A horse is described as First-up when it is having it's first run after a spell. The first-up run does not take into account trial runs where the horse runs in more casual racing conditions against other horses with no betting, recorded handicaps and barrier positions. The spell or time since the horse last officially raced can range from weeks to months. To be classed as a spell the horse has to finish track work and be sent away for a break in the paddock. When a horse has it's first-up run it marks the beginning of a campaign where it will stay in work (running track work) for the duration of time before its next spell.
Horse's vary in their performance for first-up runs. Some horses relish running fresh in their campaign and perform strongly first-up while other horses require several runs to build race fitness before they arrive at peak fitness in their campaign. Changes in horse's Trainer or training style can impact their career first-up performance so punters should be looking out for any news of this nature.