Jumps in the Grand National
This is a biblical reference to the story of Noah and the flood. The sentence is "40 days and nights of the great flood."
16 Fences in the Grand National. Although some are jumped twice, making a race of 30 jumps in total.
16 fillies in the grand national
That probably should read "40 D and N of the GF", in which case the answer is "Forty Days and Nights of the Great Flood".