Prevalence and clinical importance of heart murmurs in racehorses

OBJECTIVE: To determine the prevalence of various types of heart murmurs in Thoroughbred racehorses and assess their association with performance by echocardiography and review of the horses' race records for the preceding 2 years. DESIGN: Clinical and retrospective study. ANIMALS: 846 Thoroughbred racehorses. PROCEDURE: Cardiac auscultations were performed by 3 individuals; for 30 horses, Doppler echocardiographic examinations were also performed. Statistical analyses of race records for 753 horses were performed to assess association of heart murmurs with performance. RESULTS: Heart murmurs were detected by cardiac auscultation in 686 of 846 (81.1%) horses. Systolic murmurs over the heart base were most common; 365 (43.1%) horses had systolic murmurs that were loudest over the pulmonary valve area, and 232 (27.4%) horses had systolic murmurs that were loudest over the aortic valve area. Systolic murmurs over the tricuspid valve area were detected in 241 (28.5%) horses, whereas systolic murmurs over the mitral valve area were detected in only 32 (3.8%) horses. Diastolic murmurs were much less common than systolic murmurs. Review of race records did not reveal a significant association between murmurs and performance. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that heart murmurs are a common finding in racehorses; most of these heart murmurs do not appear to be clinically important.     

Effects of a nine-month endurance training programme on muscle composition in the horse

Muscle biopsy samples were collected from the middle gluteal muscle of seven horses undergoing a nine-month endurance training programme. Samples were collected before the programme began and again after three, six and nine months of training. A fifth sample was collected three months after training ceased. Serial muscle sections were reacted histochemically for myosin adenosine triphosphatase after either acid (pH 4.3 and 4.6) or alkaline (pH 10.3) pre-incubation, and muscle fibres identified as type I, IIA, IIB or IIC. The oxidative capacity of individual fibres was assessed, using the reduced nicotinamide dinucleotide tetrazolium reductase stain, and the number of intermyofibrillar capillaries adjacent to each fibre was counted after staining, using the alpha-amylase periodic acid Schiff technique. Biochemical analyses involved the fluorometric measurement of the enzymes citrate synthase, 3-hydroxy acyl CoA dehydrogenase and lactate dehydrogenase as markers of end terminal oxidative, beta oxidative and glycolytic potential, respectively. There was an increase in the percentage of type IIB fibres having high nicotinamide dinucleotide tetrazolium reductase staining after three months training. This increase persisted throughout the period of training and during the period without training. There was an increase in the number of capillaries adjacent to type IIB fibres after six and nine months training. These had returned to near pre-training numbers after three months without training. There were increases in the activities of citrate synthase and 3-hydroxy acyl CoA dehydrogenase after three months training. The activities of both enzymes continued to rise throughout training and the highest activities were attained after nine months.(ABSTRACT TRUNCATED AT 250 WORDS)     

Microsomal oxidase activity of three blowfly species and its induction by phenobarbital and β-naphtoflavone

Induction of the microsomal oxidase system by dietary phenobarbital and β-naphthoflavone was examined in three blowflies, Phormia regina (Mg.), Lucilia illustris (Mg.), and Eucalliphora lilica (Walk.). Responses were similar in adults and larvae of all species. Phenobarbital increased cytochrome P-450 levels up to 9-fold and aldrin epoxidase up to 138-fold. Increases in cytochrome P-450 and aldrin epoxidase caused by β-naphthoflavone were minor relative to those produced by phenobarbital. In toxicity experiments with carbaryl and propoxur tolerance was associated with the amount of microsomal oxidase activity. Using piperonyl butoxide to synergize carbaryl and propoxur there was no clear indication for the use of either the synergist ratio or synergist difference as an indicator of microsomal oxidase activity.     

Effect of a respiratory gas collection mask on some measurements of cardiovascular and respiratory function in horses exercising on a treadmill

The effects of a respiratory gas collection mask on arterial blood gases, acid base values, oxygen content, respiratory frequency and heart rate, were investigated in standardbred horses during treadmill exercise at speeds up to 10 m sec-1 and a treadmill slope of 10 per cent. The mask had no significant effect on heart rates during exercise, but respiratory frequency was lower when the mask was used. The increase in respiratory frequency as treadmill velocity increased was also significantly slower with the mask operative. Arterial carbon dioxide tensions were significantly higher during exercise with the mask than without, and arterial oxygen tension was significantly lower at the highest exercise intensity. Arterial oxygen content was significantly lower at all work speeds when the mask was used. There were minimal effects of the mask on arterial acid base values. It was concluded that a respiratory gas collection mask caused alveolar hypoventilation in exercising horses, but did not markedly influence heart rate or arterial acid base values during exercise.     

Effects of N,N-dimethylglycine on cardiorespiratory function and lactate production in thoroughbred horses performing incremental treadmill exercise

In a crossover study, either a placebo paste or N,N-dimethylglycine was administered orally at a dose rate of 1.2 mg/kg twice daily for five days to six thoroughbred horses, with bodyweights ranging from 424 to 492 kg. Using previously determined regression equations for oxygen uptake (VO2) against speed for each horse, a standardised exercise test was given with speeds equivalent to fixed percentages of the maximum oxygen uptake (VO2max). The test consisted of two minutes at speeds equivalent to approximately 40 per cent and 50 per cent VO2max, and one minute at speeds that produced approximately 60, 70, 80, 90 and 100 per cent VO2max. During the last five seconds of each exercise stage, the values of VO2, carbon dioxide production (VCO2), heart rate, arterial blood and plasma lactate concentrations, arterial blood gases and pH were measured. Before and immediately after the exercise test, muscle biopsies were collected from the middle gluteal muscle to determine the muscle lactate concentrations. The administration of N,N-dimethylglycine produced no significant differences in any of the measured values, and it is concluded that the compound has no beneficial effects on cardiorespiratory function or lactate production in the exercising horse.     

