Behavioral and Cardiopulmonary Effects of a Constant Rate Infusion of Remifentanil–Xylazine for Sedation in Horses

Xylazine and remifentanil in constant rate infusion (CRI) could be used for sedation in horses without adverse effects. The objective was to evaluate behavioral and cardiopulmonary effects of an intravenous (IV) infusion of xylazine and remifentanil for sedation in horses. Xylazine (0.8 mg/kg IV) followed after 3 minutes by a CRI of xylazine and remifentanil (0.65 mg/kg/h and 6 μg/kg/h, respectively) was administered in 10 healthy horses for 60 minutes. Sedation, ataxia, and cardiopulmonary, hematological, and blood gases variables were evaluated. Heart rate decreased significantly during the first 25 minutes after CRI of xylazine and remifentanil, whereas the respiratory rate showed a significant decrease at 20 minutes and remained significantly low until the endpoint. There were no statistically significant fluctuations in blood arterial pressure, blood pH, partial pressure of arterial carbon dioxide, lactate, creatinine, calcium, chlorine, and sodium, compared with baseline values. Blood partial pressure of arterial oxygen and bicarbonate values were significantly higher compared with baseline values, whereas potassium decreased. Sedation and ataxia developed immediately after the administration of xylazine in all horses. All horses recovered successfully within 10 minutes after interruption of the CRI of xylazine and remifentanil, with no ataxia. No adverse effects were observed. The use of a combination of xylazine and remifentanil as sedation protocol has no adverse effects at the described dosage.     

Effect of Marcha Exercise on Serum Electrolytes and Acid–Base Balance in Mangalarga Marchador Horses

The marcha competition is a functional evaluation, without similar in the world. In this competition, the animals perform marcha at average speed between 9 and 12 km/hr for 50 minutes, covering roughly 6 to 7 km with no rest. The aim of this study was to evaluate and compare the effect of batida gait competition on acid–base balance in Mangalarga Marchador horses during an official marcha competition. The study was conducted on 24 Mangalarga Marchador horses, 12 stallions, and 12 mares (aged 4–6 years and 399 ± 45 kg of body weight). Venous blood samples were collected before and after competition. Blood samples were analyzed for acid–base balance, as well as biochemical and electrolyte parameters. In stallions, a significant (P < .05) postexercise increase in pH, partial pressure of oxygen, bicarbonate concentration, base excess, and glucose was noted. Decrease (P < .05) in pCO₂ (partial pressure of carbon dioxide), chloride and ionized calcium were observed after exercise only in stallions. No changes (P > .05) in hematocrit, hemoglobin, sodium, and potassium were observed after exercise in all animals. The changes in the acid–base balance and electrolyte profile of the Mangalarga Marchador stallions after marcha competition resulted in hypochloremic metabolic alkalosis. Marcha competition did not cause acid–base disturbance in mares. This study enables an evaluation and comparison of physical effort caused by the marcha exercise on acid–base balance in Mangalarga Marchador horses and provides further evidence of the existence of gender differences in sports horses.     

Preliminary Results of Behavioral and Cardiopulmonary Effects of a Constant Rate Infusion of Remifentanil–Xylazine for Sedation in Horses

Standing surgical procedures are performed commonly in horses under sedation. The use of a xylazine and remifentanil combination has not been investigated in horses. We proposed to evaluate behavioral and cardiopulmonary effects of an intravenous (IV) infusion of xylazine with remifentanil for sedation in horses. Xylazine (0.8 mg/kg IV) followed in 3 minutes by remifentanil (0.0005 mg/kg IV), and a constant rate infusion of xylazine and remifentanil (0.65 mg/kg/h; 0.0225 mg/kg/h, respectively) was administered in three horses. Heart rate, respiratory rate (RR), arterial blood pressures, quality of sedation, pH, partial pressure of arterial CO₂ (PaCO₂), partial pressure of arterial O₂ (PaO₂), ataxia, sedation, and sedation overall outcome were assessed. Heart rate and RR remained within normal values during sedation without significant changes from baseline. Systolic, mean, and diastolic arterial blood pressures were increased during sedation. There were no significant changes in pH, PaCO₂, and PaO₂. Sedation developed immediately after injection of xylazine in the three horses but did not increase after remifentanil bolus or IV infusion of both drugs. None of the mares had ataxia. Adverse effects during and after sedation were present: excitement, increase in locomotor activity, and decrease in the gastrointestinal motility. The combination of xylazine and remifentanil sedation protocol produces adverse effects. This protocol cannot be recommended for clinical conditions, at the described doses.     

