Rhodococcus equi infection in foals: the science of 'rattles'.

Infection with Rhodococcus (Corynebacterium) equi is a well-recognised condition in foals that represents a consistent and serious risk worldwide. The condition manifests itself primarily as one of pulmonary abscessation and bronchitis, hence the terminology of 'rattles' derived from its most obvious clinical sign, frequently terminal when first identified. This review addresses the clinical manifestation, bacteriology and pathogenesis of the condition together with recent developments providing knowledge of the organism in terms of virulence, epidemiology, transmission and immune responses. Enhanced understanding of R. equi virulence mechanisms and biology derived from the recently available genome sequence may facilitate the rational development of a vaccine and the improvement of farm management practices used to control R. equi on stud farms in the future. Reliance on vaccines alone, in the absence of management strategies to control the on-farm challenge is likely to be disappointing.

Comparison of concentrations of Rhodococcus equi and virulent R. equi in air of stables and paddocks on horse breeding farms in a temperate climate.

REASONS FOR PERFORMING STUDY: Rhodococcoccus equi is a significant cause of bronchopneumonia in foals worldwide. Infection of the lungs is believed to result from inhalation of virulent R. equi in dust from contaminated environments. A measure of infectious risk in an environment is the level of airborne contamination. OBJECTIVES: To assess and compare the level of airborne virulent R. equi in paddocks and stables. METHODS: Air samples were collected sequentially over the 2003 foaling season from the paddocks and stables on 3 Irish horse breeding farms affected by R. equi pneumonia. Colony blotting and DNA hybridisation techniques allowed quantitation of virulent R. equi. RESULTS: The odds of detecting airborne virulent R. equi in stables were 173 times greater than in paddocks. The median airborne concentration of virulent R. equi was significantly higher (P < 0.001) in stables than in paddocks on all farms. These observations suggested that stables were high-risk areas for infection. CONCLUSIONS AND POTENTIAL RELEVANCE: Our results indicate that contaminated stables are a significant risk factor in the epidemiology of R. equi pneumonia on horse-breeding farms in a temperate climate, such as in Ireland. Management strategies that improve the air hygiene of stables, through better ventilation, use of less fragile bedding material and the use of fogging agents to reduce the airborne concentration of virulent R. equi, may reduce the incidence and severity of R. equi pneumonia on farms.

Effect of intranasal oxygen administration on arterial blood gas and acid base parameters in spontaneously delivered, term induced and induced premature foals.

The effect of intranasal administration of oxygen at a flow rate of 10 litres per minute for 10 minutes, was studied in a total of 19 foals (thoroughbred and pony) aged between 0.5 and 12 hours. Arterial blood samples were collected before and after oxygen administration for the determination of paO2, paCO2, pHa and base excess. The foals were divided into three groups: five spontaneously delivered thoroughbred and pony foals (group 1), seven term induced thoroughbred foals (group 2) and seven induced premature pony foals (group 3). To examine the effect of duration of oxygen administration on blood gas values, three foals aged five to seven days received intranasal oxygen for 40 minutes and serial arterial blood samples were collected. Significant increases in paO2 values were found in group 1 and group 2 foals in response to intranasal oxygen. When the groups were compared, groups 1 and 2 had significantly higher paO2 values than group 3 foals, whether breathing air or oxygen. The duration of administration of intranasal oxygen had no significant effect on blood gas values.

Mammary secretions in normal spontaneous and induced premature parturition in the mare.

Total calcium, total protein, albumin and globulin content were determined in 49 samples of mammary secretions from 37 crossbred and Thoroughbred mares. The mares were divided into three categories: Group 1--post partum samples from spontaneous full term Thoroughbred deliveries (n = 20); Group 2--pre- and post partum samples from spontaneous full term Thoroughbred deliveries (n = 6); Group 3--pre- and post partum samples from induced premature deliveries in crossbred mares (n = 11). Calcium concentrations of the mammary secretions proved useful in predicting full term and also in assessment of the chances of foal survival in prematurely induced parturition. Mean (+/- se) calcium levels in full term mares that foaled spontaneously (Group 1) were 10.6 +/- 2.7 mmol/litre on the day of parturition. However lower values than this did not necessarily mean parturition would not take place. In Group 2 mares, calcium levels were 4.1 +/- 0.8 mmol/litre just before foaling and rose to 9.2 +/- 1.5 mmol/litre within 20 mins of parturition; an increase of 124 per cent. Group 3 mares, induced prematurely, showed poor foal survival if pre-partum calcium levels were less than 3 mmol/litre. Total protein, albumin and globulin concentrations showed a similar trend but the increase just before or during parturition was much less marked.

Intracranial haemorrhage in pre-viable, premature and full term foals.

A neuropathological examination was carried out on the brains of 58 foals. Forty-two were pony foals induced at various periods of gestation from 200 days onwards. Two were pre-viable pony foals delivered by caesarean section and 14 were Thoroughbred foals (one set of twins, two stillborn, five premature, two dysmature, two convulsive and one induced). The only significant pathological change involved intracranial haemorrhage. Subarachnoid haemorrhage occurred in all of 10 pony foals induced before 301 days of gestation and in two pony foals born by caesarean section at 270 and 280 days gestation. Subarachnoid haemorrhage was also present in some pony and Thoroughbred foals born after 301 days gestation; the incidence usually appeared greater in those pony foals which survived for the shortest periods. Haemorrhage also occurred elsewhere in the brains, including the cerebral white matter, the molecular layer of the cerebellum and the medulla, but the intensity could not be related to either length of gestation or duration of survival. No other neuropathological changes were found that could account for the functional state of the animals, whether they were pre-viable, premature, dysmature or convulsive.

