The past form of a verb shows an action finished; for example, the past form "wrote" shows the writing process ended. Additionally, the past participle refers to a verb form used as part of perfect tenses. Besides this, in some verbs, the past participle and past form are the same.
In the case of the sentence presented the verb is "lead" and both the past form and past participle of this verb is "led". Besides this, it is appropriate to choose "led" over "lead" because the sentence "The jockey lead the jittery thoroughbred to the starting gate just before the race" suggests the action has finished or it is complete, and therefore a past form should be used.
It demonstrates that you have thoroughly explored the topic, and that you are aware of alternate points of view. By addressing or refuting the counterclaims logically, you gain credibility for your argument.
