Effect of dietary cation-anion difference on acid-base status and energy digestibility in sedentary horses fed varying levels and types of starch

Six mature horses were used in a 6×6 Latin Square design experiment to study the effects of varying dietary cation-anion differences (DCAD) on the acid-base status and energy digestibility of horses fed varying levels and sources of starch. Rolled corn, whole oats, or dehydrated alfalfa meal were used to make up the concentrate portions of the diets. Three diets had a DCAD above 300 meq/kg DM, and three below 160 meq/kg DM. This trial consisted of 11-day adjustment periods followed by 72-hour experimental collection periods. During that time, venous blood samples were drawn for analysis of pH, pCO₂, HCO₃⁻, pO₂, and lactate concentrations. Total urine was collected and measured for pH and mineral content. Representative feed and fecal samples were taken to determine energy digestibility. Blood lactate concentration showed no variation among treatments. Energy digestibility showed no variation with respect to DCAD, but did vary with starch intake. Urine pH, blood pH and blood HCO₃⁻ concentrations were significantly lower for horses consuming diets with a low DCAD as compared with high DCAD diets regardless of starch source or intake. Thus, it may be possible to reverse any metabolic acidosis caused by high starch intake by increasing the DCAD of the diet.     

Effects of dietary cation-anion balance on blood PH, acid base parameters, serum and urine mineral levels, and parathyroidhormone (PTH) in weanling horses.

This study demonstrated that the feeding of treatment diets with calculated dietary cation-anion balances (DCAB) of +370.43 (H) and -25.69 (L) did not have significant effects on blood pH, pCO₂, and HCO₃-. Serum Ca²⁺, P, Na⁺, and Cl^- as well as plasma PTH did not differ (P > .05) between the two treatment groups. Serum K⁺ was higher (P< .05) in horses fed diet H rather than diet L. The DCAB of the diet significantly affected urinary Ca²⁺, P, Na⁺, K⁺, and Cl^- excretion in the young growing horse. Urine Ca²⁺ and Cl- levels were higher (P < .01) in horses fed diet H versus diet L. Furthermore, levels of P, Na⁺, and K⁺ in the urine were higher (P < .01) in horses on diet H as opposed to diet L. Results of this study indicate that horses were able to maintain acid-base status regardless of diet. However, these data imply that growing horses consuming diets low in DCAB may be predisposed to abnormal bone mineralization due to the increase in calcium excretion which could lead to a weakening of the skeletal system.     

ImproWin? in the treatment of gastric ulceration of the squamous mucosa in trotting racehorses

Background

Gastric ulceration is highly prevalent in horses, and there is a large commercial market for feed-additives and non-licenced products that claim effect for prevention and treatment of gastric ulceration. ImproWin® has been used as a feed additive in horses with anecdotal evidence that it may have some positive effects on gastric ulceration.The aim of this study was to investigate the effect of ImproWin® treatment on spontaneously occurring gastric ulcers of the squamous mucosa in Standardbred and Coldblooded trotting racehorses.The study was performed as a randomised, double-blinded, single centre study with stratified semi cross-over design with breed as stratification factors. The horses were clinically and endoscopically examined prior to start and after three weeks of treatment. The ulcerations were scored in accordance with Equine Gastric Ulcer Council (EGUC) recommendations on a 5 point scale and on a 10 cm Visual Analogue Scale (VAS). The patients were responder-classified after 3 weeks. Responders in need of ulcer treatment were randomly allocated to 2 or 4 weeks of additional treatment. Non-responders to placebo were crossed to ImproWin®.

Results

The 5-point EGUC score and VAS recorded score was significantly reduced (P ≤ 0.01) in both groups after 3 weeks of treatment. From 3 weeks to the end of treatment the score was further significantly reduced in the ImproWin® group (P ≤ 0.05).At the end of treatment, 78% in the ImproWin® group and 54.8% in the placebo group were classified as responders. The difference was significant (P = 0.04).

Conclusions

ImproWin® may aid the healing process of ulcers of the gastric squamous mucosa of trotters.     