Effects of Training on Phagocytic and Oxidative Metabolism of Peripheral Neutrophils in Horses Exercised in the Aerobic–Anaerobic Transition Area

Using simple techniques, the neutrophil function, in its phagocytosis and oxidative metabolism stages, was evaluated in horses. This was done before and after moderate exercise at the aerobic-anaerobic threshold (standardized heart rate 150 beats/min and lactate level of 3.07 +/- 0.21 mmol/L). The objective was to determine whether regular training and moderate exercise improved the neutrophil function. A group of 19 horses was used; 11 of these were untrained and the remainder trained for national jumping events. The exercise test consisted of a 5 min trot followed by a 3 min gallop on a long lunge. Blood samples were taken for analysis before, immediately after and 15 min after exercise. The results showed that (a) there is a difference in the internalization of particles (PI, PP and PE) by neutrophils from trained and untrained horses at a single time point during active recovery, and PP is higher in trained horses immediately after exercise; and (b) oxidative metabolism is significantly lower in untrained animals before and 1 min after exercise. The moderate exercise at the aerobic-anaerobic threshold did not have any influence on the peripheral blood neutrophil function of the phagocytosis and oxidative metabolism of particles.     

The Influence of Topically Applied Oil–Based Palatants on Eating Behavior in Horses

Palatants may be added to equine feed and medication either during or after manufacturing to enhance product acceptance. Prior studies have examined a variety of palatants but results have been limited and inconsistent. Therefore, the objective of this research was to evaluate topically applied oil–based palatants on feeding preferences in horses. Stock-type horses (n = 10) were used in this paired preference test across a two-phase study. Phase one compared six palatants (banana, anise, peppermint, apple, spearmint, and orange) to a control (corn oil), whereas phase two compared preference among palatants (anise, apple, and peppermint). Feeding stocks were utilized and horses were allowed 15 seconds for olfaction followed by 3 minutes for consumption. Variables recorded included first diet sniffed and consumed, first action, aversive behaviors, excessive salivation, and consumption. Each trial was also video-recorded and number of chews were counted. Data were analyzed using chi-square and t tests in SAS version 9.4 with P < .05 established as significant. Findings from phase one reveal excessive salivation was observed less frequently (P < .05) for most palatants with the exception of peppermint and orange. Orange negatively impacted palatability indicated by less consumption when compared with the control (P = .02), although there was no impact on chews per gram. No difference between control and treatment diets for first sniff or first consumed was observed when analyzed individually in either phase one or two, although there was a moderate positive correlation (ф = 0.39, P = .04) between olfaction and consumption during the peppermint and anise comparison. Consumption as the first action was consistent across all trials (P < .05). Anise was preferred over apple and peppermint as indicated by higher total consumption (P < .05) in phase two. These data indicate that oil-based palatants can affect feed preferences in horses with increased palatability from anise and decreased palatability from orange flavors.     

Geographic Disparities in Clinical Characteristics of Duodenitis–Proximal Jejunitis in Horses in the United States

Duodenitis–proximal jejunitis (DPJ) is an idiopathic and potentially fatal disease of horses characterized by abdominal pain, proximal intestinal inflammation, and subsequent gastric and small intestinal fluid accumulation. Although this disease is known to be costly and life threatening in the equine industry, the severity of clinical signs can vary widely, and an exact etiology has yet to be elucidated. This study looked to identify differences in clinical parameters of horses with DPJ between geographic regions in an effort to corroborate anecdotal reports and support theories of differing etiologies. Case records were compared from veterinary academic referral hospitals in three different geographic locations in the United States to determine if significant differences in clinical, clinicopathologic, and prognostic characteristics exist among horses with DPJ. Clinical measurements on presentation that were significantly different between regions included heart rate, peritoneal total protein, albumin, anion gap, aspartate aminotransferase, gamma-glutamyl transferase, sodium, chloride, potassium, and creatinine. Duration of hospitalization and maximum body temperature while hospitalized were also different between regions. There were no significant differences in peritoneal cell count, total white blood cell count, neutrophil count, band neutrophils, calcium, total plasma protein, temperature on presentation, duration of reflux, total reflux volume, or age between hospitals. The mortality rates between hospitals were not significantly different. Increased severity of clinical signs and biochemical abnormalities were identified in the Southeastern United States hospital compared with the Northeastern and Western hospitals. A prospective, multicenter case–control study could identify risk factors contributing toward regional differences in this disease in the future.     

