Veterinary medicine for horses encompasses the study and application of medical practices to diagnose, treat, and prevent diseases in equine species. This field involves a comprehensive understanding of equine anatomy, physiology, pathology, and pharmacology. Veterinary practitioners employ a range of diagnostic tools and therapeutic interventions to address health issues in horses, including lameness, gastrointestinal disorders, respiratory conditions, and infectious diseases. Preventative care, such as vaccination and deworming programs, is also a significant aspect of equine veterinary medicine. This page gathers peer-reviewed research studies and scholarly articles that explore various aspects of veterinary medicine as it pertains to horses, including advancements in diagnostic techniques, treatment protocols, and preventive health strategies.
Card CE, Manning ST, Bowman P, Leibel T.Breeding or semen collection was attempted using: natural cover, manual stimulation, artificial vagina, pharmacologic induction of ejaculation, and electroejaculation. Sperm cells were recovered from the ductus deferens and epididymides post mortem. Only semen collected ex copula by imipramine and xylazine treatment resulted in conceptions (4/5). This is the first report of pregnancies in horses from ex copula semen collection.
Breit S.Ten horses, younger than 1 year, were used to investigate the articulatio interphalangea distalis of the pelvic limb. The expansion of the dorsal recess was compared to those of adult horses. The recessus dorsalis always formed a shape like the letter 'm' or like a triangle with oblique angles. Consequently the great proximo-distal expansion on the medial side of the dorsal recess very probably has nothing to do with the age of horses.
Chu JW, Sharom FJ, Oriol JG, Betteridge KJ, Cleaver BD, Sharp DC.The equine embryonic capsule, an acellular covering that envelops the conceptus during the second and third weeks of pregnancy, is composed of mucin-like glycoproteins. Its structure is consistent with a dual role during early pregnancy: protection of the conceptus, and communication between the embryo and the mother. Loss of sialic acid from the capsular glycoproteins at day 16 correlates with the time of "fixation," or loss of conceptus mobility throughout the uterine horns. This study investigated how the structure of the capsule is linked to the maintenance of pregnancy. Six pregnancies, c...
Rees WA, Harkins JD, Woods WE, Blouin RA, Lu M, Fenger C, Holland RE, Chambers TM, Tobin T.Amantadine is an antiviral agent effective against influenza A viruses. We investigated 1) the antiviral efficacy, 2) analytical detection, 3) bioavailability and disposition, 4) pharmacokinetic modelling and 5) adverse reactions of amantadine in the horse. In vitro, amantadine and its derivative rimantadine suppressed the replication of recent isolates of equine-2 influenza virus with effective doses (EDs) of less than 30 ng/ml. Rimantadine was more effective than amantadine against most viral isolates; we suggest a minimum plasma concentration of 300 ng/ml of amantadine for therapeutic effic...
Flaherty D, Reid J, Welsh E, Monteiro AM, Lerche P, Nolan A.The pharmacodynamics of infusions of propofol alone (group 1) were compared with the pharmacodynamics of infusions of propofol and ketamine together (group 2) in eight ponies undergoing castration. Anaesthesia was induced with detomidine, 20 micrograms kg-1, followed by ketamine, 2.2 mg kg-1. Subsequently, a bolus dose of propofol, 0.5 mg kg-1, was administered intravenously to both groups, and an infusion of propofol was given for an average of 74 minutes to group 1, and an infusion of propofol and ketamine was given for 60 minutes to group 2. The mean (SD) infusion rates of propofol were 0.3...
Hamm D, Turchi P, Johnson JC, Lockwood PW, Thompson KC, Katz T.To titrate a clinically effective eltenac dosage (0.1, 0.5, and 1.0 mg/kg of body weight), compared with vehicle only, and to compare efficacy of the most effective eltenac dosage with that of 1.1 mg of flunixin meglumine/kg. Methods: 40 healthy horses, ranked after model induction on the basis of lameness severity, were randomly assigned to 5 treatment groups, with 4 replicates of 10 horses each. Methods: On day -5, after surgical preparation of the left carpal region, 0.7 ml of Freund's complete adjuvant was injected into the intercarpal space. Horses were observed daily, from the day of car...
