Queen surrounded by old horses and asses (7)
I believe the answer is:
onagers
'asses' is the definition.
(onager is a kind of ass)
'queen surrounded by old horses' is the wordplay.
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'surrounded by' indicates putting letters inside.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'horses' becomes 'nags' (nag is a kind of horse**).
'o'+'nags'='onags'
'er' inserted into 'onags' is 'ONAGERS'.
'and' is the link.
(Other definitions for onagers that I've seen before include "Asian wild asses" , "wild animals" , "Asiatic wild asses" , "Strange oranges for the wild asses" .)