Effects of Intermittent Positive Pressure Ventilation on Cardiopulmonary Function in Horses Anesthetized with Total Intravenous Anesthesia Using Combination of Medetomidine,Lidocaine, Butorphanol and Propofol (MLBP-TIVA)

Effects of intermittent positive pressure ventilation (IPPV) on cardiopulmonary function were evaluated in horses anesthetized with total intravenous anesthesia using constant rate infusions of medetomidine (3.5 µg/kg/hr), lidocaine (3 mg/kg/hr), butorphanol (24 µg/kg/hr) and propofol (0.1 mg/kg/min) (MLBP-TIVA). Five horses were anesthetized twice using MLBP-TIVA with or without IPPV at 4-week interval (crossover study). In each occasion, the horses breathed 100% oxygen with spontaneous ventilation (SB-group, n=5) or with IPPV (CV-group, n=5), and changes in cardiopulmonary parameters were observed for 120 min. In the SB-group, cardiovascular parameters were maintained within acceptable ranges (heart rate: 33–35 beats/min, cardiac output: 27–30 l/min, mean arterial blood pressure [MABP]: 114–123 mmHg, mean pulmonary arterial pressure [MPAP]: 28–29 mmHg and mean right atrial pressure [MRAP]: 19–21 mmHg), but severe hypercapnea and insufficient oxygenation were observed (arterial CO₂ pressure [PaCO₂]: 84–103 mmHg and arterial O₂ pressure [PaO₂]: 155–172 mmHg). In the CV-group, normocapnea (PaCO₂: 42–50 mmHg) and good oxygenation (PaO₂: 395–419 mmHg) were achieved by the IPPV without apparent cardiovascular depression (heart rate: 29–31 beats/min, cardiac output: 17–21 l /min, MABP: 111–123 mmHg, MPAP: 27–30 mmHg and MRAP: 15–16 mmHg). MLBP-TIVA preserved cardiovascular function even in horses artificially ventilated.     

Reduced high intensity training distance had no effect on VLa4 but attenuated heart rate response in 2-3-year-old Standardbred horses

Background

Training of Standardbred race horses aims to improve cardiovascular and metabolic functions but studies on the effects of different training strategies from breaking till racing are lacking. Sixteen horses with the goal to race as 3-year-olds were studied from breaking (1-year-olds) to December as 3-year-olds. Horses were allocated to either a control (C) or reduced (R) training program from 2 years of age. The aim was to evaluate the effect of reducing the distance of high intensity exercise by 30% with respect to velocity at lactate concentration 4 mmol/l (V_La4), blood lactate and cardiovascular response. All training sessions were documented and heart rate (HR) was recorded. A standardized exercise test of 1,600 m was performed 10 times and a V_La4 test was performed five times.

Results

C horses initially exercised for a longer time with a HR >180 beats per minute compared to R horses (P < 0.05) but after 6–9 months, time with HR >180 bpm decreased in C and were similar in the two groups (P > 0.05). Over the 2-year period, recovery HR after the 1,600 m-test decreased in both groups but was within 2 months lower in C than in R (P < 0.05). C horses also had lower resting HR as 3-year-olds (P < 0.01) than R horses. In C, post exercise hematocrit was higher than in R (P < 0.05). There was a tendency (P < 0.1) towards a larger aortic diameter in C as 3-year-olds (C: 1.75 ± 0.05, R: 1.70 ± 0.05 cm/100 kg BW). Left ventricle diameter and blood volume (in December as 2-year-olds) did not differ between groups. There were no differences between groups in post exercise blood lactate concentration or in V_La4. Both groups were equally successful in reaching the goal of participation in races.

Conclusions

Horses subjected to a reduced distance of high intensity training from the age of 2 showed an attenuated heart rate response, but were able to maintain the same V_La4 and race participation as horses subjected to longer training distances.     

Comparison of Caudal Epidural Anesthesia with Lidocaine-distilled Water and Lidocaine-MgSO4 Mixture in Horses

This study was performed to compare the onset and duration of analgesia produced by either a lidocaine−MgSO₄ or lidocaine−distilled water combination administration in the caudal epidural space of horse. Seven healthy adult horses, aged 11.7 ± 1.4 years (mean ± SD), body weight (kg) 567 ± 32.5 (mean ± SD), were selected for this study. Caudal epidural anesthesia was produced in all horses by administering 2% lidocaine (0.22 mg/kg) diluted in 1 mL distilled water and repeated with 2% lidocaine (0.22 mg/kg) diluted in 1 mL 10% MgSO₄ 2 weeks later. Time to onset (minutes), duration (minutes), and cranial spread of epidural analgesia were recorded. Heart rate (HR), respiratory rate (RR), and body temperature (°C) were recorded. Measurements were taken at 0 (as a baseline value before epidural administrations) and at 5, 10, 15, 30, 60, and 75 minutes after the epidural administrations of each treatment. Statistical analyses included paired Student t test and analysis of variance (computer program SPSS, Analytical Software, version 15.00). Statistical significance was set at P < .05. Onset of analgesia was significantly different (P < .001) between lidocaine-distilled water (2.38 ± 0.47 minutes) and lidocaine−MgSO₄ (4.62 ± 0.54 minutes). Duration of analgesia after lidocaine−MgSO₄ (186.0 ± 7.0 minutes) was longer than lidocaine-distilled water (54.5 ± 7.3 minutes). No significant differences were recorded for HR, RR, and body temperature in comparison with baseline values for each group. Using the lidocaine−MgSO₄ combination for obstetric and surgical procedures could commence relatively soon after epidural injection and could be completed without readministration of anesthetic agent.     

