Exercise and immunity: a review with emphasis on the horse

Immunology of Physical Exercise: Is Equus caballus an Appropriate Animal Model for Human Athletes?

Domestic horses routinely participate in vigorous and various athletic activities. This enables the horse to serve as a model for studying athletic physiology and immunology in other species, including humans. For instance, as a model of physical efforts, such as endurance rides (long-distance running/aerobic exercise) and races (anaerobic exercise), the horse can be useful in evaluating post-exercise response. Currently, there has been significant interest in finding biomarkers, which characterize the advancement of training and adaptation to physical exercise in the horse. The parallels in cellular responses to physical exercises, such as changes in receptor expression and blood cell activity, improve our understanding of the mechanisms involved in the body's response to intense physical activity. This study focuses on the changes in levels of the pro- and anti-inflammatory cytokines and cellular response in the context of post-exercise immune response. Both the direction of changes in cytokine levels and cellular responses of the body, such as proliferation and expression of surface markers on lymphocytes, monocytes and neutrophils, show cross-functional similarities. This review reveals that horses are robust research models for studying the immune response to physical exercise in human athletes.

Role of Enhancing Aerobic Capacity in Countering COVID-19-induced Liver Injury in Elderlies

COVID-19 is still a world disaster; however, its vaccination is globally available. Liver and gastrointestinal disturbances occur in patients infected with COVID-19 at varying incidences. Aging decreases the functions of the liver. Thus, the elderly have a weaker response to the COVID-19 virus. The COVID-19 virus affects the liver directly through direct and indirect mechanisms. It directly affects the renin-angiotensin system or indirectly causes sepsis, uncontrolled immune reactions, drug-related hepatic injury, and cytokine storm. Also, COVID-19 vaccines and anti-drugs have adverse effects on the liver too. Thus, this review explores the effect of enhancing aerobic capacity as a nonpharmacological intervention on decreasing COVID- 19-induced liver injury. Enhancing aerobic capacity decreases COVID-19-induced liver injury through the following: 1) downregulating systemic and tissue ACE/ANG II/AT1R axis, upregulating ACE2/ANG 1-7/Mas axis, and moving the renin-angiotensin system to the direction of the ACE2/ANG (1-7)/Mas axis, 2) Improving mitochondrial function and oxygenation to body and lung tissues, causing a decrease in harmful oxidative reactions, 3) Increasing the processing of accumulated free radicals and inhibiting the acute respiratory distress syndrome, 4) Acting as an antioxidant to protect the liver from oxidative stress, 5) Increasing the effect of antiviral drugs and COVID-19 vaccines, which improves the function of immune biomarkers, decreases the viral load, and increases the body's defense against the virus, 6) Decreasing coagulation abnormalities and thrombosis. In conclusion, enhancing aerobic capacity may be an efficient nonpharmacological intervention to decrease COVID-19-induced liver injury in elderlies and regenerate the liver to its normal status after being infected by the COVID-19 virus. It also helps to strengthen the body's immunity for better effects of both COVID-19 vaccination and drugs.

Comparative transcriptome analysis of unfractionated peripheral blood leukocytes after exercise in human

Exercise has profound but variable effects on the immune system. However, only limited information exists about the changes of exercise-induced gene expression in whole immune cells. The aim of this study is to unravel the potential molecular changes of genes which are related to immunity after exercise. The raw expression data and corresponding clinical of GSE18966 were downloaded from Gene Expression Omnibus database. The differentially expressed genes between control group and treat groups were performed by in-house developed perl scripts. A total of 83 differentially expressed genes (DEGs) (|log2 FC|> 1, FDR < 0.05) were identified between control and treat group 1 (0 h after exercise), 128 DEGs (|log2 FC|> 1, FDR < 0.05) between control and treat group 2 (4 h after exercise), and there was no significant difference between control and treat group 3 (20 h after exercise). Next, we identified 51 overlapping genes between treat group 1 (0 h after exercise) and treat group 2 (4 h after exercise) using Venn analysis. Protein-protein interaction (PPI) network was constructed by Cytoscape 3.7.2, and nine hub genes (S100A12, FCGR3B, FPR1, VNN2, AQP9, MMP9, OSM, NCF4, HP) were identified. Finally, 9 hub genes were identified as the potential biomarkers of exercise using validation set (GSE83578) verification analysis. These hub genes might serve as potential molecular targets of monitoring exercise and training processes in the further.

Changes in novel anti-infalmmatory cytokine concetration in the bood of endurance and race horses at different levels of training

Several anti-inflammatory cytokines have been proposed as markers for exercise monitoring in humans such as the interleukin 1 receptor agonist (IL-ra), or interleukin 13 (IL-13). Equine athletes may be considered a model for human exercise physiology research, however there is a lack of such studies of this species. Thus, we decided to examine the changes of IL-1ra and IL-13 in serum concentration during aerobic (endurance) and anaerobic (race) exercise in horses of different fitness levels in comparison with the well-known anti-inflammatory cytokine interleukin 10 (IL-10). The group of endurance horses (n = 13) consisted of animals competing over 100 (n = 7) and 120 km (n = 6) rides. The group of racehorses (n = 18) consisted of trained (n = 9) and untrained (n = 9) animals. The blood samples were obtained before and after the exercise. The ELISA test was performed to evaluate the changes of IL-1ra, IL-13 and IL-10 during different types of exercise. In endurance horses there was an increase in IL-13 (p = 0.0012) after the 100 km ride and in IL-1ra (p = 0.0411) after the 120 km ride. In race horses there was a higher IL-13 basal serum concentration in the untrained group, as well as a decrease of IL-13 after exercise (p = 0.0188). In trained racehorses there was an increase in IL-1ra (p < 0.0001) and IL-13 after exercise (p = 0.0028). In conclusion, the reaction of IL-1ra and IL-13 to different types of exercise differ from each other. Thus, in future, they may be helpful in monitoring the fitness of horses, however more research is needed.

