Pulmonary and systemic effects of inhaled endotoxin in control and heaves horses

To investigate whether inhaled endotoxin contributes to airway inflammation and dysfunction in stabled horses, control (n = 6) and asymptomatic heaves (previously termed chronic obstructive pulmonary disease)-susceptible (n = 7) horses were given inhalation challenges with 20, 200 and 2,000 microg of soluble Salmonella typhimurium Ra60 lipopolysaccharide (LPS). LPS inhalation induced a dose-dependent neutrophilic airway inflammatory response in both groups. Inhalation with 2,000 microg of LPS also induced detectable lung dysfunction in the heaves group. LPS inhalation did not alter clinical score, tracheal secretion volume or airway reactivity in either group. The no-response thresholds were lower for the heaves group (<20 microg for airway inflammation; 200 to 2,000 microg for lung dysfunction) than for the control group (20 to 200 microg for airway inflammation; >2,000 microg for lung dysfunction). To enable comparison of these threshold levels with airborne endotoxin concentrations in stables, horses also received a 5 h duration hay/straw challenge, during which the total and respirable airborne endotoxin concentrations were determined. Comparison of the effects of acute LPS inhalation and hay/straw challenges suggest that inhaled endotoxin is not the sole cause of heaves. However, it is likely that it contributes to airway inflammation, both in heaves horses in concert with other inhalants, and in normal horses when they are exposed to high levels in poor stable environments.     

Assessment of copper and zinc status of farm horses and training thoroughbreds in south-east Queensland

The copper and zinc concentrations in the blood of stabled thoroughbred horses and in Australian Stock Horses mares at pasture, either late pregnant or lactating were determined by an atomic absorption spectroscopic method. The plasma concentration of the trace elements in these apparently normal horses were generally below the "normal" range. The plasma copper, caeruloplasmin copper, whole blood copper and plasma zinc concentrations in the stabled thoroughbreds were 0.76 +/- 0.19 micrograms/ml (n = 82), 0.56 +/- 0.14 micrograms/ml (n = 83), 0.75 +/- 0.18 micrograms/ml (n = 82) and 0.47 +/- 0.09 micrograms/ml (n = 83) respectively. The plasma copper and zinc concentrations of all the brood mares at pasture (pregnant and lactating) were 0.56 +/- 0.20 micrograms/ml and 0.47 +/- 0.11 micrograms/ml (n = 30). The plasma copper concentration of the pregnant group of mares (0.64 +/- 0.18 micrograms/ml; (n = 14) was greater than that of the lactating mares (0.49 +/- 0.21; (n = 16). Variation in the plasma copper concentration was also identified between stabled and farm horses, between horses of different stables and between horses of different ages. The proportion of plasma copper bound to caeruloplasmin was 73 +/- 11.8%. These low concentrations of copper and zinc in the plasma of apparently normal horses are of clinical significance since recent evidence has indicated that copper deficiency appears to promote the development of skeletal abnormalities in foals. An alternative to the use of a single plasma sample to identify the copper or zinc deficient horse was discussed.     

Stabling is associated with airway inflammation in young Arabian horses

We examined the effect of stabling on upper and lower airway inflammation in 14 yearling Arabian horses that had been at pasture since birth. Horses were divided into 2 groups of 7. One group was stabled for 3 months and the other remained at pasture. The groups were then switched over for another 3 months. The nasopharynx, guttural pouches and trachea were examined endoscopically and bronchoalveolar lavage performed every month. An upper airway inflammation score was devised based on the magnitude of pharyngeal lymphoid hyperplasia and guttural pouch inflammation. During stabling this score remained constant, whereas it decreased during the 3 months at pasture. Stabling was also associated with a higher number and percentage of neutrophils in bronchoalveolar lavage fluid and with a smaller percentage of lymphocytes. There was no correlation between upper airway inflammation score and bronchoalveolar lavage cytology. During a nasal occlusion test, dorsal displacement of the soft palate occurred more times in stabled than in pastured horses, but this was heavily biased by the results from one animal. We conclude that stabling is associated with inflammation of both the upper and lower airway of young horses.     