Arterial Acid-Base Measurements in 1–3 Days Old Piglets

A method of percutaneous arterial blood sampling in piglets has been developed and determinations of arterial pH, pCO₂, pCO2, BE, HGO3 , LA and Hb have been performed in 121 piglets 1–3 days of age. The validity of these measurements has been tested and proved valid for clinical practice with the exception of pO₂ and LA values. The correlations with age were statistically significant but poor and therefore the mean values are presented as reference values. These were: pH: 7.423±0.082, PCO₂: 4.98±0.74 kPa, BE: 0.4±4.1 mmol/1, HCO³_‒: 23.0+3.2 mmol/1 and Hb: 88±14 g/1.     

Measurement of erythrocyte carbonic anhydrase isozymes (CA-I and CA-II) in racehorses and riding horses

Equine carbonic anhydrase isozymes (CA-I and CA-II) were purified from erythrocytes by several column chromatography. Polyclonal anti-CA-I and anti-CA-II sera were produced in rabbits. Sensitive competitive enzyme-linked immunosorbent assays (ELISA) were established to determine the developmental changes in CA-I and CA-II levels in equine erythrocytes. Concentrations of CA-I and CA-II in erythrocytes from 150 clinically normal thoroughbreds (123 racehorses and 27 riding horses) were determined by ELISA. Mean (+/- SD) concentrations of CA-I and CA-II in racehorses were 1.70 +/- 0.48 and 0.94 +/- 0.13 mg/g hemoglobin (Hb), respectively. Mean concentrations of CA-I and CA-II in riding horses were 2.34 +/- 0.52 and 0.76 +/- 0.08 mg/g Hb, respectively. When the CA levels in racehorses and riding horses were compared, the CA-I level in riding horses was higher than that in racehorses (p=0.01). The CA-II level in racehorses was higher than that in riding horses (p=0.02). These data suggest that the levels of CA isozymes in erythrocytes of racehorses were influenced by chronic physical stress. The CA-I concentration in erythrocytes of 2-month-old horses was approximately 0.25 mg/g Hb. The CA-I level noticeably increased during the first year of life and approached normal adult levels by 2 years. The CA-II level decreased slightly with age, indicating different regulation of CA-I and CA-II expression during development.     

Variations in muscle fiber composition between successfully and unsuccessfully raced quarter horses

Muscle biopsy samples were removed from the m gluteus medius of 47 retired running Quarter Horse (QH) mares. Horses were separated based on bloodline, past racing history and percentage Thoroughbred (TB). The bred to run and raced (BRRA) and bred to run and not raced (BRNR) groups possessed a lower percentage (P<.01) of fast-twitch low oxidative (FT) fibers (BRRA 38.6 and BRNR 36.2±2.54 respectively). These horses also possessed a higher percentage (P<.01) of fast-twitch high oxidative (FTH) fibers (BRRA 52.5 and BRNR 48.5±2.54, respectively) than not bred to run and not raced (NBNR) horses. Horses that were bred to run had higher (P<.05) FTH to FT fiber ratios (1.44) than horses that were not bred to run (.94). Successful racehorses possessed a lower percentage (P<.05) of slow-twitch (ST) fibers and a higher percentage (P<.05) of FT fibers than unsuccessful racehorses. Success or failure was determined by Speed Index. No differences (P>.05) were found in the percentage FTH fibers between successful and unsuccessful horses.     

Tall fescue utilization by exercised - yearling horses

Little information has been published concerning the effects of endophyte-infected tall fescue consumption on performance of young growing horses. Therefore, this study evaluated exercise performance and growth by yearlings fed endophyte-infected fescue. Twelve Quarter Horse yearlings (12-16 months of age) were blocked by age and sex and randomly assigned to one of three groups. Group I received native prairie hay (P), Group II received endophyte-free fescue hay (EF) and, Group III received endophyte infected fescue hay (EI). Rectal temperatures were monitored daily and growth parameters (weight, hip and wither heights, and body fat) were measured at the start of the study (d 0) and every 2 weeks throughout the 106 d study. Additionally, blood samples were collected on d 0 and every 28 d for the duration of the study to monitor blood concentrations of calcium, phosphorus, prolactin (PRL), thyroxine (T₄), and triiodothyronine (T₃). Horses were exercised twice a week for 10-30 min. Respiration, heart rate, and rectal temperature were measured at the start and 5, 30, and 60 min postexercise. Growth parameters and daily rectal temperatures were not different (P >.05) among grdups. No differences (P >.05) occurred among groups in concentrations of serum calcium, phosphorus, PRL, T₃, and T₄. Respiration rates were lower (P <.05) at 30 and 60 rain postexercise for horses consuming fescue than for horses consuming prairie hay. Postexercise heart rates and rectal temperatures showed no difference (P <.05) among groups. These data suggest that young growing horses being exercised can utilize endophyte-infected fescue efficiently on a short-term basis.     

