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.

MACERATION:
Softening or dissolution of skin cell layers, resulting from overexposure to moisture or topical medications.
MACROPHAGE:
A specialized white blood cell of central importance to the body; it ingests cellular debris and foreign material, destroys ingested microorganisms, processes ingested antigens as an initial step in the induction of a specific immune response, and synthesizes a number of important enzymes, coagulation factors, and messenger molecules; also referred to as a mononuclear phagocyte.
MACULE:
A discolored area of skin that is not elevated above the skin surface.
MALABSORPTION:
Faulty absorption of nutrients by the intestine.
MALASSIMILATION:
Defective transport of one or more nutrients from the intestinal contents across the intestinal wall.
MALDIGESTION:
Faulty digestion.
MALIGNANT:
Capable of spreading and invading other tissues; said of tumors.
MAMMARY GLAND:
Breast.
MANDIBLE:
The lower jaw.
MANE-CHEWING:
A stable vice exhibited primarily by yearlings and two-year-olds.
MANIA:
Frantic behavior.
MAST CELL:
A specialized, granule-containing cell found in the skin and lining of the inner body surfaces; it plays a central role in the development of allergy.
MASTICATION:
The action of chewing.
MASTITIS:
Inflammation of one or more mammary glands.
MASTOCYTOSIS:
Abnormal infiltration of mast cells into a body tissue.
MATERNAL IMMUNITY:
A form of temporary immunity that is passed from the mare to the foal in utero (in the uterus) and/or after birth in the colostrum and milk; primarily antibody, maternal immunity serves to protect the foal until its own immune defenses become fully operative.
MAXILLA:
The upper jaw.
MECHANICAL VECTOR:
A vector that merely serves physically to transport a parasite from one host to another.
MECONIUM:
The contents of the foal's first bowel movement.
MEDIAL:
Closer to the midline of the body.
MEDIAL CANTHUS:
The inner corner of the eye.
MEDULLA:
The innermost part of an organ (kidney, adrenal gland, brain) or hair shaft; contrasted with cortex.
MEGACALORIE (MCAL):
One thousand kilocalories; a useful term for quantifying the energy in a ration.
MEGAKARYOCYTE:
A giant cell found in the bone marrow; it is the precursor of the blood platelets.
MEIOSIS:
Process involved in the formation of gametes (reproductive cells), wherein cell division produces new cells (spermatozoa and ova) containing only one set of chromosomes.
MELANIN:
Dark pigment of skin and hair.
MELANOBLASTS:
Immature melanin-forming cells that originate early in fetal life.
MELANOCYTES:
Cells of the epidermis, the outermost layer of the skin, that produce the skin pigment melanin.
MELANOCYTE-STIMULATING HORMONE (MSH):
Hormone produced by the pituitary gland that mediates the deposition of melanin (dark pigment of skin and hair) in the body.
MELANOMA:
A (usually) malignant tumor of pigmented skin cells.
MELANOTRICHIA:
Abnormal darkening of the hair color.
MELENA:
Dark, pitchy stool caused by bleeding into the digestive tract.
MELIOIDOSIS:
A glanderslike disease caused by Pseudomonas pseudomallei, characterized by the development of nodules in internal organs; not known to occur in the United States.
MENINGES:
The three protective membranes surrounding the brain and spinal cord; specifically, the dura mater, pia mater, and arachnoid.
MENINGITIS:
Inflammation of the meninges.
MERONT:
Alternative term for schizont.
MEROZOITES:
The daughter cells resulting from either schizogony or endodyogeny (asexual forms of reproduction in certain protozoa).
MESENTERIC:
Pertaining to the mesentery, the membrane that lines the abdominal organs and attaches them to the body wall.
MESOVARIUM:
Fold of tissue that holds the ovaries in place.
METABOLIC ENERGY (ME):
The caloric content of a diet; can be roughly estimated from the proximate analysis.
METABOLIC WATER:
Water the body obtains from solid food and the breakdown of ingested fat, carbohydrate, and protein.
METABOLISM:
All the life-sustaining biochemical processes in the body; the conversion of nutrients into energy.
METABOLITES:
By-products of metabolism.
METABOLIZABLE ENERGY (ME):
The difference between the gross energy of a food and the energy that is lost in urine and feces.
METACERCARIA:
Infective larval form of flukes that arises from the cercaria stage.
METAPHYSIS:
The region immediately beneath the growth plate (epiphysis) of a bone.
METASTASIS:
Spread of tumor cells from the primary tumor site to distant body sites; a characteristic of malignant tumors.
METESTRUS:
In the estrus cycle, the period of subsidence of follicular activity that follows estrus ("heat").
METRITIS:
Inflammation of the uterus.
MICROBE:
Any minute living organism, particularly one capable of causing disease; viruses, because they are not living organisms, technically are not considered "microbes," but are more correctly referred to by a term such as "infectious agent."
MICROVASCULATURE:
The smallest blood vessels (capillaries).
MILLER'S DISEASE:
Colloquial term for nutritional secondary hyperparathyroidism.