Biomarkers of exposure to cyanogens in horses with grass sickness

To test the hypothesis that equine grass sickness may be associated with the ingestion of cyanogenic glycosides from white clover (Trifolium repens), the concentrations of whole blood cyanide, and plasma and urinary thiocyanate, the main metabolite of cyanide, were measured in 12 horses with acute grass sickness and 10 horses with subacute grass sickness, and in 43 control horses, of which 21 were co-grazing with cases of acute grass sickness, 12 grazed pastures where grass sickness had not been reported, and 10 were stabled horses. The healthy horses which grazed with cases of acute grass sickness had higher concentrations of blood cyanide, and plasma and urinary thiocyanate than the other control horses, consistent with an increased exposure to cyanogens. The horses with grass sickness had no evidence of a recent intake of cyanogens, but may have been exposed to increased levels of cyanogens before they became anorexic.     

Investigations of the maintenance system of the Konik Polski horse and its effects on fecal microbiota activity during the winter and summer seasons

Gastrointestinal microbiota play a key role in the nutrients digestion and hence maintaining animal health and welfare. The diet offered to the animals in captivity may differ considerably from that on natural pastures. In a stabled maintenance system, horses have a limited choice of habitat and feed. Time spend for feeding is relevant for equine welfare because the reduction of the time devoted for foraging may be responsible for inducing gastric inflammation and ulceration. Therefore, in the present study, it was hypothesized that fecal bacterial fermentative processes differ between free-roaming and stabled Konik Polski Horses (KPHs) with respect to microbial enzymatic activity, and thus the fecal concentration of short-chain fatty acids (SCFA), which can be further utilized for assessing the feeding behavior and welfare in free-roaming versus stabled horses. The SCFA concentration and profile, as well as the extracellular and intracellular activities of selected bacterial enzymes, were characterized in horse feces collected during the winter and summer feeding seasons. The results showed higher enzymatic activity and SCFA production in the feces excreted by free-roaming versus stabled horses, especially during summer. An increase in pasture plant diversity may be beneficial for the gastrointestinal microbiota and hence for maintaining health and welfare.     

The use of cardboard bedding material as part of an environmental control regime for heaves-affected horses: in vitro assessment of airborne dust and aeroallergen concentration and in vivo effects on lung function

This study aimed to test whether shredded cardboard is an appropriate minimum-dust bedding material for heaves-affected horses. Results of standardized in vitro measurement of airborne dust and aeroallergen concentrations of cardboard bedding were significantly lower than those of common bedding materials. Six heaves-affected horses in clinical remission after pasturing were stabled for two months on cardboard bedding and fed grass silage. Pulmonary function tests (PFT: ventilatory mechanics, arterial blood gases, airway inflammation scoring, bronchoalveolar cytology) were performed before, during and after this period and after stabling the horses in poor hygienic conditions. PFT values measured during and after the stabling period on cardboard bedding were not significantly different from those recorded after the period at pasture or from those of healthy horses, but were significantly different from those recorded in poor hygienic conditions. On basis of the in vitro and in vivo results it can be concluded that cardboard bedding, used in conjunction with low-dust forage, may be appropriate in the provision of minimum-dust management of heaves-affected horses.     

Horses in Switzerland: results of a representative survey of population, housing and use in 2004

A survey of 2559 stables, representative for Switzerland, was conducted in the year 2004, with questions related to age, sex, breed, housing conditions, social contact, use, feeding, ability to move freely on the one hand, and health prophylaxis and health disorders in the past 12 months on the other. With a respond rate of 30.9% to the questionnaire, data for 2912 horses and ponies were recorded. The data were compared to a previous survey of 1997 (Bachmann & Stauffacher, 2002). In this study, data on population, housing and use were analysed. The proportion of horses kept individually, especially in tie-stalls, had substantially decreased since 1997, whereas the proportion of horses living in group housing systems had increased. In 2004, Warmblood and Thoroughbred were kept more often individually than in groups in comparison to other breeds. Swiss Franches-Montagnes horses were kept more often tied up than horses of all other breeds. Access to pasture or paddock was available more often in horses kept in structured group housing systems, but in general more restricted in the winter season. A correlation between use or intensity of use and frequency of pasture/paddock access was not evident. Even though horses older than 20 years were more rarely used or intensively used, they were not stabled differently from younger horses.     

