L V B Diop

O Isnard

A magnetic study of the HoCo12-xFexB6 ferrimagnetic compounds

The effects of Fe substitution on the structural and magnetic properties of the HoCo12-xFexB6 (0 ≤ x ≤ 2) series of intermetallic compounds have been studied. All of the compounds form in the rhombohedral SrNi12B6-type structure, the lattice constants increasing linearly with x.

These compounds are ferrimagnets with a small transition metal magnetic moment and exhibit a spin reorientation transition. The Curie temperature decreases from 147 K for x =0 to 105 K for x = 2. The Fe for Co substitution leads also to a progressive decrease of the spontaneous magnetization. The spin reorientation transition temperature is significantly reduced upon Fe for Co substitution whereas the compensation temperature is much less sensitive to the Fe composition.

Introduction

Intermetallic compounds based on rare-earth elements (R) and 3d transition metals (TM) form an important class of materials with various applications such as permanent magnets, magnetostrictive devices, or magneto-optical recording. The outstanding magnetic properties of these materials result from the combination of the different magnetic features of the itinerant 3d states of the transition metal and the localized 4f electronic states of the rareearth. Some intermetallic compounds present a compensation point at which the partial magnetizations of the R and the TM sublattices have the same magnitude but opposite orientation. The temperature of the compensation point can be adjusted by controlling the rare-earth and the 3d transition metal chemical composition. Such a remarkable feature of some ferrimagnetic materials like the solid solution HoCo12-xFexB6 is a useful property wanted in the context of intense research for magneto-optical recording and magneto-transport in spintronics [1-2]. Moreover, R-TM alloys with heavy rare-earth elements are also investigated by means of optical switching experiments [2], in the context of ultrafast magnetization reversal of magnetic memories.

2

The ternary system RTM12B6 adopts the rhombohedral SrNi12B6 prototype crystal structure, space group m R 3 [3][4][5]. The 3d transition metal atoms reside on two inequivalent Wyckoff positions (18g and 18h), whereas the rare-earth element occupies only one crystal site (3a). The boron atoms are located on another 18h crystallographic position. Earlier reported studies reveal that the RCo12B6 compounds are stable for essentially all of the rareearths (with the exception of europium). The evolution of the unit-cell parameters among these compounds reflects the conventional lanthanide contraction. RCo12B6 systems order magnetically, they are ferro-(R =Y, La-Sm) or ferri-(R = Gd-Tm) magnets with a rather small mean Co moment -0.42 µB/Co in YCo12B6 -and low Curie temperature TC =134-162 K [6]. These weak intrinsic magnetic properties are ascribed to the relatively small number of Co with respect to B (factor of 2) and to the hybridization of B(p) and Co(d) electron states as a consequence of small distances between Co and B atoms (2.05 Å) [6][7][8][9]. The Co magnetic behavior has been studied in detail in both paramagnetic and magnetically ordered state. The itinerant character of the magnetism of these compounds has been established [6,] and the role of volume has been investigated by means of magnetization measurements under hydrostatic pressure up to 1 GPa [10][11][12][13]. Rather moderate pressure effect on the intrinsic magnetic properties has been observed. NMR studies [14][15][16] suggest that the Co moments on the two inequivalent crystallographic positions are different, with the Co(18h) moment being significantly larger than the Co(18g) moment. Neutron powder diffraction analyses confirmed different values of Co magnetic moments on the 18(g) and 18(h) crystal sites [12,17]. This observed difference in the Co magnetic moments is driven by the different nearest-neighbour configurations: the 18g site has 7 Co neighbours and 4 B neighbours whereas the 18h site has 9 Co and 3 B neighbours, resulting in a larger moment at the 18h site.

Following earlier reports of the presence of a spin reorientation phenomenon in HoCo12B6 [17][START_REF] Cadogan | Thompson Hyperfine Interactions (C)[END_REF], the present work is devoted to the investigation of the ferrimagnetic HoCo12-xFexB6 intermetallic compounds with Fe substitution in the range x = 0 -2 to probe the effect of Fe on the remarkable magnetic properties of such pseudo-ternary system.

Moreover, this study is motivated by the recent discovery of extreme sensitivity of the ordering direction to Fe concentration in GdCo12-xFexB6 compounds [START_REF] Lee-Hone | [END_REF][20].