Effect of mulesing and shearing on the prevalence of effect of mulesing and shearing on the prevalence of Erysipelothrix rhusiopathiae arthritis in lambs

OBJECTIVE: To examine the effects of management practices and environment on the prevalence of arthritis in lambs. DESIGN AND POPULATION: A case-control study was conducted on groups of lambs from 122 Western Australian sheep flocks. METHOD: Arthritis was diagnosed by visual assessment of lambs at abattoirs by qualified meat inspectors. The prevalence was estimated from data collected from producers on culling practices for arthritis. Data on management practices and environmental variables were collected by personal interview. Stepwise logistic regression was used to measure the effects of the most important factors on the prevalence of arthritis. RESULTS: Mulesing and shearing lambs increased the odds of high prevalence of arthritis by 7 (95% CI 1.9 - 25.6) and 4.3 (95% CI 0.9 - 19.6) times, respectively compared to unmarked and unshorn lambs. Lambs slaughtered between December and June had 3.7 (95% CI 0.8 - 16.6) times greater odds of having a high prevalence of arthritis than lambs slaughtered in the remainder of the year. CONCLUSIONS: This study indicates that, to decrease the risk of high prevalence of arthritis, lambs raised for meat production should not be mulesed or shorn. Recommended improvements to hygiene at mulesing such as the use of portable yards had little effect on the prevalence of arthritis.     

PAROXYSMAL ATRIAL FIBRILLATION IN A RACEHORSE

A 4-year-old thoroughbred stallion with a history of loss of racing form was studied over a period of approximately 7 months. At the initial examination he showed positive T waves in 1 chest lead and wandering of the pacemaker. This was followed by an episode of paroxysmal atrial fibrillation which disappeared spontaneously and was replaced by significant T wave changes in all the chest leads. During a period when these changes persisted, there was progressive lengthening of the P wave and the P-R interval. Because the last ECG showed evidence of intra-atrial block, first degree A-V block and T wave changes, the owner was advised that a fluctuating myocarditis was affecting the horse's performance and it was retired to stud. This appears to be the first report of paroxysmal atrial fibrillation in Australia, and it demonstrates the value of regular follow-up examinations in horses with initial electrocardiographs showing only minor departures from normal. The case also suggests that when sharp reversals of racing form occur, the possibility of paroxysmal atrial fibrillation being the cause should be kept in mind.     

A Comparison of Simultaneously Collected Arterial, Mixed Venous, Jugular Venous and Cephalic Venous Blood Samples in the Assessment of Blood-Gas and Acid-Base Status in the Dog

Blood samples were collected simultaneously from the pulmonary artery, jugular vein, cephalic vein, and carotid artery in awake dogs. Blood-gas and acid-base values were measured from these blood samples in normal dogs and in dogs after production of metabolic acidosis and metabolic alkalosis. The values obtained from each of the venous sites were compared with those obtained from arterial blood to determine if venous blood from various sites accurately reflected acid-base balance and could therefore be used in the clinical patient. The results of this study demonstrated significant differences between the blood from various venous sites and the arterial site for PCO2 and pH in all acid-base states. Significant differences for standard bicarbonate (SHCO3) were found only when jugular and cephalic venous blood were compared with arterial blood in dogs with a metabolic acidosis. No significant differences were found for BE when blood from the venous sites was compared with arterial blood. The values for pH, HCO3, TCO2, BE, and SHCO3 measured on blood collected at the various venous sites were found to correlate well with those obtained from arterial blood, with a correlation coefficient of 0.99 for HCO3, TCO2, BE, and SHCO3. These correlation coefficients, together with similar values in BE at all collection sites, indicate that, in the dog with normal circulatory status, blood from any venous site will accurately reflect the acid-base status of the patient.     

Effect of Canine Hyperadrenocorticism on Coagulation Parameters

Background

Hyperadrenocorticism (HAC) has been associated with thrombotic disease in dogs.

Hypothesis

The purpose of this study was to use thromboelastography (TEG) and measurement of thrombin generation (TG) to characterize the hypercoagulable state in dogs with HAC. We hypothesized that dogs with HAC would have a hypercoagulable profile on TEG tracings and an increase in thrombin generation as measured by endogenous thrombin potential (ETP).

Animals

Sixteen dogs with HAC. Dogs were compared with a population of normal dogs used to obtain reference intervals.

Methods

TEG tracings on citrated whole blood were obtained from 15 dogs, and TG measurements on frozen‐thawed platelet‐poor plasma (PPP) were obtained from 15 dogs.

Results

For the TEG analysis, when results of individual dogs were compared with the reference interval, 12/15 dogs had at least 1 parameter associated with hypercoagulability. When the population of HAC dogs was compared with a population of healthy dogs, HAC dogs had decreases in R and K and increases in α and MA values. The ETP was increased when the HAC group was compared with a population of normal dogs. However, only 3/15 dogs had an ETP above reference interval, and 1/15 had a decreased lag time.

Conclusion and Clinical Importance

Of 16 dogs with HAC, 12/15 had evidence of hypercoagulability when evaluated by TEG, 4/15 when evaluated by TG, and 2 dogs had increases in ETP and MA.