Patterson-Kane JC, Wilson AM, Firth EC, Parry DA, Goodship AE.This study was undertaken to test the hypothesis that collagen fibrils, the submicroscopic units of strength in tendon, would hypertrophy in response to a specific defined training programme. Fibril diameters were measured in central and peripheral regions of superficial digital flexor tendon (SDFT) samples from five 18-month-old horses which underwent a subsequent 18 month training programme and 6 age- and sex-matched controls. Central region fibrils from the trained horses had a mass-average diameter (MAD) of 105.3 nm, which was significantly lower (P < 0.01) than that of 131.7 nm for the...
Basher AW, Severin GA, Chavkin MJ, Frank AA.Three horses were examined because of exophthalmos and others signs indicative of a space-occupying orbital mass. In 2 horses, exenteration was used to remove the orbital mass. In a third horse, an orbital tumor and lung metastases were found at necropsy. Routine histologic and Grimelius' histochemical staining were used on fixed tissues; immunohistochemical staining for chromogranin and electron microscopy also were performed. Masses were orbital neuroendocrine tumors. Horses that underwent exenteration were alive 19 and 24 months after surgery. Hypotension was encountered at surgery in both ...
Klonisch T, Mathias S, Cambridge G, Hombach-Klonisch S, Ryan PL, Allen WR.In situ hybridization employing a cRNA probe derived from a 428-bp fragment of equine relaxin was used to localize relaxin mRNA, and immunocytochemistry was used to localize relaxin itself, in tissues of the placenta-endometrium interface recovered between 33 and 153 days of gestation from mares carrying intraspecific horse, interspecific mule and extraspecific donkey conceptuses. Immunocytochemical staining was also used to localize trophoblast-specific and class I major histocompatibility complex (MHC) antigens on some specimens. Relaxin mRNA and relaxin were both present in the single-cell ...
Pleasant RS, Moll HD, Ley WB, Lessard P, Warnick LD.To determine if intra-articular anesthesia of the distal interphalangeal joint could alleviate lameness associated with the navicular bursa in horses. Methods: Experimental investigation. Methods: Six clinically normal horses. Methods: Lameness was induced in each horse by injecting either the left or right front navicular bursa with 5 mg of amphotericin-B. Forty-eight hours later each horse was videotaped walking and trotting before, and 5, 30, and 60 minutes after injecting the distal interphalangeal joint of the treated limb with 5 mL of 2% mepivacaine hydrochloride. All video recordings we...
McD○ LA, Stover SM, Taylor KT.To determine the monotonic mechanical properties of osteotomized adult equine tibiae stabilized with two dynamic compression plates (DCP) and to compare the mechanical properties with those of intact tibiae and in vivo loads. Methods: The compressive, bending, and torsional mechanical properties of plated and intact tibiae were assessed in vitro. Methods: Twelve pairs of adult equine tibiae. Methods: Tibiae were loaded in axial compression, craniocaudal 3-point bending, or torsion in external rotation in a single cycle to failure. Mechanical properties were determined from load-displacement da...
Birch HL, Rutter GA, Goodship AE.Hypoxia has been suggested as a possible cause of tissue degeneration and subsequent rupture in equine tendons. To determine whether low oxygen tension is likely to be detrimental to tendon cell function, experiments were designed to investigate oxidative energy metabolism in freshly isolated and cultured equine tendon cells. Freshly isolated tenocytes and cultured fibroblasts possessed activities of the mitochondrial enzyme citrate synthase similar to those of other mammalian cells, with well defined oxidative metabolism. D-[6(-14)C]-glucose oxidation was measurable in both freshly isolated a...
Barlough JE, Rikihisa Y, Madigan JE.A nested polymerase chain reaction was developed for amplifying a 529-bp segment of the 16S ribosomal RNA gene of Ehrlichia risticii from equine buffy coat cells. Confirmation of identity of the amplified bands was accomplished by Southern hybridization and DNA sequencing. The study indicated a detection limit of > 10 copies of the target gene, and specificity for E. risticii as based on a panel of test rickettsiae. Ticks (Ixodes pacificus) collected in an area of northern California enzootic for equine monocytic ehrlichiosis were found to be negative for E. risticii DNA.
Sysel AM, Pleasant RS, Jacobson JD, Moll HD, Warnick LD, Sponenberg DP, Eyre P.The purpose of this study was to determine the systemic and local effects associated with long-term epidural catheterization and epidural morphine-detomidine administration in horses. Methods: Development of systemic or local effects was assessed by placing caudal epidural catheters in study horses and administering injections through the catheters every 12 hours for 14 days. Methods: Ten horses with epidural catheters that received daily injections; six uncatheterized horses presented for euthanasia. Methods: Horses received either 0.2 mg/kg morphine sulfate and 30 micrograms/kg detomidine hy...