Experimental techniques

Polycrystalline samples of HoCo12-xFexB6 have been synthesized by melting starting elements of at least 99.9% purity in a high frequency induction furnace under a protective argon atmosphere. In order to ensure good homogeneity, the alloy buttons were turned and remelted several times. Then, small pieces of the obtained ingots were wrapped in tantalum foil, sealed in evacuated quartz tubes and subsequently annealed at 1173 K for 21 days. The synthesized samples were characterized by chemical analysis, as well as by X-ray powder diffraction. The phase purity and the elemental composition were checked by scanning electron microscopy (SEM) in back scattered electron (BSE) contrast and energy-dispersive X-ray spectroscopy (EDS) analysis. Room temperature X-ray powder diffraction was performed on a Siemens D5000 diffractometer in reflection mode with the Bragg-Brentano geometry, using Co-Kα radiation. Least-squares refinement including all the observed Bragg reflections was applied to determine precisely the unit-cell parameters. Following the X-ray diffraction analysis, magnetic susceptibility and magnetization measurements were performed. The magnetic measurements were carried out on free powder samples in steady magnetic fields up to 10 T at temperatures ranging from 1.7 to 300 K using an extraction magnetometer. A detailed description of the extraction magnetometer can be found in Ref. 21.

The ac magnetic susceptibility was measured at a frequency of 10 kHz down to 4.2 K in a magnetic field of 3 mT.

Results and discussion

SEM and EDS microanalysis performed on the as-cast and annealed samples reveals their high chemical purity. These alloys contain a main phase HoCo12-xFexB6 with some amount of the pseudo-binary system (Co,Fe)2B. In order to minimize the quantity of this spurious phase, a slight excess of Ho was used, after which the HoCo12-xFexB6 synthesized materials were found to be mainly single phase according to the analysis of the X-ray diffraction patterns.The diffraction patterns were indexed on the basis of the rhombohedral SrNi12B6 structure; the m R 3 space group symmetry is retained for all the investigated compounds. A careful look at the diffraction patterns indicates the presence of residual traces of the (Co,Fe)2B compound as minority impurity phase. The lattice parameters of the parent compound HoCo12B6 at room temperature are a = 9.451(2) Å and c = 7.454(3) Å, in good agreement with previous results on polycrystalline samples [6,[START_REF] Cadogan | Thompson Hyperfine Interactions (C)[END_REF]. The lattice constants for the entire series of samples studied here are plotted as a function of concentration in figure 1, confirming the presence of a solid solution over the entire composition range studied. The corresponding values are summarized in table 1. It can be seen that both lattice parameters increases linearly versus Fe content. Partial substitution of Fe for Co induces a continuous increase of the unit cell volume (figure 2). The Fe ion radius is larger than Co one, that results in the observed lattice parameters and volume change. Samples with higher Fe concentration were prepared, however, they were found to contain much larger amounts of the additional (Co,Fe)2B phase.