Differences in need for hemodynamic support in horses anesthetized with sevoflurane as compared to isoflurane

OBJECTIVE: To study whether hemodynamic function in horses, particularly mean arterial blood pressure (MAP), is better maintained with sevoflurane than isoflurane, thus requiring less pharmacological support. STUDY DESIGN: Prospective randomized clinical investigation. Animals Thirty-nine racehorses undergoing arthroscopy in lateral recumbency. METHODS: Horses were assigned to receive either isoflurane (n = 20) or sevoflurane (n = 19) at 0.9-1.0 minimum alveolar concentration (MAC) for maintenance of anesthesia. Besides routine clinical monitoring, cardiac output (CO) was measured by lithium dilution. Hemodynamic support was prescribed as follows: when MAP decreased to <70 mmHg, patients were to receive infusion of 0.1% dobutamine, which was to be discontinued at MAP >85 mmHg or heart rate >60 beats minute(-1). Statistical analysis of results, given as mean +/- SD, included a clustered regression approach. RESULTS: Average inhalant anesthetic time [91 +/- 35 (isoflurane group) versus 97 +/- 26 minutes (sevoflurane group)] and dose (in MAC multiples), volume of crystalloid solution infused, and cardiopulmonary parameters including CO were similar in the two groups, except heart rate was 8% higher in isoflurane than sevoflurane horses (p < 0.05). To maintain MAP >70 mmHg, isoflurane horses received dobutamine over a significantly longer period (55 +/- 26 versus 28 +/- 21% of total anesthetic time, p < 0.01) and at a 51% higher dose than sevoflurane horses (41 +/- 19 versus 27 +/- 23 microg kg(-1) MAC hour(-1); p = 0.058), with 14/20 isoflurane animals and only 9/19 sevoflurane horses being infused with dobutamine at >30 microg kg(-1) MAC hour(-1) (p < 0.05). Dobutamine infusion rates were consistently lower in the sevoflurane as compared to the isoflurane group, with differences reaching significance level during the 0-30 minutes (p < 0.01) and 61-90 minutes periods (p < 0.05). CONCLUSIONS AND CLINICAL RELEVANCE: Horses under sevoflurane anesthesia may require less pharmacological support in the form of dobutamine than isoflurane-anesthetized horses. This could be due to less suppression of vasomotor tone.     

Retrospective trainer-reported incidence and predictors of health and training-related problems in standardbred racehorses

Information on the incidence of injury, illness, and unexplained loss of athletic performance of 2345 Standardbred racehorses was gathered from a telephone survey of 177 trainers during the 1996-1997 season. Trainer-reported incidence of infection and illness (18%) was higher than the incidence of musculoskeletal problems (10%) or unexplained athletic performance loss (6%). Older horses (>5 years) were more likely to develop musculoskeletal problems (odds ratio [OR] = 3.9; confidence interval [CI] = 1.8-8.2) and performance loss OR = 2.3, CI = 1.1-5.2) than 2-year-old horses. Horses were more likely to suffer musculoskeletal problems if fast-worked on tracks or surfaces with no banking compared with those fast-worked on tracks with banking similar to commercial racetracks OR = 4.6, CI = 2.0-9.9). Horses given no warm-up before high-intensity exercise were more likely to suffer a musculoskeletal problem than horses given a light warm-up of 1 to 9 minutes OR = 2.5, CI = 1.5-4.4). Horses trained for more than 164 min·wk⁻¹ were more likely to suffer musculoskeletal problems OR = 1.7, CI = 1.1-2.8) and athletic performance loss OR = 2.5, CI = 1.4-4.4) than horses trained for shorter periods. Horses given a moderate weekly exercise duration (132-148 min·wk⁻¹) had the lowest rates of infection and illness, but short (114-131 min·wk⁻¹) or very long (>164 min·wk⁻¹) weekly exercise duration increased the risk of horses suffering infection and illness OR = 1.6, CI = 1.1-2.2 and OR = 1.3, CI = 1.0-1.9, respectively). We conclude that Standardbred trainers could avoid many training and health problems by using well-banked tracks, providing a proper warm-up, and avoiding excessive training.

