- Definition
- Pathophysiology
- Systems Affected
- Genetics
- Incidence/Prevalence
- Geographic Distribution
- Signalment
- Signs
- Causes
- Risk Factors
BASICS
- Behaviors that do, or attempt to do, injury to another with the apparent motivation of causing harm
- Agonistic behaviors include threats, offensive aggressive behaviors, defensive behaviors, and submissive behaviors
- Aggression occurs in specific contexts or circumstances and is influenced by numerous variables, including internal states, external stimuli, learned experiences, etc
- It can be classified in numerous overlapping categories, e.g. according to the target, function, motivation, whether offensive or defensive
- Aggression usually is a normal, species-typical behavior but can be triggered by anxiety, fear, and underlying pathophysiologic conditions that result in pain or endocrine and CNS abnormalities. Underlying conditions may be acute or chronic as well as intermittent. Consequently, corresponding aggression may vary in intensity and frequency
- “Grouchiness” or “irritability” may be related to low or moderate levels of pain
- Endocrine and gonad abnormalities, e.g., hypertestosteronism and ovarian and ovarian tumors in mares, retained testicles in males
- CNS disorders, e.g., encephalopathies, rabies, irritating or ablative lesions
- Low serum serotonin levels have been associated with aggressive behavior, stress, and illness
- Many physiologic and behavioral systems can be affected
- Musculoskeletal, skin, ophthalmic injuries may be incurred due to aggressive behaviors
- Reproductive behaviors may be interrupted
- Horses may exhibit aggression towards members of the same sex to disrupt courtship and copulation. Some breeding stallions managed “in-hand” are aggressive to the mare and handlers
- Some mares are aggressive towards their foals. In free-ranging situations the foal may not survive; in a controlled environment, successful intervention is possible. Some mares aggressively defend their foals against other animals, including people
- Aggressive outbursts can severely affect the human-animal bond and consequently impair a horse's welfare
- Frequent or prolonged states of aggression can result in chronic stress and result in changes in the hypothalamic–pituitary–cortical continuum. Chronic stress can affect immune function, body maintenance
- Interference with learning and performance
Genetics has been shown to influence specific types of aggressive behaviors in many species, but the mechanisms are unknown.
Aggressive protection of foals is reported more often in Arabian mares.
- Any age
- Playful aggression is most common in young horses and colts
- Intraspecific, intermale aggression is more common and intense in mature males
Aggressive behaviors range from mild threats to intense injurious acts.
- Mild forms include laying back of ears, lowering and extending head, nodding or swinging of head and neck, shifting of hindquarters toward another sometimes with mild pushing
- Moderate aggression adds threats to bite, strike or kick, tail switching, sometimes slight hopping motions with rear quarters, head and body bumping, harsh vocal squeals. There is an apparent restraint in intensity and effort
- High levels of aggression include serious efforts to bite, strike, or kick, severe bites, and attempts to knock opponent off balance. Rearing and striking with forelegs (boxing)
- Play aggression includes components of above but of low intensity, usually not causing any or serious harm between unshod horses
- Defensive behaviors include moving away and/or shifting rear quarters toward aggressor
- Offensive behaviors usually involve a head-on approach and threat
- Submissive behaviors include deferring to more dominant animal and “snapping” (jaw-waving, teeth-clamping, or unterlegenheitgebärde). Sometimes a slight sucking sound occurs. The ears are usually in a somewhat horizontal position
- Mares with elevated testosterone levels may show “stallion-like” behaviors, e.g. mounting other mares, vocalizing like a stallion, herding other mares, and aggression to other horses
- Ask questions to identify exactly what behaviors are occurring. Determine when, where, how often they occur, when did they start and how did they progress, the targets of the aggression; the situations that tend to make it worse and situations when it does not occur; and what has been done thus far to deal with the problem. These answers form the basis for diagnosis, treatment, and risk assessment
- Aggressiveness associated with endocrine abnormalities is generally of gradual onset
- Examine carefully for pain. Chronic vertebral problems are often overlooked as a source of pain and aggression or grouchiness in riding horses
- Reproductive tract abnormalities, including retained testicles. Mares may have ovarian abnormalities, enlarged clitoris, blind vaginal sac, “cresty neck”
- Pain
- Fear/defense
- Play aggression usually is inhibited and causes few serious injuries among unshod horses of similar ages and weight; however, play can cause serious injury to people
- Protective—occurs in defense of other animals or people with whom the aggressor has a relationship and that are perceived to be under threat
- Dominance—hierarchies exist in groups of horses and are usually initially established via aggression, threats, and reciprocal deference. Once hierarchies are established and there is sufficient opportunity for the subordinate horse to defer, high levels of aggression rarely occur
- Resource guarding—food, preferred pasture partners, water, shelter, etc. Usually directed toward other horses but can be directed toward people
- Redirected—occurs during conflict situations in which a horse attacks another animal or person when access to the original target is blocked
- Redirected aggression occurs when a horse is motivated to be aggressive but is either physically or psychologically prevented from aggressing the eliciting stimuli and, instead, redirects the aggression to another target
- Infanticide—stallions may kill foals that are not theirs or are not recognized as theirs
- Sex related—occurs as part of courtship, copulation, or intrasexual competition
- Endocrine abnormalities
- CNS abnormalities such as encephalitis. Rabies may be manifested as “dumb,” “furious,” “paralytic,” or any combination as well as other pathologic signs. These horses may be violent and, in attempts to control them, handlers are exposed to saliva and biting
- Inappropriate use of punishment and mismanagement
- Small enclosures and poorly designed enclosures that prevent escape or deferral to threats
- Inadequate designs of water and feeding sites that result in fighting over access to resources
- Indiscriminate hand feeding treats can lead to “nipping”
- Adjacent stabling of horses that exhibit aggression toward each other
- Insufficient exercise
- Foals reared in isolation from other horses may not develop adequate social skills and may develop inappropriately rough play aggression with people
DIAGNOSIS
TREATMENT
MEDICATIONS
FOLLOW-UP
MISCELLANEOUS