oats - the most common cereal grain fed to equines

obedient horse - a manageable horse that willingly complies

occult - hidden

ocular - pertaining to the eyes

off side - the right side of a horse

official blueprint - the breed standard

offspring - product of an equine sire and dam

OLWS - initialism for overo lethal white syndrome

omission - to omit

on the market - put up for sale

online auction house - an online wholesaling agent that brings horse purchasers and sellers together

olfactory - related to sense of smell

on the bandwagon - slang for an individual who is unable to make up their own mind

one-trick pony - slang for an individual with training or expertise in one particular area only

open - not pregnant

open show - horse show open to the general public and horses of any age or sex

open stud book - a registry who accepts horses whose sire and dam are not registered in it

open wound - injury in which the skin is cut

opinion - a legal decision

opisthotonus - an arching position of the head caused by brain disease or poisoning

opioid - narcotic drug

opportunistic - disease that is only infectious to horses with reduced resistance

opportunists - individuals who ignore ethics and use circumstances to meet particular goals

opportunity -a favorable and timely circumstance

orally - by mouth

ordinances - laws enacted by local government

.org - the end of a public organization web address

organ - different tissues working together for a common task

organ affected - the primary body part affected by disease

organism - any living thing

Orwellian - term used by some to describe an overpowering government

osteopetrosis - increased bone brittleness

osteoporosis - weakening of the bone

osteomyelitis - bone marrow inflammation

out of - referring to the dam

outbreak - the sudden expension of a disease

outbreeding - mating unrelated horses

outside mare - a mare visiting a farm for breeding purposes that is not owned by the breeding farm

over at the knee - when a horse naturally stands with its front legs bent somewhat forward at the knee

overo - a general term used to describe any pinto spotting pattern other than tobiano

overo lethal white syndrome - lethal recessive genetic disorder causing intestinal abnormalities & death

overshot - when the upper teeth extend beyond the lower teeth

ovulate - when a mature egg is released

ownership - to be owned by or belong to

oxymoron - contradictory phrase such as 'synthetic natural gas' or 'computer security'

oxytocic - labor inducing

oxytocin - drug used to help a mare expel the placenta and/or let down milk