Keeping a horse’s immune system strong is crucial to maintain health and good performance. However, for many horses, the demands of training, performance, transport and travelling, weather conditions, parasitic and pathogenic pressure, or even herd dynamics raise the stress level of everyday routines putting the equine’s immune system under pressure. Young horses introduced to training as well as those involved in competitive events appear to be more prone to infections, as there is a relationship between exercise and immune function. Vaccination is optimal to prevent infectious diseases; unfortunately not all vaccines can prevent naturally occurring infections common in horses. Feeding with an eye on immune support can reduce the incidence and severity of infections, resulting in reduced costs connected to veterinary care and failure to perform in competitions and races. The specific beta-glucan structure, beta1,3/1,6-glucan is known for its ability to modulate immune response in human and various animal species, however equine studies with dietary beta-1,3/1,6- glucans are scarce. Recently a long-term study in high performing race horses showed the efficacy and safety of a beta1,3/1,6-glucan as a feed supplement.
Exercise is stress
An association between exercise and immune function has already been recognised for decennia, as it was reported that high performing athletes were more sensitive to upper respiratory tract infections. Exercise can be seen as a kind of stress, which can significantly influence the host’s immune response and, therefore, its susceptibility to infections. Stress hormones such as cortisol and catecholamines are typically released during exercise and have been shown to inhibit the immune response1 . The level and duration of these metabolic and hormonal changes influence the period of immune suppression2 . Also in race horses, it is widely recognised that high performing horses are more sensitive to respiratory infections.
The reason of this increased susceptibility could be related to both their immune status as well as an increased risk of viral exposure to infected individuals3 . In a study, using a treadmill-based exercise protocol, it was shown that ponies subjected to high intensity exercise were susceptible to influenza virus infection while non-exercised controls were protected4 .
Different types of exercise
Despite numerous studies defining the relationship between exercise, the immune response and diseases, the results can be rather contradictory and complex due to the variable nature of the exercise itself, the complexity of the immune system and individual differences.
Factors which are involved are (i) intensity, duration and type of exercise; (ii) acute exercise versus training; (iii) analysed immunological parameters; (iv) timing of measuring immunological parameters after completion of the exercise bout; (v) age, gender, athletic predisposition and breed of the individual animal5,6. It is also very important to distinguish between different types of exercise. Routine training has a beneficial effect on the immune system, wherein more experience and an improved condition of the horse could reduce the level of stress related to exercise. Training can significantly modify both the resting immune function and the response to acute exercise7,8. Whereas untrained horses show immunosuppression after acute exercise and overtraining of horses can result in prolonged suppressive effects.
Horses following an 80 km endurance race showed a prolonged suppression of the immune response that lasts several days post exercise9 . Explanation of the long term suppression of the immune system might be multifactorial, but the endurance horses showed a high serum cortisol response during relative long period of exercise. As transport has been associated with rises in cortisol, transport of horses to and from competitions have to be considered as an additional stress factor. Depending on earlier mentioned multiple factors that influence the stress level of exercise, it is believed that an open window for infectious agents persists for 3-72 hours after exercise.
Study in French trotters
So far, no data is available concerning the influence of oral beta-glucan supplementation in horses. Having seen the effect of exercise on immune function and increased risk for viral exposure on shows and competitions, sport horses are an interesting target group. Recently a double-blind placebo-controlled study was performed to investigate the immune modulating effect of beta-glucan in race horses during the summer competition period. The main objective of the study was to examine the immune response in French trotter horses supplemented with or without high quality beta-glucan* by measuring antibody response against a viral vaccination. Secondly, to verify the safety of prolonged supplementation of beta-glucans in competition horses.
Experimental set up
A total of 32 horses completed the 90 days trial; 16 horses in the control and 16 horses in the beta-glucan group. After 47 days of supplementation, all horses were vaccinated against rabies and received a booster vaccination three weeks later. Vaccination response was evaluated at day 45, 68 and 90. As shown in Figure 1, all horses were sero-negative at day 45. Three weeks after the first vaccination there was a tendency (p=0.1) for higher rabies antibodies response in the group of horses supplemented with beta-glucans. On day 90, mean levels of antibodies were significantly higher for the horses in the treatment group (Figure 1). Other immunological variables as serum IgG levels and different white blood cell counts did not differ between the groups. Other safety variables were examined every 45 days. At day 0, day 45 and day 90, body weight, body condition score, hematobiochemical analysis were performed, individual racing performance and the daily reports of the trainers on any possible adverse effects were checked. No adverse events were observed in any group.