Consequently, those samples with x > 2 were not considered further in the present study. Figure 3 shows the measurement of the ac magnetic susceptibility (χ') of HoCo11.5Fe0.5B6. Two magnetic anomalies are observed at about 73.5 K and 133 K. The latter is similar to the peak observed in YCo12B6 [22][23] and HoCo12B6 [13,17] just below the Curie temperature. This peak, also known as Hopkinson effect, is often very sharp [24]. The former indicates a magnetic phase transition of the order-order, spin reorientation type, in which a rotation of the magnetization vector with respect to the crystallographic axes occurs upon change of temperature. The values of the Curie (TC) and spin reorientation (TSR) temperatures were determined from the analysis of the temperature dependence of the ac magnetic susceptibility (χ'). TC was taken as the onset of the strong increase seen on cooling, while TSR was defined as the maximum on the χ'(T) plots observed well below TC (see figure 3). The spin reorientation transition is characterized by a change of the easy magnetization direction with temperature. The spin reorientation transition is caused by the temperature induced competition between the Ho and (Co, Fe) sublattice magnetocrystalline anisotropies which have different preferred direction. In the RCo12B6 crystal structure the Co sublattice anisotropy favors the basal plane as it has been reported for non magnetic rare-earth isotype compounds R = Y, La [12,25]. On the contrary, Ho and Nd atoms having negative secondorder Stevens coefficient have been proved to favor alignment of the magnetic moments along the crystallographic c-axis in the RCo12B6 crystal structure [17,[START_REF] Cadogan | Thompson Hyperfine Interactions (C)[END_REF]. This originates from the sign of the second order crystal-electric field parameter 0 2 A which is positive and amounts to 254 K in the RCo12B6 crystal structure [17]. This positive sign of 0 2 A is in agreement with the magnetic structure derived from neutron powder diffraction studies showing that the Ho sublattice anisotropy prefers the c-axis in HoCo12B6 compound. HoCo12B6 orders its magnetic moments close to the crystallographic c-axis at 1.5 K and undergoes an axial to basal plane spin reorientation upon heating. compound. The extra phase was consequently considered as carrying a saturated magnetic moment simplifying the correction for its ferromagnetic contribution. The impurity concentration increases from about 3 wt% up to 7 wt% for x = 0 and x = 2, respectively. The amount of impurity estimated in this manner corresponds closely to that found from X-ray diffraction analysis. The transition temperature, TC, decreases nearly linearly with the Fe concentration at a rate of -4 K/at. % Fe, as illustrated in figure 5. Figure 6 Magnetization isotherms recorded at 4 K for HoCo12-xFexB6 intermetallics are reported in figure 7. The spontaneous magnetization MS for each compound was determined as the ordinate of the crossing point of the linearly extrapolated low-and high-field portions of the isothermal magnetization curves. As can be seen from figure 7, the spontaneous magnetization is strongly dependent on Fe content. MS at 4 K exhibits a monotonic decrease with increasing Fe concentration from 3.69 µB/f.u. to 2.62 µB/f.u. as x increases from 0 to 2.

The corresponding values are given in table 2. Assuming that the Ho atom carries its free-ion moment of 10 µB oriented antiparallel to the transition metal magnetization, the average transition metal magnetic moment µTM can be derived by using MS = |µHo -12µTM |. For HoCo12B6 compound the obtained value of µTM = 0.53 µB is typical of that found in the RCo12B6 ternary system [6]. If we then write µTM as µTM = ((12-x)/12)µCo + (x/12)µFe and further assume that the Co magnetic moment µCo can be considered fixed, then we can calculate the Fe magnetic moments µFe in these compounds. The fact that the estimated Fe moment decreases with increasing Fe concentration, as shown in table 2, suggests that the a priori assumption of a constant Co magnetic moment is probably invalid. Nevertheless, it is clear that both µCo and µFe are very low in these compounds when compared to the metallic cobalt and iron.

Figure 1 :

 1 Figure 1: Lattice parameters of HoCo12-xFexB6 obtained from refinement of room temperature X-ray diffraction data.

Figure 2 :

 2 Figure 2: Room temperature cell volume as a function of Fe content in HoCo12-xFexB6 series of compounds.

Figure 3 :

 3 Figure 3: AC magnetic susceptibility (χ') for HoCo11.Fe0.5B6 compound.

Figure 4 :

 4 Figure 4: Temperature dependence of the magnetization of HoCo12-xFexB6 measured in a magnetic field of 0.1 T.

  presents the compensation, TComp, and spin reorientation, TSR, temperatures versus the Fe content in HoCo12-xFexB6 alloys. TComp increases slightly as iron is added, while TSR exhibits a more pronounced decrease with Fe content. The decrease of TSR reflects a modification of the magnetocrystalline anisotropy of these compounds upon Fe for Co substitution.

Figure 5 :

 5 Figure 5: Curie temperature TC versus x for HoCo12-xFexB6, showing the linear decline with increasing iron concentration.

