Bloomer from animal doctor, if only periodically visiting (6)
I believe the answer is:
violet
'bloomer' is the definition.
(I've seen this before)
'animal doctor if only periodically visiting' is the wordplay.
'animal doctor' becomes 'vet' (veterinarian).
'periodically' indicates alternate letters (letters must be selected 'every so often').
'visiting' means one lot of letters goes inside another.
'if'+'only'='ifonly'
The alternate letters of 'ifonly' are 'iol'.
'vet' going around 'iol' is 'VIOLET'.
'from' acts as a link.
(Other definitions for violet that I've seen before include "It nods on Oberon's bank" , "Girl's name - colour" , "Bloomer" , "Five-petalled flower" , "Colour; flower, source of fragrance" .)