Statistics of In vitro comparison of acyclovir, ganciclovir and cidofovir against equid alphaherpesvirus 3 and evaluation of their efficacy against six field isolates [Comparación in vitro de aciclovir, ganciclovir y cidofovir contra alfa-herpesvirus equino 3 y evaluación de la eficacia de los mismos frente a 6 aislamientos de campo del virus]