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Topic:Respiratory Health
Respiratory health in horses encompasses the study of the equine respiratory system, its function, and the various conditions that can affect it. The respiratory system in horses includes the upper airways, lungs, and associated structures, which facilitate gas exchange and are vital for maintaining physiological homeostasis during rest and exercise. Common respiratory conditions in horses include equine asthma, infectious diseases like strangles, and exercise-induced pulmonary hemorrhage (EIPH). These conditions can impact a horse's performance and overall health. This page compiles peer-reviewed research studies and scholarly articles that explore the anatomy, physiology, pathophysiology, and management of respiratory health in horses.
Ventilatory support of the neonatal foal. Many sick neonatal foals have respiratory failure secondary to perinatal hypoxia, sepsis, or pneumonia. These foals require ventilatory support to prevent respiratory embarrassment and other complications associated with chronic hypoxia and hypercapnia. This article discusses practical aspects of ventilatory therapy, such as choosing a candidate for mechanical ventilation, choosing the proper ventilatory mode, placing a foal on a ventilator, maintaining a foal on mechanical ventilation, and weaning from mechanical ventilation. This article details some of the techniques that have been develope...
Peripartum asphyxia. The abysmal survival rates for the first barking foals described more than 60 years ago were probably due to the cumulative effects of asphyxia on multiple organ systems. Successful treatment of asphyxiated foals requires recognition of periparturient conditions associated with the syndrome and appreciation of the spectrum of clinicopathologic complications that can ensue.
Pneumocystis carinii pneumonia in foals. Pneumocystis carinii pneumonia was diagnosed in 3 foals. In 2 foals (No. 1 and 2), diagnosis was by histologic evaluation of pulmonary tissue. On retrospective evaluation, P carinii cysts were found on sediment smears of bronchoalveolar lavage fluid in 1 foal (No. 1). A different foal (No. 3) was diagnosed as having pneumocytosis by finding P carinii cysts in bronchoalveolar lavage fluid, and was treated successfully. Definitive diagnosis of pneumocytosis in animals is usually made at necropsy. However, careful cytologic evaluation in bronchoalveolar lavage fluid sediment can provide a diagnos...
Neonatal development of the diaphragm of the horse, Equus caballus. The diaphragm of neonatal horses is significantly different from the diaphragm of adult horses in terms of histochemical fiber type composition, myosin heavy chain isoform, and native myosin isoform composition. There is a significant increase in the percentage of type I fibers present in the diaphragm with increasing age from birth through about seven months postnatal age. A possible lack of postural tone in the hiatal region of the neonatal diaphragm is suggested to account for increased incidence of vomiting or aspiration pneumonia in younger horses. The isoform data lead to rejection of th...
The prevalence of latent Equid herpesviruses in the tissues of 40 abattoir horses. Equid herpesviruses 1 or 4 (EHV-1 or -4) were isolated by cocultivation from 60% of 40 horses examined at slaughter. The lymph nodes draining the respiratory tract were the most common source of virus. EHV-1 or EHV-4 was never isolated from the trigeminal ganglia (SLG). The polymerase chain reaction (PCR) detected virus in 87.5% of bronchial lymph nodes and a similar level in the trigeminal ganglia that were examined. By both assays approximately one third of the positive animals harboured both viruses. Equid herpesvirus 2 (EHV-2) was isolated from all but one of the horses and from > 75% o...
The rapid and effective administration of a beta 2-agonist to horses with heaves using a compact inhalation device and metered-dose inhalers. The purpose of the study was to administer therapeutic aerosol generated by metered-dose inhalers to horses exhibiting clinical signs of heaves using a compact inhalation device developed for human medicine. It was fitted to a custom face mask in order to study the effect of an inhaled beta 2-agonist, fenoterol. Pulmonary function testing was performed on six horses following an acute exacerbation of heaves, characterized by tachypnea, wheezes, crackles, and spasmodic cough. Horses inhaled fenoterol in 1 mg increments administered as one 200 microgram puff every 5-10 s with the recording of da...