Introduction

Racehorses suffer from a variety of health and training problems that may result in poor performance. Musculoskeletal injury is a major problem in Thoroughbred racehorses, accounting for as much as 53% of the lost training and racing days.[1 and 2] Thoroughbreds that race too often, [2 and 3] have insufficient training before racing, [4] or perform too much high-speed work [5] have a greater risk of musculoskeletal problems. Performance may also be affected by respiratory infection, which is responsible for 12% of lost training or racing days. [1]Poor performance can also develop in an otherwise apparently healthy horse. Such unexplained loss of athletic performance may arise from undiagnosed health problems or from too much training.[6] Overtraining described as a state of prolonged fatigue caused by too much training or insufficient recovery [7] has been demonstrated in horses in both cross-sectional and longitudinal studies, [8 and 9] but the incidence of athletic performance loss because of overtraining in the population is unknown. Recently reported prospective studies that used the same group of horses has found that overtraining appeared to be difficult to induce in horses, [10, 11, 12 and 13] which may indicate that overtraining accounts for little of the loss in athletic performance suffered by Standardbred racehorses.It is thought that lameness is the most important cause of poor racing performance in Standardbreds[14]; however, the incidence of musculoskeletal problems causing lameness in Standardbreds is lacking. There is also little information on the incidence of respiratory disease or athletic performance loss in Standardbreds. The purpose of this study was to determine the trainer-reported incidence of these problems in Standardbred racehorses and to reveal any association with factors such as sex, age, ability, training, track surface, and track design.

Materials and methods

A survey was administered by telephone to 177 Standardbred racehorse trainers randomly selected from a list of 300 trainers compiled by Harness Racing New Zealand. The survey was administered at the end of the 1996-1997 racing season, which lasts from about September through June, and questions asked during the survey related to the 1996-1997 racing season. Trainers were asked to recall the total number of horses that experienced an unexplained and consistent loss of athletic performance (“performance decrease that lasted for at least two weeks, which was not obviously as a result of tying up, infection, illness, or musculoskeletal problems”). Trainers were also asked for the total number of horses that suffered infection or illness (viral and bacterial infections and respiratory diseases but not bleeding from the lungs), and musculoskeletal problems (lameness caused by muscle, tendon, bone, or back injuries that resulted in lost training days). Pilot work involved testing the questionnaire on 10 local horse trainers; from their feedback and that of other colleagues and horse trainers, more than 11 revisions were made. The interview consisted of 65 questions and lasted approximately 20 minutes. The incidences of performance loss and health problems detailed in this study are trainer-diagnosed; however, in the majority of cases (80%), the horses were also examined by a veterinarian and their diagnosis was consistent with the trainer's. Unfortunately, full details of the veterinary examination were not obtained during this study.To examine the influence of track design and banking, trainers were asked to compare the banking of their training tracks to the banking of a commercial racetrack (Forbury Park Raceway, Dunedin, New Zealand, which had a banking angle of approximately 2.3 degrees). Trainers had to decide whether the banking of their track was more, less, or about the same as the banking of the commercial track. Because of the need to keep the questionnaire to a reasonable size, in-depth training data was collected on only one particular group of horses—qualified maidens. Qualified maiden racehorses (previously raced but unplaced) represent the largest group of racehorses in training in New Zealand. Trainers were also asked whether they trained their other horses (faster, slower, unqualified, 1-7, or >7 wins) any differently from the qualified maidens. Information on training type, duration, and intensity were gathered for each day of a typical training week. Exercise duration and total training workload was divided into quintiles (5 equal sections) and contrasts between the quintiles were then examined. Trainers were specifically asked about the duration of the warm-up, which was not included in the total training time. Warm-up was defined as the initial preparatory phase of a training session in which the horse is slowly accustomed to low-intensity exercise and prepared for further high-intensity exercise.Although it is acknowledged that career wins is a crude method of assessing racing ability, it was the most appropriate method available to the researchers during a phone interview that gave some indication of horses' ability. Trainers were therefore asked about the number of wins for each horse and horses were grouped according to the total number of career wins. The Human Ethics Committee of the University of Otago reviewed and approved this project (reference number 97/049).The survey data were analyzed using a repeated-measures general modeling procedure (Proc Genmod, SAS Institute, Cary, NC), which estimated the effect of age, sex, gait, number of wins, warm-up, track design, training duration, and workload as odds ratios ORs). The OR is a way of comparing whether the probability of a certain event is the same for two groups. An OR of 1 implies that the event is equally likely in both groups, whereas an OR of more than one implies that the event is more likely in the first group compared with the second. For example, the odds of a horse suffering a musculoskeletal injury if fast-worked on tracks with no banking is 0.52 (cases/noncases = 12 injured/23 noninjured), whereas the odds of a horse suffering a musculoskeletal injury on well-banked tracks is 0.11 (37 injured/329 noninjured). Therefore, the OR is 4.6 and is interpreted as: 4.6 horses suffer a musculoskeletal injury if fast-worked on an unbanked track compared with every 1 horse that suffers the same injury when fast-worked on well-banked tracks. Proc Genmod (SAS Institute) analyzed the total number of horses in a particular subgroup and the total number of problems in the same subgroup for each trainer. A type I error of 5% was chosen for declaration of statistical significance; precision of estimates was represented by the 95% confidence interval (CI), the likely range of the true value.To estimate the reliability of the trainer's responses, a second questionnaire identical to the first was administered to 17 randomly selected trainers from the same sample 8 months after the original survey. The trainers' responses to the same questions from separate surveys given 8 months apart were used to gauge reliability of the survey. Questions on the sex, gait, and number of race wins of the horses under the trainers' care that suffered health and training-related problems were analyzed. These variables represented population characteristics of the horses that could change with time as horses entered or left the trainers stables, and therefore affect the reliability of the reported data. Survey reliability was found by comparing the empirical standard error of the odds ratio from the initial (Main) and second (Rely) surveys after adjustment for sample size. When the empirical standard error was similar (within one decimal place) between studies, then reliability was considered low, but when the empirical standard error was smaller in the Rely survey compared with the Main survey, then the reliability of the survey was acceptable.