An integrated intervention combining cognitive-behavioural stress management and progressive muscle relaxation improves immune biomarkers and reduces COVID-19 severity and progression in patients with COVID-19: A randomized control trial

COVID-19 is a world disaster. In response to COVID-19 quarantine, stress, anxiety, and depression may easily develop which negatively affect immunity and decrease the patient's response against the COVID-19 virus. This study investigated the effect of an integrated intervention combining cognitive-behavioural stress management (CBSM) and progressive muscle relaxation (PMRs) on immune biomarkers and disease severity and progression in patients with COVID-19 and the period to which these changes last. Thirty patients with mild or moderate COVID-19 were randomly distributed into intervention and control groups. The intervention group performed an integrated intervention combining CBSM and PMRs. There were three outcome measures including blood immune markers, salivary immunoglobulin A, and Wisconsin scale (WIS). Two-week post-intervention, there were significant differences between groups in the WIS total score, Leucocytes, Lymphocytes, Interleukin-6, and Immunoglobulin-A. While there were non-significant differences between both groups in Interleukin-10 and TNF-α. The significant differences between groups in the WIS total score, Leucocytes, Lymphocytes, Interleukin-6, and Immunoglobulin-A significantly continued 1 week as a follow-up. This study concluded that performing an integrated intervention combining CBSM and PMRs for 2 weeks significantly increases immune biomarkers mainly Leucocytes, Lymphocytes, Interleukin-10, and Interleukin-6 along with S-IgA. Also, this protocol significantly decreases disease severity and associated stress, anxiety, and depression; and enhances the quality of life in patients with COVID-19. The study was retrospectively registered with NCT04998708.

Measuring Biochemical Variables and Serum Amyloid A (SAA) in Working Mules in Central Italy

According to FAO reports, the global mule population counts about 9 million mules. This hybrid cross of a male donkey and a female horse is mainly used for draft purposes because they are thought to be strong and hardy animals. Most consider mules to be less susceptible to disease and fatigue compared to horses. Therefore, the aim of this study was to investigate the effects of fieldwork on biochemical variables and serum amyloid A in working mules. Blood samples were collected from 10 healthy, female, working mules before and after 8 h of fieldwork. According to statistical analysis, a significant influence (p < 0.05) of fieldwork was found on mules’ electrolyte profile with increased levels of sodium, chloride, and calcium, as well as on blood urea nitrogen and creatinine. After a day of fieldwork, serum sodium, chloride, calcium, urea, and creatinine concentrations were increased, supporting decreases in body water and renal blood flow. However, without comparison to a group of mules that were not exercised yet maintained under similar ambient conditions, it is uncertain whether these changes can be attributed to exercise. Further, no change in SAA concentration was found after exercise, indicating that the work performed did not result in systemic inflammation.

Single housing but not changes in group composition causes stress-related immunomodulations in horses

Domestic horses are currently often subject to management practices that can entail social stressors, which in turn can negatively influence immunocompetence and disease susceptibility.

The present study therefore aimed to characterize the number of various blood leukocyte subsets in horses, focusing on two potentially stressful housing environments: changes in group composition and relocation to individual stabling. Immune measurements were conducted before as well as one and eight days after changes were made. They were complemented by an assessment of plasma cortisol concentrations as well as behavioral observations. One and eight days after relocation to single housing, the mean numbers of eosinophils, T helper cells and cytotoxic T cells decreased by up to 31%, 20% and 22% respectively, whereas the mean numbers of neutrophils increased by 25%. In contrast, one and eight days after changes in group composition not only the mean number of neutrophils, but also of monocytes, T helper cells and cytotoxic T cells increased by up to 24%, 17%, 9%, and 15% respectively. In consequence, an increase in the neutrophil-to-lymphocyte ratio indicating stress-induced immune modulation was found after relocation to single housing, but not after changes in group composition. The changes in leukocyte numbers after relocation to single housing were accompanied by a transient increase in cortisol concentrations after one day and the occurrence of disturbed behavior patterns one week after change in housing condition. In contrast, changes in group composition did not result in an increase of cortisol concentrations or in an increase of aggressive interactions. The results strongly indicate that individual stabling is an intense stressor leading to acute and lasting alterations in blood counts of various leukocyte types. The study highlights a probable negative impact of single housing on welfare and health of horses and an advantage of group housing systems in view of immunocompetence.

Effects of branched-chain amino acids on immune status of young racing horses

High-intensity exercise and competition are associated with depressed immune function. Young horses, which participate in high-intensity exercise and competitions, are at increased risk for the development of infectious disease due to depression of immune function. The effects of branched-chain amino acid (BCAA) supplementation on the immune status of young racing horses were evaluated, determining whether BCAA might help to avoid or reduce immune suppression during exercise and competitions. Twenty horses (10 male and 10 female) were treated with BCAA supplementation; another twenty untreated horses (10 male and 10 female) constituted control group. Peripheral blood was collected from each animal and evaluated for lymphocyte subsets, phagocytosis analysis of monocytes and granulocytes, lymphocyte proliferative response, and expression of cytokine-encoding messenger ribonucleic acids (mRNAs). The numbers of CD4⁺, CD8⁺, and major histocompatibility complex (MHC) class II⁺ cells in females of the treated group were significantly higher than those in females of the control group. The lymphocyte proliferative response in female of the treated group also was significantly higher than that in females of the control group. In addition, expression of mRNAs encoding interleukin-1β (IL-1β) and interferon-γ (IFN-γ) in females of the treated group was significantly higher than that in females of the control group. There were no significant differences between males of the treated and control groups. The results of this study indicated the positive effects of BCAA supplementation in counteracting immunosuppression in young female racing horses during and following high-intensity exercise.

The effect of aerobic exercise on immune biomarkers and symptoms severity and progression in patients with COVID-19: A randomized control trial

BACKGROUND

The World Health Organization in March 2020 has announced that COVID-19 is a world pandemic because the number of infected cases increases rapidly. however, there are several available vaccines, their protection is limited to a certain period. Thus, the role of modalities that improve immune functions should be performed to counter COVID-19 viral load and decrease mortality rates.

OBJECTIVE

To investigate the effect of aerobic exercise on immune biomarkers, disease severity, and progression in patients with COVID-19.

DESIGN

A randomized controlled study.

PARTICIPANTS

Thirty patients with COVID-19 participated in this study. Participants' age ranged from 24 to 45 years old. Participants had a mild or moderate COVID-19. Participants were assigned randomly into two groups, exercise and control groups. There were two main dependent variables including blood immune markers and severity of respiratory symptoms.

INTERVENTIONS

All participants performed 2 weeks of moderate-intensity aerobic exercise for 40 min/session, 3 sessions/week. The measurements were performed at baseline, and after 2-weeks.

RESULTS

At baseline measurements, there were non-significant differences between both groups in the Wisconsin scale total score, Leucocytes, Lymphocytes, Interleukin-6, Interleukin-10, Immunoglobulin-A, and TNF-α (P > .05). After the intervention, the Wisconsin scale (patient-oriented illness-specific quality-of-life) total score significantly decreased in the intervention group (P < .05); while, Leucocytes, Lymphocytes, and Immunoglobulin-A significantly increased in the intervention group (P < .05).