Evaluation of the Cranial Cruciate Ligament Repair System? in Surgery for Laryngeal Hemiplegia in Heavy Draft Horses

The purpose of this study was to evaluate the effect of the canine cranial cruciate ligament repair system on laryngeal hemiplegia in heavy draft horses. Twenty-four heavy draft horses diagnosed with grade 4 laryngeal hemiplegia were allocated to either the prosthetic laryngoplasty (PL) group (n=14) or a canine cranial cruciate ligament repair system (CCCLRS) group (n=10). Right to left angle quotients (RLQs) of abductions of the arytenoid cartilages were endoscopically evaluated before and after surgery. Post-operative RLQs in the CCCLRS group were significantly lower than those of the PL group (P<0.01). The canine cranial cruciate ligament repair system was revealed to be a good surgical procedure for laryngeal hemiplegia in heavy draft horses.     

Expression and Activity of Collagenases in the Digital Laminae of Horses with Carbohydrate Overload‐Induced Acute Laminitis

Background

Matrix metalloproteinases (MMP) are hypothesized to degrade structurally important components of the laminar extracellular matrix (ECM) in horses with laminitis.

Objective

To compare levels of expression of stromelysin‐1 (MMP‐3), collagenases (MMP‐1, ‐13), and membrane type‐MMPs (MMP‐14, ‐15, ‐16), and the distribution of their ECM substrates, in laminae of healthy horses and horses with carbohydrate overload laminitis.

Animals

Twenty‐five adult horses.

Methods

Gene and protein expression were determined in extracts of laminae using real‐time quantitative polymerase chain reaction and Western blotting after sodium dodecylsulfate polyacrylamide gel electrophoresis. Distribution of MMP‐13 and ECM components was determined using indirect immunofluorescent microscopy of nonfixed frozen sections. ECM morphology was assessed by hematoxylin and eosin staining.

Results

Of the genes studied, only those encoding MMP‐1 and ‐13 were upregulated in CHO‐induced laminitis; MMP‐1 at Obel grade (OG)1 lameness and MMP‐13 at OG3 lameness. Laminar MMP‐1 was present as 52 kDa proenzyme only. MMP‐13 was present as pro‐ (61 kDa) and processed (48 kDa) enzyme. MMP‐13 localized to the basal epithelium of the secondary epidermal laminae and its increased expression were accompanied by the appearance in secondary dermal laminae (SDL) of multiple foci that were devoid of collagen I, fibronectin, chondroitin and keratan sulfate glycosaminoglycans, and eosin‐staining material.

Conclusions and Clinical Relevance

MMP‐13 is upregulated in laminae of horses with CHO‐induced OG3 lameness and, by degrading components of the ECM, may contribute to the formation of ECM‐free lesions (gaps or tears) that appear in the SDL with OG3 lameness.     