Results

Overall training and health problems

Horses were 2.1 times more likely to suffer from infections and illness than from musculoskeletal problems (CI = 1.4-2.8, P < .001) and musculoskeletal problems were 1.7 times more likely to occur than athletic performance loss (CI = 1.2-2.3, P < .001). Horses that had no recognized problems raced 12 ± 6 times (mean ± SD) over the main racing season (September 1996-June 1997).

Athletic performance loss

Sixty-eight trainers reported that a total of 146 horses developed a decrease in athletic performance not readily associated with musculoskeletal injury, illness, or tying-up during the season (6% of the 2345 horses sampled). Most horses (78%) that suffered athletic performance loss required at least 6 weeks to recover to normal form; the remaining 22% recovered within 4 weeks. In general, the decrease in athletic performance occurred towards the middle and end of the racing season. The incidence of athletic performance loss in the various subgroups of horses is shown in Table 1, and the ORs and confidence limits for statistically significant differences in incidence within each subgroup are shown in Table 2.     

Measurement of Carbonic Anhydrase I and II Isozymes in Feces as a Marker of Occult Blood in Horses with Intestinal Tract Bleeding

Although endoscopy is the definitive diagnostic method for the detection of colonic ulcers, the equipment required for performing the test is costly and difficult to use. Therefore, a simple cost-effective and reliable screening test for intestinal tract bleeding is needed. To this end, we measured carbonic anhydrase isozymes (CA-I and CA-II) originating from erythrocytes by ELISA in order to determine if they could be used as markers of occult blood in feces. For fecal extract preparation, 2 g of feces were mixed with 4 ml of 0.01 M Tris-HCl (pH 8.0) containing 0.01% thimerosal. The concentrations of CA-I and CA-II in the fecal samples of 13 clinically normal racehorses were found to be 30.0 ± 10.0 and 34.0 ± 13.0 ng/ml, respectively. Increased concentrations of CA-I were detected in the fecal samples of 5 horses after blood administration; however, no increase was observed in CA-II. The concentrations of CA-I and CA-II in the fecal samples of 88 racehorses with clinical signs of equine gastric ulcer syndrome (EGUS) were 115.3 ± 79.0 and 41.0 ± 42.0 ng/ml, respectively. Thus, our results indicate that CA isozymes can be useful as markers of occult blood in the fecal samples of horses with intestinal tract bleeding.     

Age‐related differences in prostaglandin E2 synthesis by equine cartilage explants and synoviocytes

Briston, L., Dudhia, J., Lees, P. Age‐related differences in prostaglandin E₂ synthesis by equine cartilage explants and synoviocytes. J. vet. Pharmacol. Therap. 33 , 268–276. Time‐ and concentration‐related actions of lipopolysaccharide (LPS) on the synthesis of prostaglandin E₂ (PGE₂) were investigated in cartilage explants and synoviocytes harvested from 3 age groups of horses, all with clinically normal joint function: group A <10 years; group B 11–20 years and group C >20 years. Cartilage explants from group A horses were least and those from group C were most sensitive to LPS. Significant increases in PGE₂ concentration (P ≤ 0.01) were obtained in group C horses in response to LPS concentrations of 1.0 μg/mL (and higher) after exposure for 24, 36 and 48 h, whereas explants from group A horses failed to respond to LPS at concentrations up to 100 μg/mL after exposure times up to 48 h. In contrast, synoviocytes from group A horses were most and those from group C horses were least sensitive to LPS stimulation. Synoviocytes from group A horses responded to LPS concentrations of 1 μg/mL (and higher) with significantly increased concentrations of PGE₂ at 24 and 36 h. Significant but numerically smaller increases in PGE₂ concentration were induced by LPS in synoviocytes from groups B and C. As the effects of high PGE₂ concentrations are catabolic for cartilage, these observations suggest that both synoviocytes and chondrocytes might exert roles in the degenerative changes which occur in cartilage in horses with osteoarthritis.     