Moore BR, Krakowka S, Mcvey DS, Cummins JM, Robertson JT.Protein and eicosanoid concentrations and procoagulant activity were determined in bronchoalveolar lavage fluid (BALF) from 32 Standardbred racehorses with inflammatory airway disease (IAD) and 6 control horses. Total protein, albumin and immunoglobulin G (IgG) concentrations were high (P < 0.05) in the BALF from horses with IAD, a finding consistent with exudation of plasma protein into the airway. Immunoglobulin A (IgA) concentrations also were increased (P < 0.05) which may signify local immunoglobulin production. Difference was not detected in prostaglandin E2 and 6-ketoprostaglandin...
Simonsen U, Prieto D, Hernández M, Sáenz de Tejada I, García-Sacristán A.The receptors mediating the contractions to both exogenously applied noradrenaline and electrical field stimulation (EFS) were characterized in horse isolated penile resistance arteries. The alpha 1-adrenoceptor-selective antagonist, prazosin, caused competitive rightward shifts of the contractile concentration-response curves (CRC) to phenylephrine. The alpha 2-antagonist, rauwolscine, also displaced to the right the CRC to the alpha 2-adrenoceptor-selective agonist, BHT 920. EFS (0.3 ms, 20-second trains) caused tetrodotoxin-sensitive frequency-dependent contractions which were enhanced in t...
Yamaya Y, Kubo K, Amada A, Sato K.The atrioventricular (AV) conductive functions were investigated before and after the pharmacological autonomic nervous blockade (PAB) through the electrophysiological study on six horses (AV block group) in which the dropped beats occurred more frequently (over 200 beats/24 hr) and on five horses (control group) in which the dropped beats occurred sporadically (under 200 beats/24 hr) or in which the arrhythmias were not recognized at all on the long-term electrocardiogram. As a result, AV conductivity, conduction time and refractoriness in the AV block group were lower, longer and higher, res...
Paweska JT.Eight sexually mature horse stallions were inoculated intranasally with a South African asinine strain of EAV, a strain that was isolated from the semen of a donkey carrier. All horses developed fever, with maximum rectal temperatures of 38.9-39.9 degrees C recorded 3-6 d post challenge. Six horses showed very mild clinical signs of equine viral arteritis and two were asymptomatic. The virus was recovered from the nasopharynxes of six horses 2-7 d after inoculation, and from buffy-coat samples of all horses, 2-11 d after inoculation. Seroconversion to EAV was detected on days 8 and 10 and peak...
Johnson CB, Taylor PM.Opioids have variable effects on the minimum alveolar concentration of inhaled anaesthetics in the horse. During halothane anaesthesia at an end-tidal halothane concentration between 0.75 and 0.85 percent, the electroencephalogram (EEG) frequency power spectrum and the auditory evoked potential were recorded continuously in eight ponies during an infusion of approximately 40 micrograms kg-1 alfentanil over five minutes, and for a further 55 minutes. The spectral edge and median frequency of the EEG and the mid-latency of the auditory evoked potential at the time of maximum change of these vari...
Malinowski K, Christensen RA, Konopka A, Scanes CG, Hafs HD.Sixteen 20- to 26-yr-old mares were given 0, 6.25, or 12.5 mg/d equine somatotropin (eST) to determine whether aged mares respond to ST with changes in feed intake, body weight, body condition score (based mostly on fat cover), or immunocompetence. Neither dry matter intake, body weight, nor body condition scores were altered during the 6 wk of eST injection. However, based on photographs taken to evaluate musculation before and after treatment (scores 0 to 4), mares given eST developed greater (P < .07) muscle definition (1.8 +/- .6 and 2.5 +/- .6 for 6.25 and 12.5 mg eST/d, respectively) ...
Raekallio M, Taylor PM, Bennett RC.Twenty-five horses undergoing arthroscopic surgery were studied to develop a scheme for assessing pain in horses while investigating the effects of phenylbutazone (PBZ) analgesia. Fifteen of the 25 horses received PBZ 4 mg/kg intravenously (IV) before surgery and 2 mg/kg (IV) every 12 hours thereafter until 60 hours; the remaining 10 (placebo group) were given a corresponding volume of saline. In both groups, venous blood samples were collected for catecholamine, beta-endorphin, and cortisol assays before premedication and up to 72 hours after surgery. Postoperative pain was evaluated by measu...
