Fig. 1. Clinical findings in old and young horses after intranasal infection with EHV-1 Ab4. (a) Respiratory disease score was calculated using individual scores for cough, nasal and ocular discharge. (b) Neurological disease score was determined by using the ataxia grading system established by Mayhew et al. [53,54] and Allen et al. [32]. Data are presented as mean values (±sem). Differences between groups were statistically significant (P=0.0001 respiratory score, P=0.004 neurological score).