OBESITY - Excessive accumulation of body fat resulting in abnormally high body weight. O12507. Definition from Hurnik et al., 1995.

OBSERVATIONAL LEARNING - Learning by observing the behavioral responses and reinforcement of other individuals. Observational learning also 5 called vicarious learning. O12514. Definition from Hurnik et al., 1995.

OCCUPATIONAL VACUUM - A state of seriously thwarted motivation of an organism to interact with its environment, caused either by diminished novelty or unarousing surroundings. Occupational vacuum can also be generated by inability of the organism to interact with its surroundings due to extended physical or psychological restraint, O12607. Definition from Hurnik et al., 1995.

ODDITY TRAINING - A series of discrimination trials in which the correct solution is characterized by being different from a group of alternatives. The learning set to be acquired involves the principle that the correct alternative learning set to be acquired involves the principle that the correct alternative to choose has features not shared by any other alternative. O12611. Definition from Hurnik et al., 1995.

ODOR - Sensation caused by chemical stimulation of receptors in the mucous membranes of the nasal cavities. Also see specific odor - GROUP. O12612. Definition from Hurnik et al., 1995.

OESTRUS - See Estrus. O12613. Definition from Hurnik et al., 1995.

OFFENSIVE AGGRESSION - Unprovoked aggression. In a social context, offensive aggression is not manifested in response to aggression instigated by another individual, but is an attempt to gain some resource at the expense of the individual toward which it is directed. O12614. Definition from Hurnik et al., 1995.

OFF FEED - Referring to loss of appetite for food. (colloquial term) O12615. Definition from Hurnik et al., 1995.

OFF SIDE (horse) - See Far Side. O12616. Definition from Hurnik et al., 1995.

OFFSPRING PREFERENCE - Preference of a young animal to associate with and receive care from a particular adult(s). Such a preference may be expressed at more than one level, e.g., preference for a parent versus another adult, or for one parent versus the other. O12614. Definition from Hurnik et al., 1995.

OILING - A component action of preening in which a bird uses its beak to spread oil secreted by the uropygial gland over its plummage. Oiling helps to keep the feathers in good condition. O12702. Definition from Hurnik et al., 1995.

OMEGA ANIMAL - An animal that ranks lowest socially in its group Compare: Alpha Animal. O12711. Definition from Hurnik et al., 1995.

OMNIVOROUS - Subsisting on feed of both plant and animal origin. O12712. Definition from Hurnik et al., 1995.

OPEN-FIELD BEHAVIOR - Behavior manifested and/or studied in an open-field test situation. O12716. Definition from Hurnik et al., 1995.

OPEN-FIELD TEST - Exposure of an organism to some standardized environmental arrangement, apart from that where it normally resides, in order to study its approach-avoidance responses or signs of emotionality. O12717. Definition from Hurnik et al., 1995.

OPERANT CONDITIONING - A type of conditioning in which reinforcement is contingent on a given operation (e.g..bar pressing). In operant conditioning it is unimportant what technique the animals use to conduct such an operation; the response may be somewhat variable as long as the operation is performed. O12720. Definition from Hurnik et al., 1995.

OPTHALMIA - Contagious inflammation of the eye, affecting mainly sheep and goats O12803. Definition from Hurnik et al., 1995.

ORAL - Pertaining to the mouth. O12807. Definition from Hurnik et al., 1995.

ORAL TENDENCY - Tendency to examine objects using the mouth. Normally, oral tendencies are common in very young mammals. Artificially, they can be induced by bilateral temporal lobectomy. O12808. Definition from Hurnik et al., 1995.

ORGASM - The culminating point of sexual excitement associated with distinct physiological and behavioral characteristics such as high vasopression rhythmic muscular contractions, and semen ejaculation (in males). O12815. Definition from Hurnik et al., 1995.

ORTS - The remains of feed in a trough or feeder that an animal(s) refrains from eating. O12903. Definition from Hurnik et al., 1995.

OUTDOOR HOUSING - A housing system where animals are kept predominantly or continuously outdoors. Outdoor housing facilities usually have simple shelters to provide protection against weather extremes. O12912. Definition from Hurnik et al., 1995.

OVERCROWDING - An excessively high spatial density of animals due to some abnormal environment (e.g., inadequate space caused by physical constraint or avoidance of an inhospitable area). Overcrowding compels breakdown of individual distance zones and, in extreme circumstances, extend their limbs without interference, or have adequate opportunity for extend their limbs without interference, or have adequate opportunity for eating or drinking- The consequences of overcrowding depend on its intensity and duration, and thus may range from frustration, boredom, elevated competition for space, and towered cleanliness in the pen to serious behavior anomalies (stereotypy, lethargy, learned helplessness), high levels of aggression, nutritional deprivation, inability to maintain effective thermoregulation and increased mortality. Compare: Crowding. O13014. Definition from Hurnik et al., 1995.

OVERINCLUSION - Inability to inhibit an undesirable response associated with a particular stimulus. O13001. Definition from Hurnik et al., 1995.

OVERLEARNING - Continuation of learning trials beyond the stage necessary for required retention. O13002. Definition from Hurnik et al., 1995.

OVERLYING (swine) - Incidental lying down by a sow onto piglets, causing their injury or death. O13003. Definition from Hurnik et al., 1995.

OVER REACH (horse) - Defective leg action causing the hoof of the hind leg to touch the heel of the foreleg. O13004. Definition from Hurnik et al., 1995.

OVINE - Sheep or pertaining to sheep. O13009. Definition from Hurnik et al., 1995.

OVIPOSITION - The act of expulsion of fully developed eggs from the body. O13011. Definition from Hurnik et al., 1995.

OX - A castrated male bovine used in draft work. O13014. Definition from Hurnik et al., 1995.

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Revised: April 18, 2008