Saville WJ, Reed SM, Granstrom DE, Hinchcliff KW, Kohn CW, Wittum TE, Stamper S.To determine the seroprevalence of serum antibodies to Sarcocystis neurona in horses residing in Ohio. Methods: Prevalence survey. Methods: Serum from samples from 1,056 horses. Serum was collected on every 36th sample submitted to the Ohio State Diagnostic Laboratory for testing for equine infectious anemia. Methods: Serum was frozen at -80 C and analyzed for antibodies to S neurona, using a western blot. Information regarding blood sample collection, age, breed, sex, and geographic location was recorded for each horse. Data were analyzed, using multivariable logistic regression. Results: Hor...
Blythe LL, Granstrom DE, Hansen DE, Walker LL, Bartlett J, Stamper S.To determine seroprevalence of antibodies to Sarcocystis neurona in neurologically normal horses residing in 4 regions of Oregon and to describe the effects of age, gender, breed, and housing on seroprevalence within each region. Methods: Prevalence survey. Methods: Serum samples from 334 horses systematically selected by practicing veterinarians. Methods: Antibodies to S neurona were measured in sera, using a western blot. Information including age, gender, breed, housing, geographic location, and duration of residence was obtained for each horse. Data were analyzed, using descriptive statist...
Peters JW.The most feared complication after a rectal examination of horses and ponies is to cause a tear of all the layers in the intraperitoneal part of the rectum. The description of the anatomy is an attempt to explain that the rectal tear is mostly located in the dorsal or dorsolateral part of the rectum. This article describes a relatively simple suture technique for the rectal tear by using the needle of Deschamp which is modified by Professor B. Huskamp. Furthermore there is a description of this method as treatment of two horses in practice circumstances. The issue whether causing a rectal tear...
Archer DC, Clegg PD, Edwards GB.A 21-year-old Arab gelding with clinical signs of acute peritonitis had a perforating ulcer on the mesenteric border of the jejunum which resulted in localised contamination of the abdomen with ingesta. The affected segment of jejunum was resected and the abdomen was lavaged extensively. Postoperatively, the gelding was treated with broad-spectrum antibiotics, non-steroidal anti-inflammatory drugs and intravenous fluids, but after four days it became acutely non-weight bearing on its right hindlimb, and a tendonitis of the lateral digital flexor tendon within the tarsal sheath was identified u...
Pascoe JR, Ellenburg TV, Culbertson MR, Meagher DM.A 360-degree torsion of the left spermatic cord was diagnosed in a 2 1/2-year-old Quarter Horse colt. Clinical signs included abdominal discomfort, with slight elevations in heart and respiratory rates. The scrotum on the left side was moist and edematous. The left testicle was enlarged, firm, and retracted slightly toward the abdominal cavity. The colt resented palpation of the testicle. On rectal palpation, the left vaginal ring and the structures passing through the ring were edematous and painful to pressure. Surgical correction was achieved by emasculation. The tail of the epididymis and ...
Timms M, Ganio K, Forbes G, Bailey S, Steel R.CJC-1295 is a 30 amino acid peptide-based drug that stimulates the release of growth hormone (GH) from the pituitary gland. It is unique among performance-enhancing peptides due to the presence of a reactive maleimidopropionic acid group that covalently links the peptide to free thiols on the surface of plasma proteins. Once conjugated, CJC-1295 remains active in the bloodstream for significantly longer than non-conjugated peptide-based drugs that are rapidly excreted. Conjugation of CJC-1295 to plasma proteins prevents its detection by top-down mass-spectrometry-based peptide screening protoc...
Allen K, Anderson L, King M, Mullan S.The ethics of using horses in sport is receiving increasing attention and media scrutiny. Sports medicine ethics is an important and well-established discipline within human medicine and biomedical ethics, which has, thus far, received little application to the equine veterinary field. Objective: The purpose of this scoping review was to explore the existing literature on equine sports medicine ethics, to understand the current concerns and issues, and to map areas for future research. Methods: Scoping review. Methods: Academic databases (PubMed, Web of Science, CAB abstracts) were searched to...