The Use of Cardboard Bedding Material as Part of an Environmental Control Regime for Heaves-affected Horses: In Vitro Assessment of Airborne Dust and Aeroallergen Concentration and In Vivo Effects on Lung Function

This study aimed to test whether shredded cardboard is an appropriate minimum-dust bedding material for heaves-affected horses. Results of standardized in vitro measurement of airborne dust and aeroallergen concentrations of cardboard bedding were significantly lower than those of common bedding materials. Six heaves-affected horses in clinical remission after pasturing were stabled for two months on cardboard bedding and fed grass silage. Pulmonary function tests (PFT: ventilatory mechanics, arterial blood gases, airway inflammation scoring, bronchoalveolar cytology) were performed before, during and after this period and after stabling the horses in poor hygienic conditions. PFT values measured during and after the stabling period on cardboard bedding were not significantly different from those recorded after the period at pasture or from those of healthy horses, but were significantly different from those recorded in poor hygienic conditions. On basis of the in vitro and in vivo results it can be concluded that cardboard bedding, used in conjunction with low-dust forage, may be appropriate in the provision of minimum-dust management of heaves-affected horses.     

Environment and prednisone interactions in the treatment of recurrent airway obstruction (heaves)

Recurrent airway obstruction (RAO) or heaves is a manifestation of a hypersensitivity to dust, moulds, and spores in the environment of a susceptible horse. Although in the majority of RAO-affected horses, clinical remission can be achieved by keeping horses at pasture to reduce their allergen exposure, this often is not practicable. For this reason, we investigated if changing the environment of a single stall in a 4 stall stable was sufficient to improve lung function and reduce inflammation in RAO-affected horses. In addition, we determined if addition of oral prednisone provided additional benefit. Twelve RAO-susceptible horses were stabled, fed hay, and bedded on straw until they developed airway obstruction. At this point, bedding was changed to wood shavings and they were fed a pelleted diet for 2 weeks. Lung function was measured and bronchoalveolar lavage was performed before and 3, 7, and 14 days after environmental modification. In a crossover design, horses were treated for the 14 days with prednisone tablets (2.2 mg/kg bwt, q. 24 h). Horses then returned to pasture for 30 days. Airway obstruction was greatest before environmental modification. Significant improvement in lung function occurred within 3 days of the change in environment and continued to Day 7. Airway function was best after 30 days at pasture. The clinical response achieved by environmental modification was not significantly improved by addition of oral prednisone. The total number of cells, total neutrophils, and percent neutrophils was greatest before environmental modification. In the absence of prednisone, total and percent neutrophils did not decrease until Day 14 and total cell number until 30 days at pasture. In the presence of prednisone, total cells and total and percent neutrophils decreased by Day 3 and again at pasture. The fact that lung function can be improved within 3 days by environmental management alone emphasises the need for allergen reduction as the cornerstone of treatment of RAO. Although prednisone induced a more rapid reduction in airway inflammation, this was not associated with a more rapid improvement in airway function.     

Efficacy of three corticosteroids for the treatment of heaves

This study used a cross-over design to compare the efficacy of 3 corticosteroids for the relief of airway obstruction and inflammation in 9 heaves-affected horses. The severity of airway obstruction and inflammation was quantified by measurement of lung function and by bronchoalveolar lavage fluid (BALF) cytology, respectively. Airway obstruction was induced by stabling the horses and they remained stabled during the 10 day treatment period. Lung function was measured before treatment (baseline), at Days 3, 7, and 10 of treatment, and after 30 days at pasture. BALF cytology was investigated at baseline, Day 10, and at pasture. All 9 horses received the following 4 treatments in random order: no treatment, daily oral prednisone tablets (1 mg/kg), daily i.v. dexamethasone solution (0.1 mg/kg), and i.m. dexamethasone-21-isonicotinate (0.04 mg/kg) every 3 days. When horses received no treatment, lung function did not change significantly during stabling but improved at pasture. In all horses, daily i.v. administration of dexamethasone solution improved lung function within 3 days to levels as good as or better than those measured at pasture. Dexamethasone-21-isonicotinate was rapidly effective in 8 of 9 horses. The other horse did not respond to this drug. Prednisone tablets were without effect on Days 3 and 7 of treatment, but by Day 10, 5 of 9 horses showed some improvement in lung function. Dexamethasone i.v. solution decreased the percent neutrophils in BALF at Day 10. Other treatments had no effect on BALF cytology. These results demonstrate that dexamethasone rapidly relieved airway obstruction in heaves-affected horses. Oral prednisone had inconsistent effects but may be beneficial in some horses after more than a week of treatment.     

Epidemiological survey of Corynebacterium equi infections on five Ontario horse farms.