CONCLUSION

The current study indicated that 2 weeks of moderate-intensity aerobic exercise decreased the severity and progression of COVID-19 associated disorders and quality of life. Also, a 2-weeks of aerobic exercise positively affected immune function by increasing the amounts of Leucocytes, Lymphocytes, Immunoglobulin A.

Conceptualisation of sustainable consumer behaviour: converging the theory of planned behaviour and consumption cycle

Purpose

This article attempts to explore the theoretical model and structural dimensions of sustainable consumer behaviour to develop a “sustainable consumer behaviour scale” for sustainable electronic products. Further, this study has tried to elaborate sustainable consumer behaviour by considering the complete consumption cycle which includes purchase, usage and disposal of the sustainable electronic products.

Design/methodology/approach

The theory of planned behaviour (TPB) has been employed to understand the multidimensional nature of sustainable consumer behaviour with the help of qualitative and quantitative methods. With the help of a pilot study followed by a main study, a sustainable consumer behaviour scale for sustainable electronic products has been tested and validated for its factor study, reliability, validity and model fit, etc. Moreover, the influence of demographic variables has also been examined with the help of multi-group analysis.

Findings

This study highlights that the perceived control behaviour and subjective norms are the major factors that influence sustainable consumer behaviour. Moreover, the results also indicate that female consumers, mid income consumers, young consumers (age below 30) and consumers who have studied up to senior secondary level are more sustainable.

Research limitations/implications

The results can be used by policymakers and managers to identify and target particular subjective norms and factors impacting perceived control behaviour along with a specific set of demographics to increase sustainability amongst consumers and businesses. The results of the current study can help in increasing the focus of the academic research towards sustainable consumer behaviour. It will also encourage firms to include sustainable electronic products in their product line.

Originality/value

To the best of authors' knowledge, the current article is the first empirical study to develop a sustainable consumer behaviour scale by including all the different stages of the consumption cycle using TPB for sustainable electronic products. Although multiple efforts have been made by researchers to analyse sustainable consumer behaviour, there is a scarcity in literature in which research has been done to analyse sustainable consumer behaviour by considering the whole consumption cycle (purchase, usage and disposal).

Enhancing oxygenation of patients with coronavirus disease 2019: Effects on immunity and other health-related conditions

Coronavirus disease 2019 (COVID-19) distresses the pulmonary system causing acute respiratory distress syndrome, which might lead to death. There is no cure for COVID-19 infection. COVID-19 is a self-limited infection, and the methods that can enhance immunity are strongly required. Enhancing oxygenation is one safe and effective intervention to enhance immunity and pulmonary functions. This review deliberates the probable influences of enhancing oxygenation on immunity and other health-connected conditions in patients with COVID-19. An extensive search was conducted through Web of Science, Scopus, Medline databases, and EBSCO for the influence of enhancing oxygenation on immunity, pulmonary functions, psycho-immune hormones, and COVID-19 risk factors. This search included clinical trials and literature and systematic reviews. This search revealed that enhancing oxygenation has a strong effect on improving immunity and pulmonary functions and psycho-immune hormones. Also, enhancing oxygenation has a self-protective role counter to COVID-19 risk factors. Lastly, this search revealed the recommended safe and effective exercise protocol to enhance oxygenation in patients with COVID-19. Enhancing oxygenation should be involved in managing patients with COVID-19 because of its significant effects on immunity, pulmonary functions, and COVID-19 risk factors. A mild to moderate cycling or walking with 60%-80% Vo2max for 20-60 min performed 2-3 times per week could be a safe and effective aerobic exercise program in patients with COVID-19 to enhance their immunity and pulmonary functions.

The Effect of Physical Training on Peripheral Blood Mononuclear Cell Ex Vivo Proliferation, Differentiation, Activity, and Reactive Oxygen Species Production in Racehorses

Physical activity has an influence on a variety of processes in an athlete's organism including the immune system. Unfortunately, there is a lack of studies regarding racehorse immune cells, especially when the horse model is compared to human exercise physiology. The aim of the study was to determine changes in immune cell proliferation, lymphocyte populations, and monocyte functionality in trained and untrained racehorses after exercise. In this study, field data were collected. The cells from 28 racehorses (14 untrained and 14 well-trained) were collected before and after exercise (800 m at a speed of about 800 m/min) and cultured for 4 days. The expression of CD4, CD8, FoxP3, CD14, MHCII, and CD5 in PBMC, and reactive oxygen species (ROS) production, as well as cell proliferation, were evaluated by flow cytometry. In addition, IL-1β, IL-4, IL-6, IL-10, IL-17, INF-γ, and TNF-α concentrations were evaluated by ELISA. The creation of an anti-inflammatory environment in well-trained horses was confirmed. In contrast, a pro-inflammatory reaction occurred in untrained horses after training. In conclusion, an anti-inflammatory state occurs in well-trained racehorses, which is an adaptational reaction to an increased workload during training.

Immune Response in Young Thoroughbred Racehorses under Training

Simple Summary

Stressful stimuli, both infectious and non-infectious, can modify and trigger an innate immune response and inflammation, via an attempt to restore a homeostatic state. Coping with stressors can be measured by different procedures, including the evaluation of immunological parameters. These are also modulated by exercise, which can be considered stress prototypic in the Thoroughbred racehorse. To evaluate the complex of physiological regulations during the training period, twenty-nine clinically healthy, two-year-old Thoroughbred racehorses were followed during their first 3 months of sprint training. Blood collection was performed at rest, three times until 90 days of training, for testing immunological parameters during incremental sprint training to evaluate its effect on the immunological status of the animals. During the training period, we observed the following: (A) an increase in red blood cell parameters that are crucial for exercise performance adaptation, improving O₂ transport and muscle cell respiration; (B) variations of blood granulocytes; and (C) changes in inflammatory cytokine gene expression. On the basis of clinical and laboratory findings, training exercise probably played a major role in the modulation of the above parameters. These latter changes could be seen as a preparation of the innate immune system to respond quickly and adequately to environmental conditions.