Cutaneous hemangiosarcoma with pulmonary metastasis in a horse. A 6-year-old Thoroughbred mare had a 7-cm ulcerated mass on the cranial aspect of the left cervical area. Ultrasonography revealed the mass to be < 1 cm thick and composed of small lobules that were filled by material hypoechoic to the surrounding muscle tissues. Fine-needle aspiration of the mass yielded blood, and cytologic examination revealed a few epithelial cells with neoplastic changes. Thoracic radiography revealed an interstitial pattern with several disseminated nodules. A diagnosis of cutaneous hemangiosarcoma with pulmonary metastases was made. The diagnosis was confirmed at nec...
Repeatability and normal values for measurement of pharyngeal and tracheal pressures in exercising horses. Repeatability of measurements of peak and mean tracheal and pharyngeal pressures in exercising horses was determined. Five athletically fit horses were subjected to repeated (n = 5) standardized exercise trials. Static pressures in the trachea, nasopharynx, and mask were determined. At least 96% of all mean pressure measurements were within 5 cm of H2O of the mean value for any horse. Peak pressure measurements were less repeatable, but at least 96% of all measurements were within 10 cm of H2O of the mean peak measurements for any horse. In 10 horses galloping at 14 m/s, the 95% confidence int...
Evaluation of partial arytenoidectomy as a treatment for equine laryngeal hemiplegia. The efficacy of partial arytenoidectomy was assessed in 6 Standardbred horses, with surgically induced laryngeal hemiplegia, at rest (Period A) and during exercise at speeds corresponding to maximum heart rate (Period C) and 75% of maximum heart rate (Period B). Peak expiratory and inspiratory airflow rate (PEF and PIF), and expiratory and inspiratory transupper airway pressure (PUE and PUI) were measured and expiratory and inspiratory impedance (ZE and ZI) were calculated. Simultaneously, tidal breathing flow-volume loops (TBFVL) were acquired using a respiratory function computer. Indices de...
Diaphragm and lung afferents contribute to inspiratory load compensation in awake ponies. We determined the effect of pulmonary vagal (hilar nerve) denervation (HND) and diaphragm deafferentation (DD) on inspiratory load compensation. We studied awake intact (I; n = 10), DD (n = 5), HND (n = 4), and DD+HND (n = 7) ponies at rest and during mild (1.8 mph, 5% grade) and moderate (1.8 mph, 15% grade) treadmill exercise before, during, and after resistance of the inspiratory circuit was increased from approximately 1.5 to approximately 20 cmH2O.l-1.s. During the first loaded breath in I ponies at rest, inspiratory time (TI) increased, expiratory time decreased, and inspiratory drive in...
The role of the carotid chemoreceptors in the control of breathing during exercise. Our objective was to gain insight into the role of the carotid chemoreceptors (CC) in the exercise hyperpnea. Humans and ponies were studied at rest and during submaximal exercise breathing room air. In healthy humans, alveolar ventilation (VA) was tightly matched to CO2 production (CO2) resulting in PaCO2 deviating during exercise less than 1-2 mm Hg from rest. In contrast, ponies' VA increased proportionately more than VCO2 during exercise resulting in a workload dependent hypocapnia. Attenuating CC activity through hyperoxia had no effect on exercise PaCO2 of humans but hyperoxia accentuate...
[The oxygen pathway: how well-built is the respiratory system?]. The question is explored of how the structural systems that constitute the pathway for oxygen from the air through the lung and the circulation of blood to the mitochondria in muscle cells affect the O2 flow rate, and whether their quantitative structural characteristics conform to the hypothesis of symmorphosis which postulates a match of structural design to overall functional demand. By combining physiological and morphometric studies, it is first demonstrated that the diffusing capacity of the human lung is slightly larger than that needed for maximal O2 uptake. Comparative studies of smal...
Characterization, distribution, and microbiological associations of Fusobacterium spp. in clinical specimens of animal origin. During the years from 1984 through 1991, 1,067 specimens from canine, equine, exotic, feline, porcine, and ruminant animal sources were found to contain members of the genus Fusobacterium: The most common sites or conditions from which members of this genus were isolated were abscesses, the respiratory tract, and pleural and peritoneal cavities. Most specimens contained a single Fusobacterium species. The most commonly isolated species was Fusobacterium necrophorum. Almost all of the specimens contained other obligate anaerobes together with facultative and obligate aerobes. The identities of ...
