Dually investigated: The effect of a pressure headcollar on the behaviour, discomfort and stress of trained horses

Highlights

• Dually headcollars increase pressure, intended to improve compliance in horses.

• Horses did not complete handling tests faster in the Dually, compared to Control.

• Horses tended to refuse more proactively in the Dually, compared to Control.

• Trained horses refused more proactively than Naïve horses in the Dually.

• Stress and Horse Grimace Scores were not higher in Dually than Control.

Abstract

The Dually™ is a control headcollar designed to improve equine behaviour during handling challenges by applying greater pressure than a standard headcollar. Previous research indicated it did not improve compliance in naïve horses but did result in higher Horse Grimace Scale scores (HGS) indicative of discomfort. However, subjects had not been trained to step forward to release the pressure applied by the headcollar. The current study aimed to determine the effect of training on behaviour and physiology of horses wearing the Dually™ headcollar during handling challenges. To this end, subjects received three training sessions prior to completing two handling tests in which they crossed distinct novel obstacles, one wearing a Dually™ with a line attached to the pressure mechanism and one attached to the standard ring as a control. Behaviour was coded by hypothesis blind researchers: time to cross the obstacle and proactive refusal (moving away from the obstacle) were recorded as indicators of compliance and the Horse Grimace Scale was used to measure discomfort caused by each configuration of the device. Infrared thermography of ocular temperature, heart rate variability (RMSSD and low/high frequency ratios (LF/HF)) and salivary cortisol were measured as indicators of arousal. Data from the previous study on Naïve horses was also included to compare responses to the Dually in Naïve and Trained horses. Training resulted in a decrease in RMSSD (p = 0.002) and an increase in LF/HF (p = 0.012), compared to rest, indicating arousal. As per the original study, horses did not complete the tests more quickly in the Dually, compared to control (p = 0.698). Trained horses from this study tended to be more proactive in the Dually compared to Controls (p = 0.066) and significantly more so than Naïve horses from the previous study (p = 0.002) suggesting that behaviour becomes less desirable during early Dually training. Yet, stress and HGS indicators were not higher in the Dually compared to Control during testing. Results suggest the Dually has a negative effect on behaviour but not on stress or discomfort during short handling challenges. Further research is warranted to determine the long-term effect of Dually experience on behaviour and welfare.

Introduction

The horse is a large prey animal for which domestication has dampened, but not extinguished, innate biological flight responses (Brubaker and Udell, 2016). These responses make it difficult to retain stimulus control at all times (McGreevy and McLean, 2007) as environmental stimuli often exert more control over the horse’s behaviour than their human handler is able to. Williams and Ashby (1995) state 20 % of accidents occur during handling and allude to horse behaviour being the primary cause. Similarly, Sandiford et al., (2013) reported 12 % of patients admitted to a UK hospital with horse related injuries sustained them in non-ridden accidents. Therefore, it is understandable that many owners seek solutions to reduce such risky behaviour during daily interactions, often by using devices which increase the salience of human cues in order to compete with environmental stimuli.

The Dually™ headcollar is a widely used, commercially available control headcollar which increases the pressure a handler can apply in order to maintain control of a horse. It therefore works using negative reinforcement: pressure from the headcollar should release when the horse offers the desired response. It has two settings: a standard ring under the chin and two side rings which operate an inbuilt pressure-release mechanism. When the lead-rope is attached to the side ring, if the horse pulls back or fails to walk forward when pressure is applied by the handler, the inbuilt mechanism tightens, increasing the level of pressure exerted around the jaw and nose of the horse (Roberts, 1999). The patent for the Dually™ states “It is extremely effective for training the animal to lead, to stand still, to walk into a truck or trailer, to walk slowly through narrow passages, to walk over unfamiliar objects…” (Roberts, 1999). However, research investigating bridles which apply pressure to similar sensitive facial structures highlights welfare concerns (Doherty et al., 2017; Fenner et al., 2016; McGreevy et al., 2012). Further, Ijichi et al. (2018) found the Dually™ did not improve compliance in naïve horses but did result in higher Horse Grimace Scale scores (HGS). However, in the previous study, subjects were naïve to the Dually™ and had not been trained to give the desired response, resulting in release of pressure. Therefore, the headcollar may still be valuable in modifying the behaviour of horses that are trained to offer the desired response to release the pressure.

The aim of the current study was to determine the effect of the Dually™ on behaviour and physiology of trained horses during handling challenges. To this end, subjects received three training sessions prior to completing two novel handling tests, one wearing a Dually™ with a line attached to the pressure mechanism and one attached to the standard ring as a control. Each test consisted of crossing two different novel objects to avoid habituation. Time to cross the obstacle and proactive refusal (moving away from the obstacle) were blind scored as indicators of compliance (Ijichi et al., 2013). The Horse Grimace Scale was scored by an observer blind to the experimental study design (Dalla Costa et al., 2014). Ocular temperature measured by infrared thermography (IRT) (Yarnell et al., 2013), heart rate variability (HRV) (von Borell et al., 2007) and salivary cortisol (Hughes et al., 2010) were measured as indicators of stress and arousal. Data from the previous study on naïve horses completing similar tests (Ijichi et al., 2018) was also included to compare the responses of trained and naïve horses. Results were compared between Control and Dually™ in Trained horses and between Naïve and Trained horses. It was hypothesised that Dually™ Training would result in improved compliance, and reduced arousal and HGS scores compared to Naïve Dually™ horses and improved compliance compared to Trained Control.