Corynebacterium equi was cultured from manure or soil on five horse-breeding farms in Ontario at monthly intervals on three occasions during the summer of 1982. The organism was widespread. Contamination by C. equi of the loafing paddock and pasture areas was significantly greater in a farm established 30 years than in two established for four and six years and there was a significant correlation between the C. equi burden in stables, paddocks and pastures and the length of use of the five farms for horses. In all farms, numbers of C. equi in pasture soil exceeded numbers in fresh manure, suggesting that environmental multiplication of the organism might occur. A farm with an endemic C. equi pneumonia problem differed significantly from the other four farms, where disease was not endemic, in the larger number of C. equi isolated in the stable area. By contrast the farm with a C. equi pasture soil burden significantly heavier than on all other farms had no deaths due to C. equi pneumonia. There was a correlation (r = 0.78, p = 0.061) between the number of cases of C. equi pneumonia on the farms and numbers of C. equi in the area of the stables, but not on the paddocks or pastures. About two-thirds of randomly chosen isolates from the farms belonged to the three capsular serotypes most commonly found in pneumonic foals.     

Airway inflammation in Michigan pleasure horses: prevalence and risk factors

REASONS FOR PERFORMING STUDY: Although subclinical airway inflammation is thought to be common in horses, there is little information on its prevalence and none on risk factors. OBJECTIVE: To determine the prevalence and risk factors for an increased number of inflammatory cells and for mucus accumulation in the trachea of pleasure horses. METHODS: Horses (n = 266) in stables (n = 21) in Michigan were examined endoscopically, once in winter and once in summer 2004. Visible tracheal mucoid secretions were graded 0-5 and inflammatory cell numbers counted in a tracheal lavage sample. Information collected about each horse included age, gender, presence of cough, percent time indoors and source of roughage. The repeated measures were analysed by generalised estimating equations and linear mixed models. RESULTS: Horses eating hay, especially from round bales, had the most neutrophils, whereas horses feeding from pasture had the fewest. Being female and being outdoors in winter were associated with increased numbers of inflammatory cells. Older horses had fewer macrophages than young horses. More than 70% of horses had >20% neutrophils in tracheal lavage. Twenty percent of horses had a mucus accumulation score >1; 17% had both a mucus score >1 and >20% neutrophils. The significant risk factors for mucus accumulation >1 were age >15 years, feeding on hay as compared to pasture, and being outdoors for more than 80% time in winter. Even though mucus accumulation score >1 was a risk factor for cough, only half of such horses coughed. Cough and mucus accumulation were associated with increased number of neutrophils. CONCLUSIONS: In comparison to pasture feeding, hay feeding, particularly from round bales, was associated with an increased number of neutrophils in the airway. Being outdoors in winter was associated with increased numbers of inflammatory cells and with mucus accumulation. Because 70% of horses have >20% neutrophils, this value should not be used as the sole indicator of airway inflammation. POTENTIAL RELEVANCE: The study reinforces the importance of hay feeding and older age as risk factors for inflammatory airway disease. Horses that do not have 'heaves' may be best kept indoors when winters are cold.     

Case-control study of early-term abortions (early fetal losses) associated with mare reproductive loss syndrome in central Kentucky

OBJECTIVE: To identify factors associated with abortions during early gestation classified as mare reproductive loss syndrome (MRLS). DESIGN: Case-control study. ANIMALS: 324 broodmares from 43 farms in central Kentucky, including 121 mares from 25 farms that had early-term abortions (ETAs) associated with MRLS (case horses), 120 mares from the same farms but that did not abort, and 83 mares from 18 farms that were not severely Impacted by MRLS. PROCEDURE: Farm managers were interviewed to obtain data on various management practices and environmental exposures for the mares. Data for case and control horses were compared to identify risk factors for mares having MRLS-associated ETAs. RESULTS: Several factors increased the risk of MRLS-associated ETAs, including feeding hay in pasture, greater than usual amounts of white clover in pastures, more eastern tent caterpillars in pastures, abortion during a previous pregnancy, and sighting deer or elk on the premises. CONCLUSIONS AND CLINICAL RELEVANCE: Analysis indicates that certain characteristics of pastures predisposed mares to MRLS-associated ETAs. Methods for limiting exposure to pasture (keeping mares in stalls longer) during environmental conditions similar to those of 2001 (ie, sudden freezing in mid-April following warmer-than-usual springtime temperatures and larger-than-usual numbers of eastern tent caterpillars in and around pastures) should reduce the risk of mares having MRLS-associated ETAs. It was not possible to determine whether exposure to white clover or caterpillars were causal factors for MRLS or were merely indicators of unusual environmental conditions that resulted in exposure of mares to a toxic or infectious agent.     