Biochemical constituents of cerebrospinal fluid in premature and full term foals.

Total protein content and a variety of enzyme activities and electrolyte values were determined in 73 cerebrospinal fluid (CSF) samples from 66 horses and ponies. The foals (48) were divided into 3 categories-spontaneously delivered normal foals (Group A), full term induced normal foals (Group B) and premature induced non-surviving foals (Group C). CSF samples from a group of 18 normal adults (Group D) were included for comparison. Paired serum and CSF samples were collected on 32 occasions and subjected to similar analyses. CSF sodium and chloride were always higher than serum sodium and chloride; the reverse occurred with potassium. The CSF protein and enzyme levels were always lower than corresponding serum values. The foals had higher total protein and creatine kinase in CSF than the adults, except for Group C (non-survivors) which had significantly lower creatine kinase than either of the other 2 foal groups. Creatine kinase values tended to fall towards adult levels over 40 h post partum. It was also noted that foals with both high total protein and creatine kinase in CSF, compared with adult values, had a better chance of survival than those with high total protein but low creatine kinase.

Maternal and umbilical venous plasma lipid concentrations at delivery in the mare.

The concentrations and fatty acid composition of the plasma free fatty acid, triacylglycerol and phospholipid fractions were determined in maternal and umbilical cord vein blood samples taken at delivery from 17 mares. Maternal and umbilical vein plasma free fatty acid concentrations were of a similar order and a positive correlation was found between the two levels suggesting that the equine placenta is permeable to fatty acid. Substantial amounts of the essential fatty acids and their longer chain derivatives were seen in both umbilical vein plasma free fatty acid and phospholipid fractions supporting this view. Certain long chain polyunsaturated derivatives of the essential fatty acids found in the umbilical venous plasma phospholipid fraction were not seen in the maternal circulating lipids. The precursor fatty acids were readily available to both foetal and placental tissues and therefore must have been elongated and incorporated into phospholipid by either or both. Very small amounts of the essential fatty acids were found in adipose stores in the newborn foal and virtually no fat stores at all in the newborn foal liver.

Studies on equine prematurity 1: Methodology.

This paper describes the general management of mares and foals during the perinatal period and the methodology used in a collaborative research project on equine prematurity. Sixteen mares with dated pregnancies delivered 45 foals over three breeding seasons (1981 to 1983). In the majority, parturition was induced with oxytocin and/or fluprostenol; the remainder were allowed to foal spontaneously. Pre-colostral milk analysis provided a means of assessing the pre-foaling status of the mare. All were observed and monitored before, during and after parturition and the sampling protocol for both mare and newborn foal is discussed in detail. The foals were assessed for their degree of maturity at birth using behavioural, haematological, acid-base status and other criteria; they were then assigned to groups for further study and tests.

Behavior and viability of the premature neonatal foal after induced parturition.

Parturition was induced in 2 groups of mares, less than 300 (n = 49) and 300 to 320 days gestation (n = 31), by the administration of prostaglandin F2 alpha or fluprostenol and oxytocin. Foals were categorized into 4 groups according to their ability to adapt in, and survive, the neonatal period. Group A had no demonstrable coordinating reflexes, were weak from birth, and all died within 90 minutes. Group B had some righting reflexes, but had poor coordination and a weak suck reflex. They showed some improvement for about 2 hours, but all died within 9 hours. Group C foals had a good suck reflex and made attempts to stand. After 24 hours, there was a steady deterioration and death occurred within 48 hours. Group D were initially weak, but showed rapid clinical improvement with good adaptation to the environment and survived for at least 7 days. The overall survival rate for the 80 foals born was only 5%. Most group A foals had gestational ages of less than 300 days, but a few (n = 9) were delivered after 300 days and 2 up to 319 days. The youngest survivor was delivered at 318 days and the 3 other survivors were delivered at 320 days. Aspects of the hazards of prematurely induced parturition were considered to be immaturity and stress of parturition.

Relationship between kennel size and stress in greyhounds transported short distances by air.

Greyhounds are usually transported by air between Ireland and England in wooden kennels similar in size to greyhound racing starting traps. These kennels have been criticised in the belief that their small size leads to unnecessary stress. The present study compared plasma ACTH, cortisol, lactate and non-esterified fatty acid concentrations in 12 greyhounds transported either in the existing wooden kennels or in wider perspex kennels, which were stowed either in the belly hold or in the main cargo hold of jet freighter aircraft. Increased kennel size did not appear to result in decreased stress responses but there was a significantly greater stress response in the dogs kept in the belly hold of the aircraft. Individual variation between dogs was the most significant feature of the study.

A collaborative project in veterinary practice: developing a model of equine prematurity.

The development and design of a project in collaborative research which originated from a problem identified in practice, namely prematurity in the newly born foal, is described here. The project established a model of equine prematurity for the purpose of studying the diagnosis, pathogenesis and treatment of the condition. It involved practitioners and full time research workers in a number of veterinary and medical institutes.