Abstract

Training has a great impact on the physiology of an athlete and, like all stressful stimuli, can trigger an innate immune response and inflammation, which is part of a wider coping strategy of the host to restore homeostasis. The Thoroughbred racehorse is a valid animal model to investigate these changes thanks to its homogeneous training and highly selected genetic background. The aim of this study was to investigate modifications of the innate immune response and inflammation in young untrained Thoroughbred racehorses during the first training season through haematological and molecular investigations. Twenty-nine Thoroughbred racehorses were followed during their incremental 3-month sprint exercise schedule. Blood collection was performed at time 0 (T0; before starting the intense training period), 30 days after T0 (T30), and 90 days after T0 (T90). Haematological parameters (red and white blood cells, haemoglobin, and platelets) were evaluated and haematocrit (HCT), mean corpuscular haemoglobin concentration (MCHC), and red cells width distribution + standard deviation (RDW-SD) were calculated. Moreover, via RT-qPCR, we investigated the expression of, Interleukin 1β (IL-1β), Interleukin 4 (IL-4) Interleukin 6 (IL-6), Interleukin 2 (IL-2), Interleukin 3 (IL-3), Interleukin 5 (IL-5) Interleukin 8 (IL-8), Trasformig Growth Factor β and α (TGF-β), Tumor necrosis factor α (TNF-α), and Interferon γ (IFN-γ)genes. Main corpuscular volume (MCV) showed a significant (p = 0.008) increase at T90. Main corpuscular haemoglobin (MCH) and haemoglobin concentration (MCHC) values were significantly augmented at both T30 (p < 0.001) and T90 (p < 0.001). Basophils were significant increased at T30 (p = 0.02) and eosinophils were significantly increased at T90 (p = 0.03). Significant differences in gene expression were found for all the genes under study, with the exception of IFN-γ and TNF-α. In particular, IL-2 (T30, p = 0.011; T90, p = 0.015), IL-4 (T30, p = 0.009; T90, p < 0.001), and IL-8 (T30, p < 0.001; T90, p < 0.001) genes were significantly upregulated at both T30 and T90 with respect to T0, TGF-β was intensely downregulated at T30 (p < 0.001), IL-5 gene expression was significantly decreased at T90 (p = 0.001), while IL-1β (p = 0.005) and IL-3 (p = 0.001) expression was strongly augmented at the same time. This study highlighted long-term adjustments of O₂ transport capability that can be reasonably traced back to exercise adaptation. Moreover, the observed changes of granulocyte numbers and functions and inflammatory cytokine gene expression confirm a major role of the innate immune system in the response to the complex of stressful stimuli experienced during the training period.

Role of increasing the aerobic capacity on improving the function of immune and respiratory systems in patients with coronavirus (COVID-19): A review

BACKGROUND AND AIMS

COVID-19 is a public world crisis, however, it is a self-limited infection. In COVID-19, the strength of immune and respiratory systems is a critical element. Thus, this review was conducted to demonstrate the short and long term effects of increasing the aerobic capacity on increasing the function and strength of immune and respiratory systems, particularly those essential for overcoming COVID-19 infections and associated disorders.

METHODS

This review was carried out by searching in Web of Science, Scopus, EBSCO, Medline databases. The search was conducted over clinical trials and literature and systematic reviews on the effects of increasing the aerobic capacity on the function and strength of specific immune and respiratory elements essential for overcoming COVID-19 infections.

RESULTS

This review found that increasing the aerobic capacity could produce short-term safe improvements in the function of immune and respiratory systems, particularly those specific for COVID-19 infections. This could be mainly produced through three mechanisms. Firstly, it could improve immunity by increasing the level and function of immune cells and immunoglobulins, regulating CRP levels, and decreasing anxiety and depression. Secondly, it could improve respiratory system functions by acting as an antibiotic, antioxidant, and antimycotic, restoring normal lung tissue elasticity and strength. Lastly, it could act as a protective barrier to decrease COVID-19 risk factors, which helps to decrease the incidence and progression of COVID-19.

CONCLUSION

This review summarizes that increasing the aerobic capacity is recommended because it has potential of improving immune and respiratory functions which would help counter COVID-19.

The relationship between the welfare quality and stress index in working and breeding horses

The aim of this observational study was to investigate if a relationship exists between the calculated overall individual welfare score (as an indicator of the welfare quality) and the neutrophil:lymphocyte (N:L) ratio (as a stress indicator) in working (draught) and reproduction horses (breeding stallions and broodmares), in two different seasons. The welfare of the horses was assessed by a protocol which included health and behavioural parameters. An individual welfare score was computed, the total and differential WBC count was established and the N:L ratio was calculated for each of the 1482 assessed horses. Using all these parameters, comparisons were made between the horse categories (working horses, breeding stallions, broodmares) in two assessment seasons. Finally, the relationship between the individual welfare score and the N:L ratio was studied in light of the significant correlations found. The highest frequency of health problems was recorded in working horses. The human-animal relationship did not present significant differences between the horse categories. The individual welfare scores were significantly lower (P<0.05) in the working than in the breeding animals, in both assessment seasons. The N:L ratio was significantly higher (P<0.05) in the working horses than in those kept for reproduction. The season had no significant influence (P>0.05) on the investigated parameters. All the significant correlations found between the N:L ratio and the individual welfare score were negative. The results obtained indicate poor welfare in the working horses, comparing with the breeding animals. The findings of our study confirmed that the N:L ratio increases in horses with a poor welfare state. The multiple correlations of the N:L ratio with the individual welfare scores of the assessed horses emphasised the efficiency of this parameter in identifying the acute and chronic stress conditions in the living environment of the animals.

Assessing adaptive immune response phenotypes in Australian Holstein-Friesian heifers in a pasture-based production system

The objective of this study was to determine the repeatability of ranking Holstein-Friesian heifers reared in an Australian pasture-based production system for immune responses (IR) when ranking was based on secondary versus tertiary IR. Further objectives were to investigate associations between IR and stress responsiveness, ADG and resistance to internal parasites. A total of 100 heifers were IR phenotyped at 5 to 6 mo of age and again at 12 to 13 mo of age using commercial vaccine antigens to induce measurable IR. Antibody production to tetanus toxoid (TT) was used to assess antibody-mediated IR (AMIR), and delayed-type hypersensitivity reactions to vaccine antigens were used to assess cell-mediated IR (CMIR). Changes in serum cortisol and haptoglobin were used to assess stress responsiveness and fecal egg counts used as a measure of resistance to internal parasites. Based on testing, animals were categorized as either average to above-average (High) or low responders for IR. Secondary and tertiary AMIR were well correlated (r = 0.651, adjusted R(2) = 0.418, P < 0.0001), whereas correlations between secondary and tertiary CMIR were poor (r = 0.078, R(2) = –0.004, P = 0.450). A Cohen kappa (κ) test of agreement was used to test the consistency of ranking of individual animal for IR and, therefore, the ability to consistently identify low immune responder animals within the herd across test periods. The consistency of ranking (High versus low) was moderately high for AMIR (κ = 0.445), poor for CMIR (κ = –0.055), and fair to moderate for combined IR (κ = 0.395). High AMIR phenotype animals had significantly higher serum cortisol concentrations than their low immune responder counterparts (P = 0.045). A similar relationship was observed in heifers categorized for CMIR, with High CMIR responders having higher serum cortisol concentrations than their low responder counterparts (P = 0.008). High AMIR calves had a higher ADG compared with low AMIR calves (0.72 ± 0.02 versus 0.66 ± 0.06 kg/d; P = 0.009). Serum haptoglobin concentrations and worm egg counts were very low and could not be used to investigate associations with immune responsiveness. It is concluded that secondary and tertiary antibody responses to TT were well correlated in the Holstein-Friesian heifers in this study and that by using the testing procedure described here, low antibody responders were able to be consistently identified in the herd.