Effect of dose of furosemide on plasma tCO2 changes in standardbred horses

Nine Standardbred horses of similar athletic fitness (six mares, three geldings), ranging from 4 to 11 years of age, were used to determine the effects of 0, 250, or 500 mg intravenously administered furosemide on plasma tCO₂ changes over time. All horses were either currently racing or in advanced stages of race training before entering a qualifying race. Horses were randomly allotted to one of the three treatment levels of furosemide during 3 consecutive weeks. Jugular venous samples were obtained from horses at rest in box stalls before and hourly for 6 hours after administration of furosemide. Body weights of horses ranged from 356 to 456 kg, and the mean was 417 kg. Thus, the dose of furosemide received by each horse ranged from 0.55 to 0.70 mg/kg body weight for the 250-mg injections and from 1.1 to 1.4 mg/kg body weight for the 500-mg injections. Furosemide caused metabolic alkalosis in the horses. Least square means (±SEM) were determined and horses had adjusted plasma tCO₂ of 32.2, 33.9, and 34.7 ± 0.41 for the 0-, 5-, and 10-mL doses of furosemide, respectively. The type 3 tests of hypotheses found that there was a difference (P < .0001) across time, a difference (P = .0016) according to furosemide dose, and a difference (P < .0001) according to treatment × hour. There was no difference (P > .05) according to week or treatment × week. These data suggest that either 250 or 500 mg furosemide given to Standardbred race horses induces statistically similar metabolic alkalosis.     

Effect of biotin supplementation on the vLa4 of thoroughbred horses

Thoroughbred horses in racing condition were supplemented twice daily with 25 mg biotin (biotin group), while control horses received an equivalent amount of maltodextrose as a placebo (placebo group). Changes of v_fLa4 (running speed necessary for producing a lactate concentration of 4 mmol/l in the blood) were determined with an incremental step test within three days and after two, three and four months after the beginning of supplementation. The mean v_fLa4 of both the biotin and the placebo groups (5 horses each) did not change significantly within three days of supplementation, but the mean plasma biotin concentration increased in the biotin group from 1.3±0.4 to 47±22 nmol/l (p<0.01), while remaining below 3 nmol/1 in the placebo group. There was no significantly different development of the v_fLa4 between groups over four months of supplementation. But, while the mean v_fLa4 of Thoroughbreds supplemented with biotin over this period of time did not show any changes, the v_fLa4 of the placebo group horses showed a tendency to decrease. In the biotin group, the mean plasma biotin levels varied between 38 and 64 nmol/l over the four months, while the biotin concentration of the placebo group never exceeded 3 nmol/1.     

Effects of ozonated autohemotherapy on the antioxidant capacity of Thoroughbred horses

The performance of horses undergoing regular intense exercise is adversely affected by oxidative stress. Thus, it is important to increase antioxidant production in horses in order to reduce oxidative stress. Ozonated autohemotherapy (OAHT) reportedly promotes antioxidant production. This study aimed to evaluate the effects of OAHT on antioxidant capacity. Ten Thoroughbred horses were used in this study. After the OAHT, we collected serum samples and measured biological antioxidant potential (BAP). We found that BAP began to increase after the OAHT and was significantly higher in the OAHT group than at 3 (P<0.01) and 7 days (P<0.05) after OAHT than in the control group at 3 and 7 days after starting collection of blood samples. Therefore, it was shown that OAHT improved the antioxidant capacity of the horses.     

Effect of thyrotropin releasing hormone (TRH) on serum levels of thyroid hormones in thoroughbred mares

Effects of thyrotropin releasing hormone (TRH) on serum levels of thyroid hormones were studied in 12 Thoroughbred mares. Significant increases (P<0.05) of serum T4 levels occurred as early as 2 hours and peaked at 4–10 hours after intravenous injection of 0.5 – 5 mg TRH. Following injection of 0.5, 1, 3 and 5 mg of TRH the serum levels of T4 were increased 2.25, 2.42,2.42 and 3.67 fold, respectively, over pre-injection levels. Serum levels of T3 were also significantly increased (P<0.05) at 1 or 2 hours and peaked at 2 to 4 hoursafter injection. The mean peak increase of T₃ levels were 2.87, 3.21, 3.10 and 3.10 fold over pre- injected in level in 0.5, 1, 3,5 mg treated horses, respectively. These results suggest that TRH can be an alternative to heterologous TSH for the equine thyroid function test. The recommended dosage is 1–3 mg, and most appropriate time to collect post-TRH blood sample is between 4–6 hours. Serum levels of T₄ and T₃ should increase 2–3 fold from baseline in normal horses.     

