Case Study: Human-directed Aggression in a Horse

Written by Trudi Dempsey, CHBC


Summary:  A horse who showed signs of aggression towards humans and other horses becomes worse when corrected with physical punishment and natural horsemanship techniques. As a result, he’s placed in a barren environment with minimal social contact. Interventions included constructional aggression treatment, counter-conditioning, and environmental enrichment. With these, as well as time and willingness from the client, human-directed aggression resolved almost completely. 

  • Client: Experienced female horse owner in her 40s
  • Horse’s name: Baron
  • Breed: Welsh Section D
  • Sex: Gelding
  • Age: 5 BIOP: 2 years
  • Height: 15hh
  • Other horses owned by client: One 10-year-old gelding, 16.1hh, and one aged pony gelding, 13hh
  • Accommodation: DIY at livery yard, occasional help from yard owner
  • Exercise: Ridden at least four times weekly, hacking and schooling
  • Presenting behaviour: Biting and kicking when being led, not escalating or intensifying but not improving
  • Medications: None Veterinary referral: Agreed and confirmed no ongoing treatment
  • Feed: One large haynet in stable and hay cobs with chaff given as very small bucket feed when others receive theirs.

Brief history as provided by the client

Baron was purchased from a breeder as a 3-year-old entirely for the purpose of leisure riding and attending local shows. He passed five-stage vetting pre-purchase, gelded before leaving breeder, went directly to trainer to be broken in for riding. When viewed with the breeder (twice in total) Baron was led in a control headcollar or chifney bit. From being weaned at approximately 5 months of age, he had been turned out in an individual paddock within sight of other youngsters.

Baron was turned out with client’s horse and pony (slowly introduced) until he bit the horse, which required stitches. This was apparently an unprovoked attack but the owner only had a fellow livery’s account as she was not present herself when it occurred. There was nothing that (in the client’s opinion) led to or escalated to the attack. This has led to Baron currently being kept in an individual paddock with double electric fencing between him and the other horses (both geldings) on summer turnout regime stabled from around 9.00 a.m. until 4.00 p.m.

Baron had displayed what the owner described as ‘colt-like’ behaviour from when he was purchased two years ago. He would mouth everything from a lead rope to a human arm. He now bites the handler’s arm (has drawn blood) and if corrected intensifies his attack. Behaviour is worse when being led and he will sometimes turn and kick out with his hind legs. This hasn’t escalated or improved since purchase.

Correction with a whip/broom or by yanking down hard on his lead rope was ineffective in reducing behaviour. Natural horsemanship techniques (using a long lunge whip to move his feet and direct him away and a rope halter with a long rope wiggled and shaken towards him to put him back into his own space and away from the client) or ignoring him were not successful either.

Leading to the paddock was particularly difficult as Baron’s field was farthest away, requiring him to pass other horses to get there. It was not possible for him to be turned out first due to client’s work schedule (others would arrive before her). Paddock was so placed as it gave him a corner (hedges to two sides) with only one common fence with another horse to avoid aggression across fence line.

Although the client had been bitten, she had not at any time required medical attention following a bite. More recently precautions were being taken when leading, which involved wearing a jacket with long sleeves and using a nose chain correction headcollar (tightening when put under pressure) to lead with. The rope was directly attached to the chain and held very close up under Baron’s chin.

The client would mount for riding with yard manager holding bridle but once mounted no aggression was shown and he was calm and forward going both in the arena and out hacking on the local lanes and tracks. The incidents of biting had become so commonplace that client could not number them. Baron’s behaviour was no longer escalating but was not diminishing, and client worried that they had not developed any rewarding relationship over the period she had owned him. A consultation visit was scheduled after seeking referral from client’s vet who confirmed there was no ongoing treatment, nor had there been treatment other than vaccinations since the client had owned Baron. Baron was seen to take recumbent sleep, in his stable, by the client.

Living situation and first-hand assessment of the behaviour

Baron was stabled on my first visit, as per his routine for 10.00 a.m. in summer, with the company of client’s other horse and pony in stables within sight. They had spent the night in the paddock. I was given a tour of the paddocks and yard, which gave me time to chat to the client. The paddocks of all the horses were barren environments, but Baron’s particularly so. He couldn’t even reach into a hedge to browse due to electric tape around the whole paddock (due to potential for escape and to avoid him touching neighbours). The grass was short and dry but the paddock was of a good size.

The client explained the system of leading Baron and her other horse together to the field; this was essential as he didn’t like being left in the stable without this horse or being taken to the field ahead of him. There were several sharp turns to manoeuvre around on exiting the stable yard, and with two horses to lead this created pinch points where keeping the horses apart and avoiding escalation of bite threats was difficult.