Evaluation of Dynamic Structural Disorders in the Upper Airways and Applied Rein Tension in Healthy Dressage Horses During Riding in Different Gaits and Head–Neck Positions

Flexion of the horse’s head and neck during dressage riding reduces the pharyngeal lumen with the risk of increased upper airway resistance and upper airway obstructions. According to the Fédération Equestre Internationale, hyperflexion is achieved through force, whereas the position low–deep–round is nonforced. The objectives of this study were to evaluate (1) applied rein tension and (2) dynamic structural disorders in the upper airways in dressage horses in different gaits and different head–neck positions (HNPs). Overground endoscopy (OGE) and rein tension were evaluated in 13 clinically healthy and high-performance Warmblood dressage horses while being ridden in a standardized program comprised of four different gaits (halt, walk, trot, and canter) and in four HNPs (unrestrained, competition frame, hyperflexion, and low–deep–round). All included horses were able to achieve the desired HNPs. The HNP low–deep–round showed significantly lower rein tension than competition frame (P < .001) and hyperflexion (P < .001). An association was found between dynamic structural disorders in the upper airway tract evaluated by OGE and head–neck flexion, but this association was not linked to the degree of flexion. The HNP hyperflexion was neither associated with greater rein tension nor severe dynamic structural disorders than the HNP competition frame. This study confirms that low–deep–round is a nonforced position, in contrast to hyperflexion. Further studies are needed to evaluate whether dynamic structural disorders are a result of flexion or if the degree of flexion has an impact.     

Activities of Enzymes Related to the Malate–Aspartate Shuttle in the Blood Cells of Thoroughbred Horses Undergoing Training Exercise

The activities of the enzymes related to the malate–aspartate shuttle, which convert cytosolic NADH into mitochondrial NADH, were measured in red and white blood cells from thoroughbred horses undergoing continuous training (race horses) and compared with those in blood cells from riding horses. The activities of malate dehydrogenase (MDH), a rate-limiting enzyme for the malate-aspartate shuttle, were significantly elevated in the white blood cells (WBC) from race horses compared with those from riding horses. There were no significant differences in the activities of the enzymes in the red blood cells between race horses and riding horses. This increase in the MDH activity in their WBC is considered to reflect the increased metabolic activity in the race horses resulting from the training.     

Repeatability and Intra‐ and Inter‐observer Agreement of Cervical Vertebral Sagittal Diameter Ratios in Horses with Neurological Disease

Background

Sagittal ratio values (SRVs) of cervical vertebrae are used for ante‐mortem diagnosis of cervical vertebral stenotic myelopathy, but intraobserver and interobserver variability in measurement may influence radiographic interpretation of vertebral stenosis in horses with neurological disease.

Objectives

To determine intraobserver repeatability in SRVs, intra‐ and interobserver agreement in SRVs and whether or not agreement was influenced by animal age.

Animals

Forty‐two horses (>1 year old) with neurological disease from which laterolateral computed radiographic images of C2–C7 were obtained.

Methods

Four observers made measurements from C2 to C7 for each horse and interobserver agreement for intra‐ and intervertebral SRVs was determined using Bland–Altman analysis (acceptable agreement: limits of agreement [LOA] ≤ 0.05) on all horses and those ≤3 (n = 25) and >3 (n = 17) years old. Each observer also made repeated measurements for 10 horses and intraobserver repeatability and agreement were determined.

Results

Adequate intraobserver repeatability was achieved for 6 sites. Within observers, paired measurements had a median difference ≤5.7%, but a large range in differences often occurred, most frequently at intervertebral sites. For C5, C6, C7, and C3–4, LOA ≤ 0.05 were achieved by at least 1 observer. With the exception of C5 for 1 pair, LOA were >0.05 for interobserver agreement, regardless of animal age. LOA were largest at intervertebral sites.

Conclusions and Clinical Importance

Within and between observers, measurement error may limit the diagnostic accuracy of SRVs and result in discrepancies of diagnosis and treatment and warrants consideration when used clinically in horses with neurological disease.     

Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry (MALDI-TOF MS) for Identification of Bacterial Isolates From Horses

Matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) is used for bacterial identification by analyzing the spectra of isolates and comparing them against a database of reference spectra; it is known for its rapidity and accuracy. Although MALDI-TOF MS is used for identification of bacterial isolates from animals, not all animal pathogens are identified correctly. In this study, we used a commercial MALDI-TOF MS identification system to examine 3724 bacterial isolates from horses and their environments. Isolates that could not be identified with MALDI-TOF MS were identified by 16S rRNA gene sequence taxonomic analysis. MALDI-TOF MS could identify 86.2% of the isolates from horses to the species level, showing that this method could be successfully applied for bacterial identification in horses. However, some species known to be equine pathogenic agents including Taylorella equigenitalis and Rhodococcus equi were difficult to identify with MALDI-TOF MS, which might be the result of an inadequate reference database. Some Prevotella, Staphylococcus, and Streptococcus isolates, which could not be identified with either MALDI-TOF MS or 16S rRNA gene sequencing analysis, formed clusters in the 16S rRNA phylogenic tree, and might be unknown species isolated from horses. Adding the spectra of isolates identified in this study to an in-house database might make MALDI-TOF MS a more useful tool for identifying equine isolates.     