Behnke R.Hoof-ground interaction impacts on the health and performance characteristics of horses. Due to complex interactions between hoof and ground during the stance phase, previous experimentally dominated studies concentrated on subproblems of the phenomena observed. A multidisciplinary methodology with mathematical modelling, material testing and in vivo experimental measurements seems promising. Objective: With the help of a mathematical approach, this contribution aims to explain from a biomechanical point of view the phenomena observed during experimental investigations (hoof acceleration, inte...
Siedek EM, Whelan M, Edington N, Hamblin A.Equine herpesvirus type 1 (EHV-1) causes respiratory disease, abortion and myeloencephalopathy in horses. As with other herpesviruses, cell-mediated immunity is considered important for both recovery and protection. Although virus-specific T-cell proliferation and cytotoxicity can be detected following in vivo infection, little is known about the role of antigen presenting cells such as dendritic cells (DCs) in these processes. Peripheral blood DCs were shown to express the viral glycoprotein gB perinuclearly following exposure to EHV-1 in vitro, demonstrating EHV-1 replication within them. Co...
Orsini JA, Nunamaker DN.A 4-year-old Standardbred stallion sustained a severely comminuted fracture involving the second, third, and fourth metacarpal bones. The fracture was repaired using two 14-hole broad dynamic compression plates positioned at 90 degrees to one another, allowing one plate to protect the other in the bending mode. An autologous cancellous bone graft obtained from the tuber coxae was added at the site of the defect in the mid- to upper third of the third metacarpal bone. Complications associated with the fixation included a Staphylococcus aureus infection 5 months after surgery, laminitis that dev...
Shearer TR, Kinsley MA, Pease AP, Patterson JS.The purpose of this study was to develop a minimally invasive approach to equine cervical articular facet joints for application of an ND:YAG LASER and to evaluate the effects of the laser fiber on the surrounding tissue. Under general anesthesia, an ND:YAG LASER was used to apply 2000 J of energy to 5 cervical articular facet joints in 3 horses (15 joints total). Horses were euthanized and the cervical facets and spinal cords were examined grossly and histologically. Gross pathology of the articular facets revealed evidence of articular cartilage charring and diffuse roughening of the surface...
Bell RJ, Textor JA.To establish the prevalence of intussusceptions involving the caecum in a population of horses admitted to a university hospital for colic. Methods: Retrospective clinical study Methods: Medical records of all horses admitted to the Massey University Veterinary Teaching Hospital between 1991 and 2004 were examined for information of those horses diagnosed with an intussusception involving the caecum. Results: A total of 135 horses were admitted for colic surgery during the study period and 61 horses had a diagnosis of ileocaecal (37), caecocaecal (5) or caecocolic intussusception (19) made eit...
Goodrich LR, Moll HD, Crisman MV, Lessard P, Bigbie RB.To evaluate healing of pinch-grafted wounds on the distal aspect of the limbs of ponies bandaged with equine amnion or a standard nonadherent wound dressing material. Methods: 6 ponies. Methods: A 2.5x2.5-cm full-thickness section of skin was removed from the dorsal aspect of each limb at the midpoint of the metacarpus or metatarsus. Six days later, wounds were grafted with partial-thickness pinch grafts. Half the wounds were bandaged with amnion, and the other half were bandaged with a nonadherent dressing. Bandages were changed every 3 days until wound healing was complete. At each bandage c...
Holterman WF, de Voogt P, Peereboom-Stegeman JH.Cadmium and zinc were determined in kidney cortex of 63 horses and 51 red deer (Cervus elaphus). Cadmium and zinc were also determined in protein fractions obtained by Sephadex chromatography of kidney cortex from 10 horses and 4 red deer. Histopathological parameters in kidney cortex of horses were compared to cadmium content. The metal contents (on wet weight basis) in kidney cortex of the horses were 0.31 +/- 0.22 mmole Cd/kg (range 0.03-1.21) and 0.63 +/- 0.17 mmole Zn/kg (range 0.36-1.23). The Zn content increased with the Cd content, the Zn increase being less at higher concentrations. N...
Hough ME, Steel CM, Bolton JR, Yovich JV.Four cases of ulceration and stricture of the right dorsal colon were encountered. Ulceration of the right dorsal colon is generally associated with nonsteroidal anti-inflammatory drug (NSAID) toxicosis but there are few reports of stricture following ulceration. All four horses had recent phenylbutazone use: three had been given doses well in excess of the recommended dose and in one the dose was marginally above those recommended but was combined with administration of other NSAIDs. All four horses presented with intermittent low-grade colic, weight loss and ventral oedema. Diarrhoea was als...
