Rearing sheep, Dad closes in sylvan tract (7)
I believe the answer is:
rampant
'rearing' is the definition.
(I know that rearing can be written as rampant)
'sheep dad closes in sylvan tract' is the wordplay.
'sheep' becomes 'ram' (male sheep).
'dad' becomes 'pa' (both can mean one's father).
'closes in' says to take the final letters (I've seen 'close in' mean this).
The final letters of 'sylvan tract' are 'nt'.
'ram'+'pa'+'nt'='RAMPANT'
(Other definitions for rampant that I've seen before include "Flourishing excessively as disease may be" , "Spreading unchecked" , "Growing or spreading uncontrollably" , "Uncontrolled" , "Unbridled" .)