The client had not mentioned until my visit that Baron would also air bite and attempt to bite her as she entered the stable. In order to assess a baseline for the aggression, I asked the client to approach Baron’s stable as I observed. I asked her to listen carefully to my instructions but to employ her usual safety precautions. At approximately 3m from Baron’s door, there were several changes in his face: ears lying back, eyes triangulating, muzzle and jaw tightening, and nostrils flaring (see table of behaviour). When the owner stepped close enough to reach a hand to the door bolt and simulate opening it, Baron tossed his head towards her, baring his teeth. At this point I asked the client to step away from the stable door.

The client returned to the stable to show me her regular pattern for putting his headcollar on, holding him away from her with one hand whilst putting the rope around the top of his neck with the other. Once the rope was in place Baron stopped trying to bite her but the facial indicators remained the same as I had previously observed. Once the headcollar was on Baron was calmer and the facial indicators became less apparent.

The client tied Baron up on a very short rope while she groomed and saddled him; there were barely any outwardly observable signs of anxiety or any biting during grooming or saddling, even when girthing up or brushing him. Baron showed signs of enjoyment while being scratched on his withers (stopped eating, extended top lip, and twitched nostrils). The client placed the bridle over the headcollar and then, holding him very short with the reins, she proceeded to unfasten the headcollar buckles and remove it from under the bridle. Signs of facial and neck tension accompanied by bite threats were observed.

Leading him out of the stable to the arena, the client held Baron with reins very short and the her hand under his chin. At the mounting block the yard owner took the same hold on the reins and the client mounted. During mounting Baron showed no signs of anxiety (if there had been, I would have stopped the process immediately). Baron walked calmly into the arena on a long rein. In walk and trot he was calm and attentive to Lisa’s cues, responding quickly to light leg and hand aids. On leaving the arena and walking down the farm drive he was equally calm and responsive. Baron was dismounted in front of the stables and again Lisa used the short rein technique to get him back into the stable and untacked. Once the bridle was off Baron began to air bite and the anxious signs of facial tension as recorded earlier were again noted.

Potential triggers considered for behaviour, current and historical

• Pain or disease possible cause or at least contributary factor – ruled out by veterinary investigations following the first consultation.
• Chronic stress due to lifestyle – unable to control environment and therefore adapt. Leads to lower trigger point for aggression and potential cause for Baron’s behaviour towards his field buddy.
• Lack of stimulation due to barren environment – makes it hard for Baron to adapt to his current lifestyle, but this may well have been the case from a very young age so the long-term chronic stress could have been a contributary factor for several years.
• Acute stress triggered by human presence or proximity of another horse. Guarding of personal space. Baron’s behaviour of biting and threatening to bite may have been reinforced previously as it provided an outcome of the human or horse moving away. This was no longer always the case as the client had engaged protocols to prevent the behaviour but it is likely that he was still experiencing the physiological changes associated by his inability to control the proximity of horse or human. It was evident at the first consultation that Baron was triggered when the client (or I) were approximately 3m from his stable door
• Fear of handler/handling and equipment, conditioned response from handling as foal and flooding during training – this is likely to be a contributary factor as he was roughly handled from a young age by the breeder, and the client saw firsthand this behaviour when he was led using a chifney (control bit)
• Fear and frustration from inability to control environment in stable – approach of humans from 3m or closer triggered response (see data sheets)
• Early life (forced and sudden weaning and lack of conspecific social group after weaning), environment inadequate for development of social skills – highly likely to be a contributary factor
• Lack of social group or pair bond, inability to feel safe or understand social signals – potentially led to attack on field buddy
• Early training at 3 years old while physically still immature – physically imbalanced and lacking strength – often native type breeds are erroneously thought to be strong at an early age due to their naturally stocky conformation. This is likely to have been a contributing factor in Baron’s behaviour

Lifestyle changes and training plans

Aggression directed towards humans and horses is not common, and often, as in this case, there are conflicting presentations (behaviour not shown when being ridden, only when handled from the ground). I immediately requested a veterinary investigation to rule out pain triggers for the behaviour. The client agreed to this and I sent a consultation report to the vet. Baron had a full veterinary check-up to investigate any possible physical issues and to rule out gastric ulcers. In their initial checks the vet found no physical reasons for Baron’s behaviour and suggested that behaviour modification plans continue.

Baron’s saddle had been recently refitted by a local master saddler, and as the behaviour was not evident when ridden, it appeared unlikely that poor tack fit was an issue.

During the first consultation I walked the client through a safer protocol for turnout, which involved using a different exit from the stables and a slightly longer distance to the paddock but avoiding the tight turns to exit via the other door. This avoided Baron practising the behaviour of bite threats and biting towards the client and her other horse.