Effect of training on plasma myeloperoxidase concentrations measured before and following intense exercise in Thoroughbred racehorses

Exercise in horses induces neutrophil degranulation and subsequent increases in plasma myeloperoxidase concentrations (MPO). It is not known whether this response is affected by training or the sampling time in relation to exercise. Our objective was to evaluate plasma MPO concentration at different time points in response to exercise in Thoroughbreds before and following high-intensity training and to evaluate relationships between plasma MPO concentration, physiological measurements and performance. Throughbred racehorses in active training and racing (n=26) performed an exercise test on a high-speed treadmill at least once at the beginning (first three months), middle (second three months) or end (last three months) of a nine month training period with training intensity (number of fast work sessions) collated for each period. Heart rate, speed and distance were recorded and venous blood collected before (T0), during and up to maximal speed (TVmax), 5 min (T5min) and 4 h (T4h) following exercise for measurement of plasma lactate, serum creatine kinase concentration, plasma MPO concentration, white blood count (WBC), neutrophil count (Neut), lymphocyte count and neutrophil percentage (%Neut). WBC increased above T0 values at all sampling points with no training effect. Neut and %Neut increased above T0 values at T4h, while values at TVmax, T5min and T4h increased as training duration increased. Plasma MPO concentration increased above T0 values at all sampling points in response to exercise with all values increasing as training duration increased. Training intensity did not affect any of the measurements, correlations were not identified between any of the biological markers including MPO and physiological and training measurements and no differences were identified between elite versus non-elite horses. It was concluded that plasma MPO concentration is affected by exercise and training duration, and that further investigation of plasma MPO as an assessor of fitness and readiness for competition is warranted.

Plasma β-endorphin, cortisol and immune responses to acute exercise are altered by age and exercise training in horses

REASONS FOR PERFORMING STUDY

Ageing appears to affect immune and neuroendocirne function in horses and response to acute exercise. No studies have examined the combined effects of training and ageing on immune and neuroendocirne function in horses.

HYPOTHESIS

To ascertain whether training and age would affect the plasma beta-endorphin (BE) and cortisol (C) as well as immune function responses to acute exercise in Standardbred mares.

METHODS

Graded exercise tests (GXT) and simulated race tests (SRT) were performed before and after 12 weeks training at 60 % HRmax. BE and C were measured at rest and at 5, 10, 20, 40, 60 and 120 min post GXT. Leucocyte cell number, CD4+ and CD8+ lymphocyte subsets, and mitogen stimulated lymphoproliferative response (LPR), were measured in jugular blood before and after the SRTs.

RESULTS

Cortisol rose by 5 min post GXT in young (Y) and middle-age (MA) mares (P<0.05) and remained elevated until 40 and 60 min post GXT, respectively during both pre- and post training GXT. There was no rise in C in old (0) mares after either GXT (P>0.05). Pretraining BE rose (P<0.05) by 5 min post GXT in all mares. After training, BE was higher in Y and O vs. MA (P<0.05) at 5 min post GXT. Post training BE was higher at 5 min post GXT in Y and O vs. pretraining (P<0.05). After SRT, lymphocyte number rose in all mares (P<0.05); however, lower lymphocyte numbers (P<0.05) were seen in MA vs. Y and O vs. MA (P<0.05). The O had reduced LPR to Con A and PHA stimulation (P<0.05) compared to Y and MA after the SRT after both pre- and post training SRT. LPR to PWM was lower (P<0.05) in O vs. Y and MA after the pretraining SRT. Training caused an increase in resting LPR to PWM in MA only (P<0.05).

CONCLUSION

Both age and training altered the plasma beta-endorphin and cortisol responses as well as and immune responses to acute exercise.

POTENTIAL RELEVANCE

This study provides important information on the effects of ageing and training that will aid in the management and care of an increasing number of active older horses.

Plasma glutamine concentrations in the horse following feeding and oral glutamine supplementation

REASONS FOR PERFORMING STUDY

Pharmacological benefits of glutamine supplementation have been shown in athletically and clinically stressed human subjects. In the horse, infection and intense exercise have also been shown to significantly decrease plasma glutamine concentrations, but little is known on how best to supplement.

OBJECTIVE

To evaluate whether ingestion of different foodstuffs, with or without L-glutamine (G) or a peptide (Pep) containing 31.5% w/w G in a water-stable form, could affect plasma glutamine concentrations (P-GC).

MATERIALS AND METHODS

Nine feeds (molassed sugar beet-pulp (mSB); naked oats (nO); commercial mix (CM); mSB with 30 or 60 mg/kg bwt G or the G-molar equivalent of Pep; and CM with 60 mg/kg bwt G or equivalent Pep) were offered to 6 healthy mature horses on different days following overnight food restriction. The changes in P-GC were monitored for 8 h post feeding.

RESULTS

After 1.5 h mean +/- s.d. AP-GC were -0.9 +/- 10.2% (mSB), +12.5 +/- 7.1% (nO) and +44.7 +/- 15.9% (CM; P<0.05). deltaP-GC with mSB supplemented with G was +60.9 +/- 30.0% (30 mg; P<0.05) and +156.8 +/- 34.6% (60 mg; P<0.05) at 1 h; deltaP-GC with Pep was 51.0 +/- 31.0% (30 mg equivalent, P<0.05) and +91.1 +/- 9.5% (60 mg equivalent, P<0.05) at 1 h. After 10 days of supplementation with 60 mg/kg bwt G, AP-GC following a further 60 mg/kg bwt G challenge showed a similar increase at 1 h of +154.3 +/- 37.9%; prevalues were unchanged. G and Pep added to CM, increased P-GC by 246.3 +/- 55.3 (+99.2%) and 252.3 +/- 94.2 micromol/l (96.7%) at 1.5 h with concentrations still above prevalues at 8 h (P<0.05). Apart from the CM (with or without supplement), pre P-GC was always regained by 4 h. Plasma NH3 and plasma protein concentrations were unaffected by supplementation with G or Pep.