A study of cardiovascular function under controlled and spontaneous ventilation in isoflurane–medetomidine anaesthetized horses

Objective To determine, in mildly hypercapnic horses under isoflurane–medetomidine balanced anaesthesia, whether there is a difference in cardiovascular function between spontaneous ventilation (SV) and intermittent positive pressure ventilation (IPPV). Study design Prospective randomized clinical study. Animals Sixty horses, undergoing elective surgical procedures under general anaesthesia: ASA classification I or II. Methods Horses were sedated with medetomidine and anaesthesia was induced with ketamine and diazepam. Anaesthesia was maintained with isoflurane and a constant rate infusion of medetomidine. Horses were assigned to either SV or IPPV for the duration of anaesthesia. Horses in group IPPV were maintained mildly hypercapnic (arterial partial pressure of carbon dioxide (PaCO₂) 50–60 mmHg, 6.7–8 kPa). Mean arterial blood pressure (MAP) was maintained above 70 mmHg by an infusion of dobutamine administered to effect. Heart rate (HR), respiratory rate (f_R), arterial blood pressure and inspiratory and expiratory gases were monitored continuously. A bolus of ketamine was administered when horses showed nystagmus. Cardiac output was measured using lithium dilution. Arterial blood‐gas analysis was performed regularly. Recovery time was noted and recovery quality scored. Results There were no differences between groups concerning age, weight, body position during anaesthesia and anaesthetic duration. Respiratory rate was significantly higher in group IPPV. Significantly more horses in group IPPV received supplemental ketamine. There were no other significant differences between groups. All horses recovered from anaesthesia without complications. Conclusions There was no difference in cardiovascular function in horses undergoing elective surgery during isoflurane–medetomidine anaesthesia with SV in comparison with IPPV, provided the horses are maintained slightly hypercapnic. Clinical relevance In horses with health status ASA I and II, cardiovascular function under general anaesthesia is equal with or without IPPV if the PaCO₂ is maintained at 50–60 mmHg.     

Continuous and non-invasive study of brain oxygenation in the calf by near infrared spectroscopy

Near infrared spectroscopy (NIBS) was used to detect changes in brain oxygenation in five tranquilised calves that were placed on a hypoxic gas mixture (10 per cent O₂/90 per cent N₂) and hyperoxic gas mixture (30 per cent O₂/70 per cent N₂) for five minutes at each concentration. A NIRO 500 (Hamamatsu, Japan) was used for the NIBS, with the incident light source and separate detector (optodes) placed on shaved skin on the most dorsal surface of the frontal bone. Sequential arterial blood gas sample analyses provided confirmation of the appropriate change in systemic oxygenation status. By the end of the five-minute-period of breathing 10 per cent oxygen, NIBS of the calf head detected highly significant changes in haemoglobin oxygenation reflective of hypoxaemia, with oxyhaemoglobin decreasing by 23·5 units (P<0·01) and deoxyhaemoglobin increasing by 45·6 units, (P<0·01) from the baseline of breathing room air. Total haemoglobin (oxyhaemoglobin + deoxyhaemoglobin) showed a significant increase of 22·1 units (P<0·05) but there was no significant change in LAIRS determined cytochrome aa₃ oxygenation. Concomitant blood gas alterations included significant decreases in Pa)₂ (−27·8 mmHg, P<0·01), haemoglobin saturation (−29·0 per cent, P<0·05), and PaCO₂ (−7·8 mmHg, P<0·05) and significantly increased blood pH (0·059, P<0·05). At the end of the five minutes of breathing 30 per cent oxygen NIBS of the calf head detected significantly increased oxyhaemoglobin (13·1 units, P<0·01) and decreased deoxyhaemoglobin (−13·7 units, P<0·05) when compared with baseline breathing of room aim. Total haemoglobin and cytochrome aa₃ were unchanged from baseline. The accompanying arterial blood gas changes included significant increases in PaO₂ (30·9 mmHg, P<0·05), arterial O₂ saturation (11·7 per cent, P<0·05), and significantly decreased pH (−0·026, P<0·05), This study showed that NIRS can be used to continuously and non-invasively detect cerebral oxygenation changes in the live calf in response to both increased and decreased systemic arterial oxygen. Additionally, despite induction of profound hypoxaemia, cytochrome aa₃ in the brain did not appear to become reduced.