Particle mapping in stables at an American Thoroughbred racetrack

Reasons for performing study: Airway inflammation and mucus in the trachea are common in racehorses. Fine airborne particles can initiate and coarse particles can worsen airway inflammation in man and in animal models of airway disease. The regional and seasonal distribution of particles of different sizes has never been investigated in American racing stables. Objectives: To determine the regional and seasonal concentration and number of airborne particles of different sizes in racing stables. Methods: Direct reading instruments were used to determine the mass concentration and numbers of particles 3 times daily (early morning, midday and late afternoon) in July, September and November, in 3 different racing stables. Results: Average particle concentrations were lowest in July and highest in September and November. Early morning concentrations were significantly higher than those measured throughout the rest of the day. The completely enclosed stable with little natural ventilation, had significantly higher particulate concentrations than the open‐sided stable. With regard to numbers of particles, those 2–5 µm were greatest in July and least in November; those 0.5–1.0 µm were greatest in September and least in November. Location of stall within stable also affected concentrations and numbers. Conclusions: The concentration and number of particles in sizes known to reach the lower airways varies with stable design/management, time of day, season of year and location of the stall within the stable. Potential relevance: Particle mapping is a useful tool in the identification of stables, season, and location of stalls within stables where horses may be at greater risk of exposure to offending particulates.     

The prevalence of gastric ulceration in racehorses in New Zealand

AIM: To establish the prevalence and factors influencing the prevalence and severity of gastric ulceration in racehorses in New Zealand. METHODS: Horses (n=171) in active training for racing by trainers (n=24) located throughout New Zealand were examined using gastroscopy during 2003 and 2004. Images of the examination were recorded and reviewed, and an ordinal grade based on the severity of gastric ulceration present was assigned, using the grading system proposed by the Equine Gastric Ulcer Council (EGUC). Information about the horses such as age, breed, sex, stabling, time at pasture, pasture quality, and presence of clinical signs consistent with equine gastric ulcer syndrome (EGUS) was recorded. RESULTS: Of the 171 horses in the study, 133 (78%) were Thoroughbreds and 38 (22%) were Standardbreds. Evidence of gastric ulceration was present in 151 (88.3%) of these. Prevalence of ulceration was higher at the lesser curvature (LC) and greater curvature (GC) of the stomach than at the saccus caecus (SC; p<0.01), and ulceration was more severe at the LC than at either the GC (p=0.02) or the SC (p<0.001). The prevalence of ulceration did not differ between the two breeds (p=0.51) or between horses of differing ages (p=0.56). Gastric ulceration was evident in 125/141 (89%) horses kept at pasture for at least 4 h/day, in all 13 (100%) horses kept at pasture full time, and in 16/17 (94%) horses stabled full time. Prevalence and severity of ulceration did not differ between horses stabled full time, kept at pasture for part of the day or kept at pasture full time (p=0.33 and 0.13, respectively), and for horses grazed on pasture severity of ulceration did not vary significantly with the quality of the pasture (p=0.12). Neither prevalence (p=0.26) nor severity (p=0.49) of gastric ulceration varied significantly with duration of training. CONCLUSIONS: The prevalence of gastric ulceration in racehorses in New Zealand is similar to that reported elsewhere for horses in active training for racing. Access to pasture for some or all of the day did not appear to be protective.     

Time-dependent alterations in gene expression of interleukin-8 in the bronchial epithelium of horses with recurrent airway obstruction

OBJECTIVE: To evaluate time-dependent alterations in gene expression of chemokines in bronchial epithelium of recurrent airway obstruction (RAO)-affected horses and whether alterations resulted from increases in gene expression of interleukin (IL)-17 in cells isolated from bronchoalveolar lavage fluid (BALF). ANIMALS: 8 RAO-susceptible horses and 9 control horses. PROCEDURE: In 2 experiments, both groups of horses were evaluated after being maintained on pasture and after being stabled and fed dusty hay for 1, 14, 35, and 49 days (experiment 1) or 14 and 28 days (experiment 2). In experiment 1, gene expression of IL-8, chemokine (C-X-C motif) ligand 1 (CXCL1), granulocyte-macrophage colony-stimulating factor (GM-CSF), granulocyte colony-stimulating factor (G-CSF), and Toll-like receptor 4 (TLR4) in epithelium and IL-8, IL-17, and TLR4 in BALF cells was measured. In experiment 2, bronchial biopsy specimens were evaluated for IL-8 immunoreactivity. RESULTS: In RAO-susceptible horses after 14 days of challenge exposure, there was a 3- and 10-fold increase in gene expression of IL-8 for epithelial and BALF cells and an increase in IL-8 immunoreactivity in epithelial cells. Challenge exposure failed to alter gene expression of CXCL1, GM-CSF, G-CSF, and TLR4 in epithelial cells of any horses at any time point. During challenge exposure, gene expression of BALF cell IL-17 was downregulated in control horses (day 1) and upregulated in RAO-affected horses (day 35). CONCLUSIONS AND CLINICAL RELEVANCE: Epithelial-derived IL-8 may promote airway neutrophilia, but the inciting stimulus is unlikely to be IL-17 because upregulation of this gene is subsequent to that of IL-8 in epithelial cells.     