CONCLUSION

P-GC may be modified by appropriate supplementation with no apparent adverse effects.

POTENTIAL RELEVANCE

Increasing P-GC through appropriate supplementation may be of benefit in the athletically or clinically stressed horse with lowered plasma glutamine concentrations.

Hypogammaglobulinemia in racing Alaskan sled dogs

BACKGROUND

Serum immunoglobulin dynamics have not been studied in racing sled dogs, despite hypoglobulinemia having been reported during racing events.

HYPOTHESIS/OBJECTIVES

Hypoglobulinemia in racing sled dogs is associated with decreases in serum IgA, IgE, IgG, and IgM concentrations during prolonged exercise.

ANIMALS

One hundred and fifty-seven Alaskan sled dogs that successfully completed a 1,000 mile race.

METHODS

Serum was obtained from 118 sled dogs within 1 month before the race and within 12 hours after completing the race. Serum also was obtained after 4 months of rest from 51 dogs that successfully completed the race, including 12 previously sampled dogs. Serum total protein ([TP]), albumin, and globulin ([Gl]) were measured, and serum IgA, IgE, IgG, and IgM were quantified by ELISA.

RESULTS

The proportion of dogs with [Gl] < or = 2.2 g/dL was significantly greater immediately after racing (38 of 118 dogs, 32.2%) than before racing (21 of 118 dogs, 17.8%, P = .005). Four months after racing, [Gl] was < or = 2.2 g/dL in 23.5% (12 of 51) of dogs. [IgG] was significantly lower before (8.21 +/- 4.95 mg/mL) and immediately after (7.97 +/- 5.62) racing compared with 4 months after racing (18.88 +/- 5.76). Serum [IgM] and [IgE] were higher and [IgA] was lower before racing compared with immediately after racing.

CONCLUSIONS AND CLINICAL IMPORTANCE

Sled dogs participating in long-distance racing have substantial decreases in [IgG] in addition to decreases in [IgM] and [IgE]. The pronounced hypogammaglobulinemia observed in a large proportion of racing sled dogs might predispose them to infectious disease.

Bee pollen product supplementation to horses in training seems to improve feed intake: a pilot study

The objective of this study was to determine the efficacy of supplementation of Dynamic Trio 50/50, a bee pollen-based product, to improve physical fitness, blood leukocyte profiles, and nutritional variables in exercised horses. Ten Arabian horses underwent a standardised exercise test (SET), then were pair-matched by sex and fitness and randomly assigned to BP (receiving 118 g of Dynamic Trio 50/50 daily) or CO (receiving 73 g of a placebo) for a period of 42 days. A total collection was conducted from days 18 to 21 on six geldings to determine nutrient retention and neutral detergent fibre (NDF) and acid detergent fibre (ADF) digestibility. Horses were exercise conditioned and completed another SET on day 42. V160 and V200 were calculated from SET heart rates (HR). Lactate, glucose, haematocrit (HT) and haemoglobin (HB) concentrations were determined from SET blood samples. Total leukocyte count, and circulating numbers of various leukocytes and IgG, IgM and IgA concentrations were determined in rest and recovery blood samples from both SETs. Geldings on BP (n = 3) ate more feed than CO. BP had less phosphorus excretion, and tended to retain more nitrogen. BP tended to digest more NDF and ADF while having lower NDF digestibility and tending to have lower ADF digestibility. No treatment differences existed for V160 and V200, HR, lactate, HT and HB. There was a trend for lymphocyte counts to be lower in BP than CO on day 42. Dynamic Trio 50/50 supplementation may have a positive effect on performance by helping horses in training meet their potentially increased nutrient demands by increasing feed intake and thus nutrient retention.

Effect of submaximal exercise on horse homocysteinaemia: possible implications for immune cells

Physical exercise induces a reduction of immune defences and an imbalance of red-ox status. In this study plasma levels of cysteine and homocysteine (Hcy) were determined in horses before and after submaximal treadmill exercise as well as the effect on horse lymphocyte proliferation. The exercise induced a significant increase in plasma Hcy levels, which remained high both after the 20 min recovery period and after 2 h of rest. Moreover, a reduction of lymphocyte responsiveness to the proliferative stimulus induced by Concanavalin A was observed. The effects of different Hcy concentrations on the proliferative capacity of lymphocytes in culture were also tested. The results indicated that 10 microM of this amino acid can reduce the proliferative capacity of resting lymphocytes as well as their responsiveness to mitogen. Moreover, our results suggest that homocysteinaemia could be considered one of the parameters affected by physical exercise in horses and that this amino acid could be implicated in the effects of physical exercise on the immune system.

Hormesis: the dose-response revolution

Hormesis, a dose-response relationship phenomenon characterized by low-dose stimulation and high-dose inhibition, has been frequently observed in properly designed studies and is broadly generalizable as being independent of chemical/physical agent, biological model, and endpoint measured. This under-recognized and -appreciated concept has the potential to profoundly change toxicology and its related disciplines with respect to study design, animal model selection, endpoint selection, risk assessment methods, and numerous other aspects, including chemotherapeutics. This article indicates that as a result of hormesis, fundamental changes in the concept and conduct of toxicology and risk assessment should be made, including (a) the definition of toxicology, (b) the process of hazard (e.g., including study design, selection of biological model, dose number and distribution, endpoint measured, and temporal sequence) and risk assessment [e.g., concept of NOAEL (no observed adverse effect level), low dose modeling, recognition of beneficial as well as harmful responses] for all agents, and (c) the harmonization of cancer and noncancer risk assessment.

Effects on plasma endotoxin and eicosanoid concentrations and serum cytokine activities in horses competing in a 48-, 83-, or 159-km endurance ride under similar terrain and weather conditions

OBJECTIVE

To determine plasma endotoxin concentration in horses competing in a 48-, 83-, or 159-km endurance race and its importance with regard to physical, hematologic, or serum and plasma biochemical variables.

ANIMAL

3 horses.