Cardiovascular effects of intermittent positive pressure ventilation in the anesthetized horse. Intermittent positive pressure ventilation (IPPV) is useful method for compensate of respiratory function in anesthetized horses. However, IPPV may decrease cardiac output. Alterations in cardiac output of three groups (N = 5) healthy, halothane-anesthetized mares were determined and compared during a 120 min period of anesthesia. The groups were as follows: spontaneous ventilation (SV), controlled ventilation using an end-inspiratory pressure of 20 cmH2O (CV20) and a third group using 25 cmH2O (CV25) inspiratory pressure. In the CV groups, respiratory function was adequately maintained. Altho...
Mechanisms of exercise-induced pulmonary hemorrhage in the equine athlete. This article discusses exercise-induced pulmonary hemorrhage (EIPH), a pathophysiological syndrome which occurs worldwide in the equine athlete. It reviews the history of EIPH, the incidence in performance horses, the etiology, studies performed on the treadmill to determine the mechanisms of EIPH, and the most likely causes of stress failure of the pulmonary capillaries.
Respiratory mechanics of the horse during the first year of life. This study investigated the developmental changes in the mechanical properties of the respiratory system in growing horses. Pulmonary mechanics and lung volumes were serially measured in anesthetized foals during the first year of life. Quasi-static pressure-volume curves were generated, and functional residual capacity (FRC) was measured using a closed nitrogen equilibration technique. At birth, chest wall compliance normalized to body weight was substantially less than that reported in other less precocious newborn species, while lung compliance normalized to body weight was similar to value...
Pneumocystis carinii pneumonia in thoroughbred foals: identification of a genetically distinct organism by DNA amplification. Genetically distinct forms of Pneumocystis carinii infect several mammalian hosts. We report the amplification of P. carinii DNA from samples of two infected thoroughbred foal lungs by using primers designed from the sequence of a P. carinii mitochondrial rRNA gene; these primers also prime the amplification of P. carinii DNA from other hosts. The nucleotide sequence of part of the mitochondrial rRNA gene amplified from P. carinii infecting one of the foals was determined and found to be distinct from that of published rat-, rabbit-, ferret-, and human-derived P. carinii sequences.
Inhibitory nerve distribution and mediation of NANC relaxation by nitric oxide in horse airways. The distribution of inhibitory nerves and the mediator of the inhibitory nonadrenergic noncholinergic (iN-ANC) nervous system were investigated in smooth muscle preparations from seven regions of equine airways. In tissues incubated with atropine and precontracted with histamine, electrical field stimulation produced frequency-dependent relaxation, and the magnitude of the relaxation decreased from trachea to central bronchi and was absent in peripheral airways. The degree of relaxation in bronchi was not simply a function of bronchial size or generation. Propranolol inhibited part of the rela...
Influence of air movement, facemask design and exercise on upper airway, transpulmonary, and transdiaphragmatic pressures in thoroughbred horses. The influences of facial airflow, exercise and wearing a facemask on gas exchange and upper airway (Pu), transpulmonary (PTP) and transdiaphragmatic (PTD) pressures were investigated in 6 horses performing an incremental exercise test on an inclined (10%) treadmill. The test consisted of a 2 min walk followed by two 2 min exercise bouts at intensities which produced 40% and 80% of maximal oxygen consumption. Horses performed the test 4 times, once for each of 4 protocols, which involved not wearing a facemask (A), wearing a mask with either no biased flow through it (B), with an expiratory bia...
[Air sac mycosis: topical treatment using enilconazole administered via indwelling catheter]. In a horse with chronic unilateral nasal discharge guttural pouch mycosis caused by Aspergillus fumigatus was diagnosed. A percutaneous indwelling catheter was surgically installed in the left guttural pouch. Initial treatment with a povidone iodine solution proved to be unsatisfactory. Treatment was continued by administering enilconazole by ways of an indwelling through-the-nose-catheter. The latter treatment resulted in complete recovery.
Susceptibility of ponies to infection with Streptococcus pneumoniae (capsular type 3). Welsh Mountain ponies were inoculated with an isolate of Streptococcus pneumoniae, SPE 1618 (capsular type 3) recovered from the equine respiratory tract: 10 ml of a suspension of 10(8) or 10(9) cfu/ml were instilled intratracheally. Fever was observed after either dose but the greater concentration also produced coughing, ocular and nasal discharge, depression and enlargement of submandibular lymph nodes. Cytological evidence of infection was also observed in tracheal washings during the first week after inoculation and corresponded with isolation of S. pneumoniae from the washes. Morbid anat...