Circulating β-Endorphin,Adrenocorticotropin, and Cortisol Concentrations of Horses Before and After Competitive Show Jumping with Different Fence Heights

Circulating β-endorphin, adrenocorticotropin, and cortisol concentrations were studied before and after competitive show jumping in 18 trained jumper horses aged between 11 and 13 years and having the same level of show experience. Horses were subjected to the same type of management and daily training exercise. Each horse had been ridden by the same rider during both the daily training exercise and show jumping event. All horses, randomly divided into three groups paired by gender, performed in three competition levels with the same circuit design over 10 fences, with 5 upright and 5 cross-pole fences, differing for the fence height: group I (n = 6), 1.10 m; group II (n = 6), 1.20 m; and group III (n = 6), 1.30 m. Repeated measures analysis of variance showed a statistically significant effect of competitive exercise on β-endorphin and cortisol changes in all groups, whereas the effect of exercise on adrenocorticotropin changes was exclusively seen in groups II and III. Two-way repeated measures analysis of variance showed that the effect of fence height was significant (P = .03), and time (P = .0001) also affected cortisol changes. These results suggest that the hypothalamic-pituitary-adrenal axis response is different with respect to the different fence heights of jumping course and the different time points of the recovery period.     

Effects of β-Hydroxy-β-Methylbutyrate and γ-Oryzanol on Blood Biochemical Markers in Exercising Thoroughbred Race Horses

In both the horse and the man, nutritional ergogenic aids have been used to improve physical ability in conjunction with an appropriate training regimen. Although training increases physical condition, the ease of taking a nutritional additive to improve training results explains the demand for supplementation, which may increase mechanical energy of work, delay onset of fatigue, or improve neuromuscular coordination. The purpose of this study was to determine the effects of oral supplementation of β-hydroxy-β-methylbutyrate (HMB) and γ-oryzanol (GO) on indices of exercise-induced muscle damage in Thoroughbred race horses. In this 32-week study, the horses were assigned to either a placebo, GO (3.0 g/d), HMB (15 g/d), or GO and HMB treatment groups. The supplements were administered for the first 16 weeks of the study during the training period before the racing season began. Blood samples were taken at baseline, and then during training, before exercise, immediately after exercise, and 30 minutes after exercise. Heart rate and speed were monitored in each exercise session. Hematocrit, glucose, lactate (LA), creatine phosphokinase, and aspartate aminotransferase were measured before and after each exercise session. Analysis of variance showed a significantly greater increase in postexercise creatine kinase activity in placebo-supplemented group than in the other treatment groups, both in the training period and during the racing seasons (P < .05). Blood LA was higher immediately after exercise in the placebo group compared with the supplemented groups. In conclusion, supplementation with HMB and GO resulted in decreased creatine kinase and LA after exercise. These findings support the hypothesis that HMB and GO supplementation helps to prevent exercise-induced muscle damage.     

Gender Differences–Induced Changes in Serum Hematologic and Biochemical Variables in Mangalarga Marchador Horses After a Marcha Gait Competition