The following environmental enrichment ideas were adopted in the stable:

• Treat ball waiting when he came in from the paddock and after training sessions
• Increased number of haynets in different places in the stable, with different sized holes and at different heights. Client to consider soaking with fruit tea.
• Introduction of a ground feeding hay ball.
• Addition of root vegetable strings and safe hedge browse.
• Book an appointment with an independent nutritionist.

And in the paddock:

• Reveal ‘safe’ areas of hedge for browsing
• Addition of scratching post (previously no place that wasn’t electrified)
• Choice of water – salted or natural (clean, fresh, free-choice natural water always available, choice of small bucket of salted water to add variety and potentially increase salt intake – the average minimum salt intake for 500kg horse of 2 tablespoons of salt [sodium chloride] should be provided daily, between a salt lick and salt within [and added to] short feeds. Begin adding half a teaspoon of salt to a 14-litre bucket and find preference in terms of concentration, never exceeding total salt requirement).  Horses lose at least this amount of salt daily in bodily fluids, and the minimum requirement can increase 2 to 3 times in warmer weather.
• Introduction of safe novel objects – ball, tied flag/bunting
• Salt lick
• Plans for a small-horse safe raised platform
• Plans for introduction of basic ‘umbrella’ shelter
• In the long-term, protocols for reintroduction in paddock of a safe companion

Behaviour modification protocols

Protocol 1: Approaching the stable door

The threshold for Baron reacting to someone approaching his door was approximately 3-5m. The client began walking slowly towards the door (carrying no equipment with her) from 8m away observing Baron and stopping the moment he reacted to her presence (head lift, ear position change, feet moving, tail movement, etc). This determination of threshold should be checked each time before commencing the protocol. As Baron returned to eating hay or all signs of anxiety disappeared the client would step farther away from the door. This was to be repeated up to five times each day between our first and second consultation. Client was very good at observations and comfortable working with this negative reinforcement (termed CAT-H, constructional aggression treatment) technique where Baron could resolve things for himself. In the first five presentations to his door (carried out in my presence) the client built up to approaching within 1m of the door with no reaction from Baron.

Protocol 2: Counter-conditioning for headcollar

To differentiate the approach to the stable door from this protocol, the client carried the headcollar (using my flat headcollar at the consultation and replacing her usual chain control headcollar with a new flat headcollar for future training) in her hand and called his name as she approached the stable. The client put the headcollar over the door as she entered the stable and proceeded to scratch Baron at his withers, at first guarding from any bite threats with her other hand. Baron quickly stopped bite threats once scratching began. The client stopped scratching for a second and immediately recommenced. The gap between scratching was gradually increased to a count aloud of 10. At the end of the protocol the client put two mints into his bucket and left his stable. The shaping plan for this protocol built up to the client being able to step away from Baron and step back for scratching and ultimately to step to the headcollar, pick it up, and return to scratching. The protocol would lead to head collaring, potentially with food reinforcer if the scratches were not sufficiently salient.

Protocol 3: Entering stable for turnout and tacking up to ride

The client will continue to use the control headcollar to lead out and tack up. This is not ideal, but he cannot remain in the paddock 24/7 and needs exercise, so by using different equipment the client can differentiate between the new protocols and the existing association of the control headcollar.

Subsequent visits

Telephone catch-up after six days

The client reported that she had put in place several of the enrichment suggestions for the paddock and stable. Protocol 1 had made good progress and she was able to approach the stable door and rest her hand on the top, and Baron showed no outward signs of stress. We discussed the next steps which would lead her to playing with the bolt on the door and then opening and shutting it without entering, using the same CAT principles of observing reactions and removing herself once he settled back to eat hay or relaxed from any signs of stress.

Protocol 2 had advanced so that the client was able to step to the headcollar, pick it up, and return to scratching with it in her hands.
Using the original turnout as per protocol 3 but avoiding the pinch points on leaving the yard had resulted in no bite threats and removing the headcollar in the paddock using scratches was simple to do.

Training session 3 weeks after initial consultation

Changes had been implemented in the paddock which included:

• The electric tape had been removed from one side of hedge and horse-appropriate fencing used to bridge any potential escape gaps. This allowed for hedge browsing.
• A telegraph pole had been ‘planted’ within the field and two old broom heads had been fixed to it. Presence of hairs provided evidence of its use.
• Water buckets had been placed in different areas in the paddock and although Baron was still primarily drinking plain water, he had shown an interest in the salted water.
• Every three or four days a new ball, flag, or similar had been placed in the paddock and Baron showed great interest in investigating it.
• Several different salt licks were placed in different locations
• Treat ball or food scatters were provided once the head collar was removed on turnout.
• Some of these changes had also been implemented in the other horse’s paddocks.