Cardio-respiratory, haematological and biochemical parameter adjustments to exercise: effect of a probiotic in horses during training. Two randomly distributed groups of thoroughbred horses were compared during a 12-week period for their cardio-respiratory and metabolic adjustment to strenuous exercise, training and detraining. The horses were trained following the same standardized schedule and were regularly investigated using standardized treadmill exercise tests (SET) of increasing speed. After the first SET and during the whole experimental period, a group of 6 horses received a probiotic (Bioracing) once a day while a group of 5 horses received a placebo. All other conditions were similar for both groups. During each SE...
Drugs affecting the hematologic system of the performance horse. Pharmacologic alterations in the hematologic and rheologic properties of blood may have an important effect on transport and delivery of oxygen to working muscle during exercise. This article briefly reviews erythropoiesis, hematologic and rheologic responses to training and exercise, and the influence of these alterations on exercise performance. The hemorrheologic and performance effects of hematinics, hematopoietic stimulants, and alterations in blood rheology are discussed. The effects of exercise on blood coagulation, fibrinolysis and platelet function, and the effects of drugs that alter...
Assessment of drug effects on performance. Few definitive studies have been performed that unequivocally demonstrate the ability of a drug to alter the performance of a horse. Nonetheless, the use of drugs in competing horses is regulated worldwide. Drugs have been categorized according to their abuse potential. However, there is still some confusion over what is meant by the terms "performance" and "drug." In the racing community, performance means speed, and fatigue and pain are among its greatest detractors. Speed is most appropriately measured on the racetrack. There are a multiplicity of internal and external variables that influe...
Prejunctional alpha 2-adrenoceptors inhibit acetylcholine release from cholinergic nerves in equine airways. To determine the presence and function of alpha 2-adrenoceptors on cholinergic nerves innervating horse airway smooth muscle, the effects of some alpha 2-adrenoceptor agents on contractions of and acetylcholine (ACh) release from equine airway smooth muscle preparations were studied. Muscle contractions were elicited by either electrical field stimulation (EFS) or exogenous ACh. ACh release was induced by EFS and measured by high-pressure liquid chromatography and electrochemical detection. The alpha 2-adrenoceptor agonists clonidine (10(-7) to 10(-5) M) and UK-14,304 (10(-8) to 10(-6) M) conc...
Pharmacokinetic values of drugs frequently used in performance horses. Tables of values of pharmacokinetic variables (volume of distribution, total body clearance, and plasma elimination half-life) of drugs frequently administered to performance horses are accompanied by explanatory notes. Drugs described include the nonsteroidal anti-inflammatory drugs, corticosteroids, anabolic steroids, central nervous system-modifying drugs, respiratory system drugs, diuretics, local anesthetics, and antibacterial drugs.
The outbreak of equine influenza (H3N8) in the United Kingdom in 1989: diagnostic use of an antigen capture ELISA. In July 1989 influenza A/equine-2 (H3N8) was isolated from a nasopharyngeal swab taken from a non-thoroughbred horse exhibiting acute clinical respiratory disease. This was the first isolation of equine influenza virus in the United Kingdom since 1981. Subsequent investigations of acute respiratory disease in horses indicated that the infection was dispersed throughout the UK. However, unlike the previous epidemic of 1979, the first horses from which the virus was isolated had been vaccinated. This outbreak of influenza provided an opportunity to evaluate an antigen capture ELISA, directed aga...
Equine bronchoalveolar lavage cytology: survey of thoroughbred racehorses in training. Sixty-two Thoroughbred horses aged between 1 and 7 years in training in Sydney had bronchoalveolar lavage (BAL) samples collected for cytological examination. All horses, except the yearlings and those with a cough, had raced at the time of the examination and the trainers reported satisfactory performance. Free erythrocytes were found in 73% of samples and haemosiderophages in 90% of the samples, indicating immediate or past occurrences of exercise-induced pulmonary haemorrhage (EIPH). Bronchoalveolar fluid from the yearlings contained significantly less (P < 0.05) erythrocytes and haemosi...