Obi TU, Taylor WP.Serum samples collected from 1,197 goats, 586 sheep, 254, cattle, 55 dogs and 44 horses were examined for antibodies to adenovirus by the agar-gel precipitation test. Results show that 17.7% of the goats, 18.4% of the sheep, 4.3% of the cattle, and 4.5% of the horses had precipitating antibodies. None of the dog sera examined was positive. The results seem to indicate a moderate level of previous exposure to adenovirus infection especially among goats and sheep in Nigeria.
McManus CJ, Davison LA, Fitzgerald BP.In a variety of species, glucoprivation results in the suppression of the reproductive axis. Two experiments were performed to test the hypothesis that blockade of glucose metabolism via administration of the glucose inhibitor 2-deoxy-D-glucose (2DG) to mares would cause a modification in gonadotropin and prolactin secretion. Long-term ovariectomized mares (Experiment 1, n=4) or ovary-intact mares during the follicular phase of a synchronized estrous cycle (Experiment 2, n=4 per dose) were treated with 2DG. The dose of 2DG used in Experiment 1 was 100mg 2DG/kg BW, but because severe behavioral...
Frerichs WM.The effect of imidocarb dipropionate [3, 3' bis-(2-imidazolin-2-yl) carbanilide dipropionate] on spermatogenesis in 3 pony stallions was studied. The drug alone had no deleterious effect on spermatogenesis when given intramuscularly 4 times at a dosage level of 4 mg/kg at 72-hour intervals. Hemicastration, with or without subsequent drug treatment, caused almost complete cessation of spermatogenesis 30 days after the operation.
Gasthuys F, Pockelé K, Vervaet C, Weyenberg W, De Prijck K, Pille F, Vlaminck L, Nelis H, Remon JP.The in vivo behaviour of 5% gentamicin sulphate ocular mini-tablets (2-mm diameter, 6.525 mg weight) was compared with gentamicin eye drops in six ponies. Two mini-tablets were inserted on the bulbar conjunctiva of the right eye while a similar dose of gentamicin was administered via eye drops in the left eye. Irritation induced by the mini-tablets and the eye drops was evaluated using a visual analogue scale (0-10). Tears were sampled with ophthalmologic absorption triangles for 1 min for the determination of the concentration of gentamicin sulphate using a microbiological plate diffusion met...
Perillo A, Passantino G, Passantino L, Cianciotta A, Mastrosimini AM, Lacovazzi P, Venezia P, Jirillo E, Troncone A.Among 622 slaughtered horses from eastern Europe, 156 thyroid glands were selected on the basis of macroscopic alterations (e.g., determination of volume and weight). In the 80% of these thyroids, microscopic alterations consistent with a diagnosis of Hashimoto thyroiditis-like disease were found. In particular, a subverted architecture of the thyroid gland with colloid rarefaction, lymphocytic infiltration, and fibrosis was noted. The confirmation of the histopathological diagnosis of an equine Hashimoto thyroiditis-like disease was provided by the increased serum concentration of thyroglobul...
Gilliam LL, Ownby CL, McFarlane D, Canida A, Holbrook TC, Payton ME, Krehbiel CR.Rattlesnake bites in horses are not uncommon and the clinical outcomes are widely variable. Treatment of horses with anti-venom is often cost prohibitive and could have negative consequences; therefore, the development of a quantitative test to determine if anti-venom therapy is indicated would be valuable. The objective of this study was to develop an ELISA to detect rattlesnake venom in biological samples from clinically bitten horses. Nineteen horses were enrolled in the study. Urine was available from 19 horses and bite site samples were available from 9 horses. A double sandwich fluoresce...
Hellyer PW, Bednarski RM, Hubbell JA, Muir WW.Baroreflex sensitivity (BS) was used to quantitatively assess the effects of halothane and isoflurane on the heart rate/arterial pressure relationship during steady-state (10 minutes) and dynamic pressure changes in adult horses. Arterial pressure was decreased in response to nitroglycerin or sodium nitroprusside and increased in response to phenylephrine HCl. Mean (+/- SEM) BS in awake horses was 28.9 +/- 2.6 and 13.2 +/- 2.0 ms/mm of Hg during steady-state decreases and increases in systolic arterial pressure (SAP), respectively. Halothane and isoflurane either significantly (P less than 0.0...