Horse Health Glossary

Not sure what that veterinary word means? Look it up below!

Reprinted with permission from the University of California, Davis, The Book of Horses edited by Mordecai Siegal.

OBLIGATORY PARASITE:
A parasite whose life cycle cannot be completed without a parasitic phase at some stage.
OCCLUDE:
To close off or obstruct.
OCCLUSION:
The fit or "bite" of the upper and lower teeth together when in contact following closure of the mouth.
OCULAR:
Pertaining to the eyes.
OLECRANON:
The point of the elbow.
OLECRANON BURSITIS:
Bursitis caused by repeated trauma to the point of the elbow; also called shoe boil.
OLFACTORY:
Pertaining to smell.
OLFACTORY NERVES:
Nerves found in the nasal turbinates in which the sense of smell originates.
OLIGURIA:
Reduction in the amount of urine excreted.
OMPHALOPHLEBITIS:
Infection (usually bacterial) of the veins of the umbilical cord in the newborn; "navel ill."
ONCOGENESIS:
The process of tumor development.
ONCOLOGIST:
Cancer specialist.
OOCYST:
An encapsulated ovum (egg) of a sporozoan parasite such as Toxoplasma gondii, usually excreted in the feces.
OOCYTE:
Developing egg cell (ovum) in the ovary.
OPACIFICATION:
Loss of transparency.
OPACITY:
An opaque area or spot, as in the lens or cornea of the eye.
OPEN REDUCTION:
Any procedure to repair a fracture wherein the broken bone is exposed surgically.
OPERANT CONDITIONING:
"Trial and error" learning, usually involving a reward.
OPHTHALMOSCOPE:
Instrument for viewing the interior of the eye.
OPPORTUNISTIC PATHOGEN:
Any organism that is able to induce disease only if the host's immune or other defenses are compromised.
OPTIC DISK:
That portion of the optic nerve visible at the surface of the retina; also called optic nerve head.
OPTIC NERVE:
Literally an extension of the brain, which reaches to the back of the eye (retina) and transmits signals derived from light energy that are translated into a visual image by the brain.
OPTIC NEURITIS:
Inflammation of the optic nerve.
ORCHITIS:
Inflammatory disease of the testicle.
ORGAN OF CORTI:
The spiral-shaped organ of hearing within the inner ear, containing specialized sensory receptors.
OROPHARYNX:
The back of the throat; tonsillar area, between the soft palate and epiglottis.
OSSELETS:
Puffiness around the fetlock joint.
OSSEOUS:
Bony.
OSSICLES:
Very small bones.
OSSIFICATION:
The formation of bone.
OSSIFYING MYOPATHY:
Condition most commonly affecting the hindlimbs of the horse, in which scarring and/or bone formation occurs within injured muscles.
OSTEITIS:
Inflammation of a bone.
OSTEOBLAST:
A bone-forming cell.
OSTEOCHONDRITIS DISSECANS (OCD):
Cartilage disorder characterized by the presence of large flaps of cartilage or loose cartilaginous bodies within a joint.
OSTEOCHONDROSIS:
A disorder of growing cartilage that may affect either the growth plate or the articular cartilage.
OSTEOCYTE:
Cell type in bone that, in response to certain hormones, is responsible for maintaining normal calcium and phosphorus levels in the bloodstream.
OSTEOMYELITIS:
Infection of a bone accompanied by pus formation; usually caused by bacteria.
OSTEOPENIA:
Loss of bone calcium.
OSTEOPOROSIS:
Thinning and weakening of bone.
OSTEOSARCOMA:
A malignant tumor of bone.
OSTEOTOMY:
Surgical cutting of bone.
OTITIS EXTERNA:
Inflammation of the outer ear.
OTITIS INTERNA:
Inflammation of the inner ear; also called labyrinthitis.
OTITIS MEDIA:
Inflammation of the middle ear; also called tympanitis.
OVARIAN FOLLICLE:
An ovum (egg) and its surrounding cells.
OVARIECTOMY:
Surgical removal of one or both ovaries.
OVARIES:
Paired organs of the female responsible for the production of ova (eggs).
OVARIOHYSTERECTOMY:
Surgical removal of the uterus and ovaries.
OVERO:
Recessive equine coat-color pattern, consisting of a colored base coat with white patches and colored legs. The white markings are more irregular than the colored patches of the tobiano. White does not cross the back and the head is mostly white.
OVIDUCTS:
Uterine or fallopian tubes.
OVOTESTES:
Abnormal gonads containing both testicular and ovarian tissue.
OVULATION:
Release of an egg from an ovary.
OVUM (PLURAL: OVA):
Egg.
OXIDATION:
The cellular "burning" of glucose, amino acids, and fatty acids to produce energy in the form of adenosine triphosphate (ATP), the major form of energy used by cells.
OXYGENATED:
Filled with oxygen; said of arterial blood.
OXYTOCIN:
A hormone formed in the hypothalamic region of the brain and stored in the pituitary gland; it stimulates contraction of the uterus and milk ejection from the mammary glands.

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