Food that a racehorse needs (4)
I believe the answer is:
tack
'food' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for tack that I've seen before include "Small broad-headed nail" , "Alter course - riding gear" , "Rubbishy things" , "main course?" , "Small nail with broad head" .)