PROCEDURE

Weight and rectal temperature measurements and blood samples were obtained before, during, and after exercise. Blood samples were analyzed for plasma endotoxin concentration; serum antiendotoxin antibody titers; thromboxane B2 (TxB2) and 6-keto-prostaglandin F1alpha (PGF1alpha) concentrations; tumor necrosis factor alpha (TNFalpha) and interleukin-6 (IL-6) activities; WBC, plasma protein, lactate, serum electrolyte, and calcium concentrations; PCV; and creatine kinase activity.

RESULTS

Detection of plasma endotoxin increased during exercise for horses competing at all distances but occurred more frequently in the 48- and 83-km groups. Plasma lactate concentration was significantly greater when endotoxin was concurrently detected. Endotoxin in plasma was not significantly associated with success of race completion. Plasma TxB2 and PGF1alpha concentrations and serum IL-6 activity significantly increased with exercise. Horses that had an excellent fitness level (as perceived by their owners) had greater decreases in serum antiendotoxin antibody titers during exercise than did horses perceived as less fit. In horses with better finish times, TxB2 and PGF1alpha concentrations were significantly greater and TNFalpha activity was significantly less than that of slower horses.

CONCLUSIONS AND CLINICAL RELEVANCE

Endotoxemia developed during endurance racing, but was significantly correlated with increased plasma lactate concentration and not with other variables indicative of endotoxemia. Plasma TxB2 and PGF1alpha concentrations and serum TNFalpha activity may be associated with performance success.

Does training affect mRNA transciption for cytokine production in circulating leucocytes?

Physical exertion is a stimulus for the upregulation of cytokine production including IL-1beta, IL-1ra, IL-2, IL-4, IL-6, IL-10 and TNF-alpha in horses. To investigate that hypothesis, we initiated training of 5 stall-rested Thoroughbreds. Blood samples were drawn before and weekly during training. The relative transcription of mRNA within the leucocytes was measured using real time TaqMan quantitative PCR. The training protocol was walking (3 min), trotting (3 min) and cantering/galloping (6 min) increasing in intensity weekly (6 to 12 m/s) and culminating in an intense exercise period. Comparisons of mRNA concentrations were made using a repeated measures ANOVA on ranks and a Student-Newman-Keuls pair-wise multiple comparison (P<0.05). The training programme or intense exercise bout did not affect IL-2, IL-4, IL-6 and IL-10. IL1-beta and TNF-alpha transcription increased on Day 23. TNF-alpha peaked on Day 23 and IL1-beta on Day 30. Neither demonstrated a response to intense exercise. IL-1ra decreased significantly on Day 9; rose significantly from Day 9 to Days 16 and 23; remained significantly elevated through Days 30 and 37 over Day 9, and rose very slightly after intense exercise on Day 56. Alterations in leukocyte cytokine responses may influence susceptibility to infectious disease, metabolic responses to exercise or exercised induced syndromes.

Effects of racing on lymphocyte proliferation in horses

OBJECTIVE

To measure the lymphocyte proliferation response in horses 12 to 16 hours after completion of a race.

ANIMALS

8 Thoroughbreds that competed in 14 races and 3 control Thoroughbreds that did not race.

PROCEDURE

Horses participated in races during the late afternoon or evening. Venous blood samples were collected on a morning before a race (1 or 2 days before the race or on the day of the race), on the afternoon of a race (40 to 60 minutes after the race), and on the morning of the day after a race (12 to 16 hours after the race). Lymphocyte proliferation responses and WBC count were measured in samples obtained in the mornings. Plasma cortisol was measured in all samples.

RESULTS

Lymphocyte proliferation responses were significantly reduced and WBC counts significantly increased 12 to 16 hours after a race. Plasma cortisol concentrations were significantly increased 40 to 60 minutes after a race. In samples from the control horses, lymphocyte proliferation responses, WBC counts, or plasma cortisol concentrations did not differ significantly among time periods.

CONCLUSIONS AND CLINICAL RELEVANCE

A decrease in proliferative responses of circulating lymphocytes can be found as late as 12 to 16 hours after a horse participates in a race. Although the clinical consequences of these exercise-related alterations of the immune response are not yet known, managers of horses should take into account that the immune system of a horse may be affected by racing.

Neutrophil functions and serum IgG in growing foals

The aim of this study was to investigate the phagocytic and killing capacities as well as expression of CD18 of neutrophils obtained from healthy foals from birth to age 8 months. Blood was taken from 6 Standardbred foals at 7 time-points between ages 2-56 days and thereafter once a month. For comparison, cells from 16 mature horses were evaluated. Neutrophil phagocytosis of yeast cells was assessed by flow cytometry after opsonisation with mature pooled serum, autologous serum or anti-yeast IgG. The killing capacity of the neutrophils, as indicated by the oxidative burst, was monitored by chemiluminescence. Serum IgG concentration was measured by radial immunodiffusion. In addition to clinical examination, the amount of serum amyloid A and the total leucocyte count were used as markers for infection. The phagocytic ability was impaired until age 3 weeks, when autologous serum was used as opsonin. Killing capacity was also low initially but, from 3 months onwards, chemiluminescence values were equal to or higher than in mature horses. Serum IgG decreased from 10 g/l at 2 days to 5 g/l at 2 months and then increased gradually to 10 g/l at the end of the study. These findings may in part explain the increased susceptibility to bacterial infections in young horses.

U-shaped dose-responses in biology, toxicology, and public health

The occurrence of U-shaped dose-response relationships (often termed hormesis) has been documented in numerous biological, toxicological, and pharmacological investigations. Many of the endpoints studied are of considerable significance to public health (e.g. body weight, cholesterol levels, ethanol consumption, longevity, cancer incidence, etc). Despite the fact that U-shaped dose-responses are widely and independently observed, little attempt has been made to assess this phenomenon in an integrative manner. This review provides an overview of the historical foundations of hormesis and a discussion of its definition within a mechanistic framework. The occurrence, generalizability, and biological significance of U-shaped dose-response relationships along with the concept of biological optimality are addressed.

Analysis of risk factors for the development of equine protozoal myeloencephalitis in horses

OBJECTIVE

To investigate risk factors for development of equine protozoal myeloencephalitis (EPM) in horses.

DESIGN

Case-control study.

ANIMALS

251 horses admitted to The Ohio State University Veterinary Teaching Hospital from 1992 to 1995.

PROCEDURE

On the basis of clinical signs of neurologic disease and detection of antibody to Sarcocystis neurona or S neurona DNA in cerebrospinal fluid, a diagnosis of EPM was made for 251 horses. Two contemporaneous series of control horses were selected from horses admitted to the hospital. One control series (n = 225) consisted of horses with diseases of the neurologic system other than EPM (neurologic control horses), and the other consisted of 251 horses admitted for reasons other than nervous system diseases (nonneurologic control horses). Data were obtained from hospital records and telephone conversations. Risk factors associated with disease status were analyzed, using multivariable logistic regression.