The aim of this study was to investigate whether marcha exercise results in changes in serum hematologic and biochemical variables and whether this condition differs in male and female horses. Thirty-five Mangalarga Marchador horses, 18 males and 17 females were included in the study. Blood samples were obtained before and immediately after a marcha competition. Samples were used for measurement of hematocrit (HCT), hemoglobin concentration (HGB), red blood cell (RBC), total and differential white blood cell (WBC), total protein (TP), albumin (Alb), aspartate aminotransferase (AST), gamma glutamyltransferase (GGT), creatine kinase (CK), alkaline phosphatase (ALP), lactate dehydrogenase (LDH), creatinine (Crea), and urea (BUN) levels. Data were submitted to analysis of variance using the SAS statistical program, and means were compared by the Tukey test (P < .05). In both males and females, RBC, HCT, AST, and GGT activity increased in response to exercise, but there were no significant differences between genders. In females, significant increases in TP, BUN, Crea, CK, and LDH levels were detected after the marcha gait, but no such changes were detected in males. Total WBC concentrations increased in response to the exercise in both, males and females; however, there were no differences between genders. Plasma HGB, Alb, and ALP levels after marcha gait did not differ in both genders. Marcha exercise–induced significant hematologic and biochemical changes in serum of Mangalarga Marchador horses, independently of gender. However, females presented more blood changes after marcha gait. Gender differences should be taken into consideration in experiments with athletic horses.     

Do Muscle Activities of M. Splenius and M. Brachiocephalicus Decrease Because of Exercise-Induced Fatigue in Thoroughbred Horses?

Muscle activities of the major hindlimb muscles have been reported to decrease with fatigue in horses. However, those in other muscles have been scarcely reported. We aimed to quantify fatigue-induced electromyographic changes in head and neck muscles and muscles around the shoulder joints in horses. Surface electromyographic recording of the splenius, brachiocephalicus, infraspinatus, and deltoid muscles was performed on a total of nine healthy Thoroughbred horses. Horses galloped on a treadmill inclined to 3% at a constant speed (12.7–14.6 m/second) to make them fatigued after approximately 5 minutes. They trotted at 3.5 m/second before and after this exercise. Stride frequency, integrated electromyographic values for a stride, and median frequency of the muscle discharge were calculated every 30 seconds. These parameters were compared at the start and end of the gallop exercise for the lead and trailing limbs and while trotting before and after the exercise using a paired t-test. The stride frequency significantly decreased at the end of the gallop (P < .001), whereas it did not change while trotting. Integrated electromyographic values of the splenius and brachiocephalicus muscles in both lead and trailing limbs at the gallop and those of both left and right sides at the trot significantly decreased with fatigue (P < .05), whereas those of infraspinatus and deltoid muscles did not change at either gallop or trot. No changes were observed in median frequency in any muscles with fatigue. These results suggest that splenius and brachiocephalicus muscle activities can be associated with stride frequency and speed.     

Growth Hormone and Prolactin Secretion in Horses: Effects of Multiple and Extended Exercise Bouts, β-Hydroxy-β-Methyl Butyrate Feeding,and Arginine and Thyrotropin-Releasing Hormone Pretreatment

Five experiments were performed to test the overall hypothesis that exercise might be a useful indicator of growth hormone (GH) and prolactin status in horses. In experiment 1, geldings were exercised for 5 minutes four times at hourly intervals. The prolactin response (P < .05) to the first two exercise bouts was small and increased with successive bouts. There was a consistent GH response (P < .05) for only the first two bouts. In experiment 2, geldings were exercised for 29 to 39 minutes on a treadmill. After the initial bout, half the geldings were supplemented daily with Ca-β-hydroxy-β-methyl butyrate, and all geldings were conditioned for 12 weeks. Exercise bouts at 7 and 12 weeks indicated no effect (P > .1) of supplementation. In experiment 3, treatment of geldings with arginine before exercise increased (P < .001) prolactin concentrations but had no effect (P > .1) on the GH response to exercise. In experiment 4, the repeatability of the GH response to 5 minutes of exercise was determined by exercising eight stallions on six separate occasions. In addition to a large variation in GH response among stallions, there was a large variation within each stallion. In experiment 5, pretreatment with thyrotropin-releasing hormone 2 hours before exercise did not normalize the GH response to exercise. In conclusion, factors affecting the GH response to exercise likely preclude its usefulness as an indicator of GH status in horses.     

Induction of anesthesia and recovery in donkeys sedated with xylazine: a comparison of midazolam–alfaxalone and midazolam–ketamine

Objective

To compare the induction and recovery characteristics and selected cardiopulmonary variables of midazolam–alfaxalone or midazolam–ketamine in donkeys sedated with xylazine.