Sentence:  I would rather have the horse fit by the week-end preceding the three-day event and then, apart from a good sharp two-furlong <WSD>pipe-opener</WSD> after the dressage test before cross-country day, only do slow but interesting work, if necessary for long periods if the horse has an excitable temperament. 
Meaning of the word marked with <WSD> tags:  A practice event; a warm-up.