RESULTS

Horses ranged from 1 day to 30 years old (mean +/- SD, 5.7 +/- 5.2 years). Risk factors associated with an increased risk of developing EPM included age, season of admission, prior diagnosis of EPM on the premises, opossums on premises, health events prior to admission, and racing or showing as a primary use. Factors associated with a reduced risk of developing EPM included protection of feed from wildlife and proximity of a creek or river to the premises where the horse resided.

CONCLUSIONS AND CLINICAL RELEVANCE

Development of EPM was associated with a number of management-related factors that can be altered to decrease the risk for the disease.

Evaluation of risk factors associated with clinical improvement and survival of horses with equine protozoal myeloencephalitis

OBJECTIVE

To investigate risk factors for use in predicting clinical improvement and survival of horses with equine protozoal myeloencephalitis (EPM).

DESIGN

Longitudinal epidemiologic study.

ANIMALS

251 horses with EPM.

PROCEDURE

Between 1992 and 1995, 251 horses with EPM were admitted to our facility. A diagnosis of EPM was made on the basis of neurologic abnormalities and detection of antibody to Sarcocystis neurona or S neurona DNA in CSF. Data were obtained from hospital records and through telephone follow-up interviews. Factors associated with clinical improvement and survival were analyzed, using multivariable logistic regression.

RESULTS

The likelihood of clinical improvement after diagnosis of EPM was lower in horses used for breeding and pleasure activities. Treatment for EPM increased the probability that a horse would have clinical improvement. The likelihood of survival among horses with EPM was lower among horses with more severe clinical signs and higher among horses that improved after EPM was diagnosed.

CONCLUSIONS AND CLINICAL RELEVANCE

Treatment of horses with EPM is indicated in most situations; however, severity of clinical signs should be taken into consideration when making treatment decisions. Response to treatment is an important indicator of survival.

Effects of pulmonary abscesses on racing performance of horses treated at referral veterinary medical teaching hospitals: 45 cases (1985-1997)

OBJECTIVE

To determine whether results of physical or radiographic examination or biochemical analyses in adult racehorses with primary lung abscesses were associated with ability to race following treatment.

DESIGN

Multiple-center retrospective study.

ANIMALS

25 Standardbreds and 20 Thoroughbreds.

PROCEDURE

Medical records of horses with a primary lung abscess that were admitted to any of 4 veterinary teaching hospitals were reviewed. Results of physical examination, laboratory testing, and thoracic radiography were reviewed. Racing performance after treatment was compared with performance before illness and with performance of the general population of racehorses of similar age, sex, and breed.

RESULTS

23 of 25 Standardbreds and 13 of 20 Thoroughbreds raced after diagnosis and treatment of a lung abscess. Most horses had a solitary abscess in the dorsal to caudodorsal lung fields. Results of initial physical examination, biochemical analyses, and culture and identification of the microbial isolate were not associated with whether a horse returned to racing. For horses that had raced prior to the illness, race performance after treatment of the lung abscess was not significantly different from performance before the illness.

CONCLUSIONS AND CLINICAL RELEVANCE

On the basis of racing performance in those horses that resumed racing after treatment, long-term residual lung damage did not develop in horses with primary lung abscesses that were treated appropriately. It is not known whether horses that recovered would be more likely to bleed from the site of a prior infection when resuming strenuous exercise and whether lung abscesses contributed to a failure to resume racing.

Effect of single bouts of moderate and high intensity exercise and training on equine peripheral blood neutrophil function

The effects of single bouts of moderate (30 to 40 per cent VO(2)max) and high (115 per cent VO(2)max) intensity exercise on equine peripheral blood leucocyte function were evaluated by determining neutrophil phagocytosis and oxidative burst activity before and after treadmill exercise and training. Prior to all exercise tests, the possible effect of diurnal variation was evaluated in samples obtained from four resting horses. Subsequently eight horses underwent moderate and high intensity exercise protocols and then commenced a 17-week training period. High intensity exercise tests were repeated in week 10, after 7 weeks of endurance training, and in week 17, after a further 6 weeks of high intensity training. Time of sampling had a significant effect on neutrophil function for resting, untrained horses. Prior to training, moderate intensity exercise was associated with improved neutrophil phagocytosis and oxidative burst activity. High intensity exercise was associated with transient impairment of these responses. A similar reduction was not demonstrable following high intensity exercise in weeks 10 or 17 of training. Neutrophil function in week 17 was suppressed at all sampling times relative to results obtained in week 10, suggesting that high intensity training may have been associated with a general reduction in neutrophil function.

Equine vaccination

Equine infectious disease remains a constant and important threat to the health of domesticated horses. Vaccination plays a critical role in protecting against such disease, but at the present time the efficacy of some equine vaccination strategies is in doubt. The best strategy for resolving these concerns is an improved knowledge of the immunologic basis of successful vaccination, combined with the appropriate integration of effective vaccines into well-designed disease control policies.

Effect of moderate exercise on the severity of clinical signs associated with influenza virus infection in horses

The purpose of this experiment was to determine if exercising horses, infected with influenza virus, exacerbates the severity of clinical disease. Eight horses were trained on a treadmill for 42 days and then challenged with aerosolised influenza A/equine/Kentucky/91 (H3N8). Following challenge, 4 horses (exercise group) continued training for 28 days, while the other 4 horses (nonexercise group) were confined to their stalls. All horses developed clinical signs within 36 h of challenge (fever, coughing, and mucopurulent nasal discharge) and clinical scores were greater in the exercise group. Horses developed fever from Days 1-11 post challenge (PC) and were tachypnoeic and tachycardic from Days 1-14 PC. All horses lost weight within 4 days PC, but the exercise group lost an average of 20 kg more than the nonexercise group. All horses developed pneumonia, and ultrasonography revealed pulmonary consolidation and oedema by Day 7 PC that was resolving by Day 14 PC. Endoscopy and transtracheal aspirates showed airway inflammation for up to 21 days PC. While the exercise group exhibited more severe signs of clinical disease, resolution occurred for both groups on approximately Day 14 PC, and no adverse effects were noted at the end of the study. However, the potential long term effects of exercising horses acutely infected with influenza virus are unknown. Until further research is conducted in this area, it appears prudent not to exercise affected horses.