniques and different probes with and without standoff pads. Measurements were taken from the longitudinal and transverse images. Inter- and intraoperator variability was evaluated using agreement indi...
Similar slow down in running speed progression in species under human pressure. Running speed in animals depends on both genetic and environmental conditions. Maximal speeds were here analysed in horses, dogs and humans using data sets on the 10 best performers covering more than a century of races. This includes a variety of distances in humans (200-1500 m). Speed has been progressing fast in the three species, and this has been followed by a plateau. Based on a Gompertz model, the current best performances reach 97.4% of maximal velocity in greyhounds to 100.3 in humans. Further analysis based on a subset of individuals and using an 'animal model' shows that running spe...
Autologous point-of-care cellular therapies variably induce equine mesenchymal stem cell migration, proliferation and cytokine expression. Autologous cellular therapy products including adipose-derived stromal vascular fraction (SVF), bone marrow mononuclear cells (BMMNs), cord blood mononuclear cells (CBMNs) and platelet rich plasma are options for treatment of acute orthopaedic lesions while mesenchymal stem cells (MSCs) are culture expanded. These products may contribute to healing by secreting matrix proteins or growth factors, but they may also act on endogenous MSCs to facilitate healing. Objective: To determine the effects of cell therapy products on MSCs function in vitro. The hypothesis was that cell therapy products pro...
Periodontal biomechanics: finite element simulations of closing stroke and power stroke in equine cheek teeth. In equine dentistry periodontal diseases, especially periapical inflammation, are frequently occurring problems. Anachoresis is believed to be the most common cause for the development of such disorders. Nevertheless, there is still no substantiated explanation why settlement of pathogen microorganisms occurs in equine periodontal tissues. It is expected that excessive strains and stresses occurring in the periodontal ligament (PDL) during the horse's chewing cycle might be a predisposing factor. In this study this assumption was examined by finite element (FE) analyses on virtual 3-D models o...