And in the stable:

• Having tried her other horse’s treat ball, the client had preferred making her own treat dispenser from large plastic bottles (less noisy) and Baron had one in his stable each time he returned to it.
• Baron hadn’t eaten any of the soaked hay, but client had added several different haynet tie rings and an old sack bag with a small hole to pull hay from.
• Carrots were hidden in hay nets before she left him stabled.
• Appointment with nutritionist booked

Protocol 1

On threshold test the client could walk right up to the stable door with no response from Baron. On the first approach the client walked to the stable door, rattled the bolt, and stepped away. Baron didn’t raise his head from eating. On second approach the client repeated the approach but opened the door and let it stand open. Again, no response from Baron, so she shut the door and walked away. We discussed the shaping plan for this protocol and how it would now move directly into protocol 2 (termed “switchover”).

Protocol 2

Merging protocol 2, with client still observing on the approach to stable as in protocol 1. Leaving headcollar on stable door and approaching Baron. As client approached him, Baron turned his head towards her and client waited for him to straighten head before approaching and scratching. After two scratching periods she removed herself and the headcollar from the stable. The client’s grasp of observing and reacting to Baron’s behaviour was excellent as was the progress in both protocols. The client reported calmer leading in the control headcollar and the bridle but was concerned that sometimes scratching didn’t seem to reinforce him sufficiently when they were outside of the stable area. We introduced food as a reinforcer in protocol 2, and Baron remained remarkably calm; no signs of stress were noted. The client began hand-feeding hay cobs which due to the longer chew time, as they were dry, gave her time to build a gap between feeding. During this visit we moved from feeding while standing at his side on entry to the stable to moving a step away (back or sideways) and stepping back to feed. No marker (other than the client getting the food from her bag) was added to avoid making the protocol too complex for the client.

Training session 7 weeks after initial consultation

The client was now able to headcollar Baron following the merged protocol 1 and 2. On this visit the client led Baron for the first time in the flat headcollar out of the stable. The only sign of stress was shown as she turned to walk him back into the stable. We discussed how thinking ahead could help her avoid those situations that suddenly put them in close proximity to each other. We introduced a walk/stop/feed pattern to help this.
After a break the client returned to the stable with tack, and using protocol 2 with food, she bridled Baron. As he had already left the stable using the flat headcollar in this session, we agreed to remove the headcollar on this occasion without leading him out but that the client would try this in the next session. Client reported that Baron left the stable the next day wearing bridle and saddle with no observable signs of stress using stop and feed pattern every few steps.

Following online training sessions

Due to reinstatement of COVID restrictions, the last sessions were by telephone and Zoom. The client continued to work with the merged protocol 1 and 2 using either the flat headcollar or the bridle. When tacking up for riding the control headcollar was no longer used. After several weeks practising leading out of the stable in the flat headcollar the client began to use the flat headcollar to turn out, the first few times with help from someone to lead her other horse, and then leading them both herself. The client handling both horses together proved too much for Baron (his social behaviour with client’s other horse is as yet unresolved, and the client was unable to keep them completely separate during leading to turnout), and triggered bite threats. As the client found it hard to concentrate on her observations of him and avoid these triggers, she agreed to pay the yard owner to help in turning the horses out.

The client is understandably still reluctant to turn Baron out with another horse, but she has asked the yard owner if she could make a horse-friendly post and rail segment between Baron and her other horse so that they can touch noses safely over the fence.


The client continues to text updates, and reports that incidents of Baron biting have reduced to zero. He continues to occasionally air bite if the client suddenly turns him or if he finds himself closer to her other horse on turnout, but these incidents are at most one per week. Baron is calmly tacking up in his stable and leading out (they continue to shape and add duration, so taking about 10 stops in the walk/stop/feed pattern, to reinforce on the way to the mounting block). The client no longer needs help at the mounting block. Whilst there remains a need for improvement in some areas of his handling, Baron is spending barely any time practising his stress-induced behaviours in proximity to humans and horses. The ultimate goal of turning him out with conspecific company is still to be achieved. With the addition of enhancements to his handling and his environment he should continue to make progress. The client is fully aware of the possibility of a relapse due to psychological stress and continues to be observant and careful in all handling. She continues to make improvements to his environment. The outcome of this case relied on excellent observation skills and attention to detail in the protocols by the client.

Appendix: Data Collection

This is a binary data collection taken live in a consultation. Was the behaviour seen/not seen?

Trudi Dempsey is an IAABC-certified horse behaviour consultant, and an ABTC-accredited animal behaviourist and trainer, specialising in clicker training and bitless riding. Trudi can be reached at

Dempsey, T. (2021) Case study: Human-directed aggression in a horse. The IAABC Foundation Journal 20, doi:10.55736/iaabcfj20.5