Effect of a booster vaccination against influenza and equine herpes virus on cardio-respiratory adjustments to strenuous exercise and training in thoroughbred horses.

This study was conducted in order to assess whether exercise- and training-induced cardio-respiratory adjustments are modified during the 10-day period which follows a booster vaccination with an oily adjuvanted inactivated vaccine against influenza and equine herpesvirus-1 (Equiffa). Nine healthy vaccinated thoroughbred horses were used. Six were revaccinated and three were kept as control. All the horses completed a standardised exercise test (SET) that was repeated 4 times, i.e. 10 (SET1) and 2 (SET2) days before revaccination, and 2 (SET3) and 10 (SET4) days after revaccination. During the whole experimental period the horses were trained 6 days per week according to an interval training schedule. Respiratory airflow, tidal volume, respiratory rate and expired minute volume (VE) were measured using a face mask and 2 ultra-sonic pneumotachographs. The oxygen uptake (VO2) and carbon dioxide production (VCO2) were obtained on a breath-by-breath basis, using a mass spectrometer. Heart rate (HR) was continuously measured with a polar horse tester. Venous blood was sampled before and after the test and analysed for biochemical determinations. Blood was also sampled before and 21 days after the booster vaccination for circulating antibody titration. The peak VO2, VCO2, ventilatory equivalent (VE/VO2) and oxygen pulse (VO2/HR) were significantly improved by the 3-week training period. The other cardio-respiratory parameters as well as most of the blood parameters remained unchanged throughout the 4 SETs. The revaccination did not impair any of the parameters measured before, during, or after the SETs. All revaccinated horses showed a rise in antibodies against influenza virus type A1 and A2 and EVH-1 compared to the control horses. It was concluded that, in our horses, revaccination with an oily adjuvanted inactivated vaccine against influenza and EVH-1 did not impair their cardiorespiratory and metabolic adjustments to strenuous exercise and intense training, and that the seroconversion due to revaccination was unaffected by the intense daily exercise experienced by the animals in the post-vaccination period.