Relationship of equine housing to large airway inflammation

The pasture, as compared to stall confinement, has been considered a more desirable environment for maintaining the health of the respiratory system in the horse. This conclusion is based on reports which showed that ventilation in most barns was generally poor, and that horses bedded on straw and fed hay were exposed to many forms of respirable debris. In this study, six normal horses were evaluated for evidence of airway mucosal inflammation after being housed on pasture or stabled in a barn for one month. The response of the horses' airways was measured by assigning scores for the degree of tracheal mucosal secretions that were observed by endoscopic visualization. Cytological examination of transtracheal wash secretions was also performed, as well as histologic evaluation of tracheobronchial tissues obtained by a transendoscopic epithelial biopsy technique. Samples were collected at three time points; the initial collection occurred after the horses were housed on pasture for one month. The horses were subsequently moved to a barn for an equal length of time and samples were obtained at the end of this period. The horses were then returned to their original pasture and final sampling was performed after they were housed in this environment for two months. There were no significant changes in any of the parameters evaluated, regardless of the environment in which the horses were maintained. These findings indicate that housing horses in a barn for four weeks does not cause tracheobronchial mucosal inflammation in a manner that could be detected using the methods employed in this study.     

Cortisol Circadian Rhythm Ratio: A Simple Method to Detect Stressed Horses at Higher Risk of Colic?

With the hypothesis that police horses with abnormal cortisol circadian rhythm (CCR) had more chance to develop colic, the aim of this study was to determine the CCR ratio in horses subjected to different housing and work conditions and to associate abnormal CCR ratio with incidence of colic. A total of 116 police horses belonging to four different groups were studied. In all, 31 were full-time stabled and performed urban patrolling activity, 27 were full-time stabled and performed equine therapy and sports activities, 25 were part-time stabled and performed urban patrolling, and 33 animals were kept full-time on pasture and did not perform any kind of work activity. Venous blood samples were collected between 6 and 7 am and also 8 hours later, and cortisol concentrations were determined by radioimmunoassay to calculate the CCR ratio. Annual colic incidences (6 months before and after the day on which CCR ratio was determined) were assessed by examining individual medical files. The overall incidence of abnormal CCR ratio (<0.30) was 63.3%, and 107 cases of colic were reported for this population with a mean incidence of 0.92 colic/horse/yr. Horses with abnormal CCR had 2.3 times more chance to have colic (95% CI: 1.07 to 5.28, P = .03) when compared with those with normal CCR. In conclusion, high incidence of abnormal CCR ratio indicates that police horses were under stressful conditions. Horses with abnormal CCR ratios were more prone to suffer colic episodes, indicating that CCR ratio determination could perhaps be useful in detecting horses at risk of colic.     

Copper and zinc levels in the blood of thoroughbreds in training in the United Kingdom

The concentration of copper and zinc in the blood and sera of over 300 Thoroughbreds in training was determined by atomic absorption between February 1979 and July 1981. The mean (+/- sd) concentration of copper in the serum of stabled Thoroughbreds (79 +/- 16 micrograms/dl) was significantly (P less than 0.0001) lower than that of those at grass (101 +/- 26 micrograms/dl), whereas the mean serum zinc concentration of stabled Thoroughbreds (170 +/- 54 micrograms/dl) was higher than that of those at grass (111 +/- 45 micrograms/dl). No such differences were observed in whole blood. There were marked differences in the mean serum copper and zinc concentrations in the blood of Thoroughbreds housed in different stables. Significant changes occurred throughout the year in the mean values from individual stables. However, there were no such changes in the mean values of the total population. The observed differences were probably caused by dietary variations. The results emphasise the need to establish reference values related to diet if copper and zinc levels in blood are to be used for interpretative purposes.