A Shetland ram's horns should grow up, out and away from the skull until they begin to spiral back in.
 

These pictures show the horn growth of three
different rams from lamb to maturity. The second ram broke a horn as a lamb which is why one horn is shorter than the other.

Ram's horns thicken as they mature, so it is
important they start out 
set well apart on the head. 
These yearling rams show a big difference
in spacing between their horns. 
The black ram ended up with tight horns  while
the katmoget ram on the left of the picture
still has good horns.

These three yearling rams all ended up with
good horns although the spotted ram's are
close at maturity .
 

This ram's horns failed to rise up
off hishead, were too closely spaced and
did not grow out and away
before the first spiral.  He was butchered.
 

Incurving horns that grow towards the face,
neck or eyes are a disqualifying fault
in Shetlands.
 

Some Shetland ewes are horned. 
Their horns tend to be more feminine and
dainty in appearance. 
They do not spiral.

Polled Shetland rams can be registered,
but should be clean headed with no evidence
of scurs or horn buds.
 A Shetland ram lamb with extremely slow
horn growth is considered horned, not polled.