MINERALOCORTICOIDS:
Corticosteroids whose primary function is regulation of water and electrolyte balance; they act by retaining sodium and excreting potassium within the kidney tubules.
MINIMAL INHIBITORY CONCENTRATION (MIC):
Laboratory test procedure for determining the sensitivity or resistance of a bacterial isolate to several antibiotics.
MIOTIC:
Any ophthalmic medication that causes the pupil to contract.
MIRACIDIUM:
Free-living larval form in the life cycle of flukes.
MITICIDE:
Any medication that kills mites.
MITOCHONDRIA (SINGULAR: MITOCHONDRION):
Specialized structures within body cells that are responsible for producing energy.
MITOSIS:
Process wherein a body cell divides into two exact copies of itself, each new cell receiving two complete sets of chromosomes.
MITOTIC:
Actively undergoing cell division.
MITRAL REGURGITATION:
Partial backflow of blood through a dysfunctioning mitral valve.
MITRAL VALVE:
The atrioventricular valve on the left side of the heart.
modified-live virus:
Attenuated (weakened) virus that no longer produces clinical disease in the host but retains the ability to induce a protective immune response, and can be used as a vaccine; technically a misnomer, since viruses are not living organisms.
MOLARS:
The large grinding teeth.
MOLDY CORN POISONING:
Common name for leukoencephalomalacia.
MONENSIN:
Feed additive for cattle and poultry; toxic for horses.
MONOCULAR FIXATION:
Focusing of one eye on an object.
MONOCYTE:
Nondescript white blood cell found in the circulation, which converts into an active macrophage upon entry into tissue.
MOON BLINDNESS:
Periodic ophthalmia.
MORPHOGENESIS:
The progressive development of form and shape of an organism, or of an individual organ or tissue within the organism.
MORPHOLOGY:
The shape and structure of an organ or of an entire organism.
MOTILE:
Capable of movement.
MOTILITY:
Ability to move.
MOTONEURON:
A nerve cell that supplies myofibers in skeletal muscle.
MOTOR UNIT:
The basic functional and anatomical organization of nerves and muscle fibers within skeletal muscle.
MUCOCILIARY ESCALATOR:
A coordinated and forceful wavelike movement of the cilia lining the air passageways from the trachea to the bronchioles; essential for the normal removal of mucus and inhaled particulate matter and bacteria.
MUCOCUTANEOUS JUNCTIONS:
Areas where mucous membranes and skin adjoin, such as the lip margins.
MUCOID:
Resembling mucus.
MUCOMETRA:
Presence of mucus in the uterus.
MUCOSAL-ASSOCIATED LYMPHOID TISSUE (MALT):
Lymphoid tissue associated with the linings of the digestive, respiratory, and urogenital tracts.
MUCOUS MEMBRANES:
Lubricating membranes lining the internal surfaces of body cavities, such as the mouth, digestive tract, respiratory tract, and urinary tract.
MUCUS:
Slimy substance secreted by certain membranes (mucous membranes); contains a variety of secretions, salts, and cells.
MULTILOCULAR:
Having many compartments.
MULTIPLE MYELOMA:
An uncommon malignant tumor of plasma cells arising from the bone marrow.
MURMUR:
An abnormal heart sound produced when blood flows too rapidly or too chaotically through a portion of the heart; a common sign of heart disease.
MUTATION:
A permanent genetic change, sometimes resulting in altered structure or function.
MYCETOMA:
General term for a swollen, progressing, tumorlike skin lesion caused either by fungi or certain bacteria.
MYCOLOGY:
The study of fungi.
MYCOPLASMAS:
Microscopic organisms closely related to bacteria that are ubiquitous inhabitants of the respiratory and genital tracts.
MYDRIATIC:
Any ophthalmic medication that dilates the pupil.
MYELIN:
Fatty substance forming the outer tunic (myelin sheath) around many nerve axons; facilitates the conduction of nerve impulses along the axons.
MYELOGENOUS:
Originating within the bone marrow.
MYELOPATHY:
General term for any degenerative disorder affecting the spinal cord.
MYIASIS:
Infestation of body tissue by fly maggots.
MYOCARDITIS:
Inflammatory heart-muscle disease.
MYOCARDIUM:
The muscular layer of the heart; heart muscle.
MYOCLONUS:
Involuntary rapid, jerky twitching or contraction of muscles.
MYOFIBERS:
Muscle fibers.
MYOFIBRILS:
Slender threadlike structures, bundles of which make up each muscle fiber.
MYOFILAMENTS:
Smaller threadlike elements making up the myofibrils of muscles.
MYOGLOBIN:
The oxygen-transporting pigment of muscle tissue.
MYOGLOBINURIA:
Presence of myoglobin in the urine.
MYONECROSIS:
Muscle-cell death.
MYOPATHY:
General term for any muscle disorder.
MYOSIN:
A vital protein component of muscle, one of the proteins responsible for muscle contraction.
MYOSITIS:
Muscle inflammation.

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