Figure 6 :

 6 Figure 6: Spin reorientation temperature TSR and compensation temperature TComp versus x for HoCo12-xFexB6.

  x Fe x B 6

Figure 7 :

 7 Figure 7: Isothermal magnetization of HoCo12-xFexB6 series of compounds measured at 4 K.

Table 2 :

 2 Magnetic parameters: Curie temperature, compensation temperature, spin reorientation temperature and spontaneous magnetization for the HoCo12-xFexB6 series of compounds.

	x = 0	147	46	76	3.69	0.53	-
	x = 0.5	138	47	73.5	3.19	0.57	1.43
	x = 1	126	48	69.5	2.84	0.60	1.33
	x = 2	105	50	63	2.62	0.62	1.04

then the spontaneous magnetization increases with increasing temperature before decreasing again when approaching the Curie point. At 50 K, the magnetization increases nearly linearly with the applied magnetic field. This behavior is typical of a ferrimagnet exhibiting a compensation point near 50 K. The interpretation of the magnetization isotherms is confirmed by the analysis of the thermomagnetic curves as shown in figure 4, the magnetization of the Ho atoms being dominant below Tcomp whereas at higher temperature and up to the Curie temperature the (Co, Fe) sublattice magnetization dominates.

Conclusions

The rhombohedral crystal structure of the HoCo12-xFexB6 intermetallic compounds is preserved at least as far as x = 2. The substitution of Fe for Co leads to a lattice expansion and a progressive decrease in the Curie and spin reorientation temperatures. On the contrary, the compensation temperature is barely sensitive to the Fe content and the magnetization of the Ho and (Co, Fe) sublattices cancel out at about 50 K for all x. The spin reorientation phenomenon is interpreted as resulting from the competition between the magnetocrystalline anisotropy terms of the Ho and the transition metal sublattices. [2] A. Kirilyuk, A. V. Kimel and T. Rasing, Rev. Modern Phys. 82, 2731 (2010).

[3] K. Niihara and S. Yajima, Chem. Lett. 1, 875 (1972).

[4] W. Jung and D. Quentmeier, Z. Kristallogr. 151, 121 (1980). µ 0 H (T)


Léa Lansade
email: lea.lansade@inra.fr

Coralie Bonneau

Céline Parias

Sophie Biau

Horse's emotional state and rider safety during grooming practices, a field study

Keywords: Equus caballus, welfare, emotion, accidents, riding activity Highlights

Care given to animals, such as grooming for horses, can be a source of wellbeing when carried out correctly. However, it can cause discomfort when badly perceived lead to potentially dangerous reactions. This study aimed to describe how grooming is conducted in the field, in terms of the horse's emotional state and also rider safety. Our observations carried out on 69 horses in riding centres and sports stables show that grooming produces more negative than positive emotions. Indeed, only 5% of horses showed mutual grooming, approach or relaxed behaviour, whereas four times more horses expressed avoidance and threatening behaviours. These results have consequences for handler safety. Regarding threatening behaviours, nine incidents (a hoof or teeth passing within 10cm of the rider's body or head) were recorded. Concerning riders, 100% behaved in a risky way at least once: passing behind or under the head of the horse without keeping it in the field of view (97%) or squatting by its feet (42%). On average, riders carried out 6.7 + 0.49 dangerous behaviours per session, and sometimes up to 19. Moreover, only 7% of them wore a hard hat when preparing their horse, while the risk of concussion is just as high on foot as in the saddle. Finally, 88% of them showed posture which was risky for their backs when picking out hooves. Surprisingly, riders' experience had no effect on the parameters recorded. In particular, horse professionals were just as exposed to risky situations, did not protect their backs, and their horses showed similar levels of defensive behaviours or signs of discomfort as the less experienced riders (p>0.05). This result is undoubtedly linked to the lack of importance granted to this practice and little teaching about reading horse signals indicating comfort and discomfort. We hope that our results will make riders aware of how important grooming is for the horse's welfare as much as for their own health and safety.

Introduction

Grooming is a basic practice, but generally little training is provided for this.

Yet, it can impact both the horse's welfare and the rider's health and safety.

Regarding the welfare, since grooming is often repeated daily throughout the life of many horses (20-30 years) it can have a cumulative effect. This can result in a long-term incidence on the horse's welfare and its relationship with humans. Welfare can be defined as an individual's subjective perception of its physical and mental state regarding how it copes with its environment [START_REF] Broom | Welfare, Stress, and the Evolution of Feelings[END_REF]. It can also be viewed in terms of affective states and their balance over time [START_REF] Ahloy-Dallaire | Play and optimal welfare: Does play indicate the presence of positive affective states?[END_REF]. Thus, improving welfare not only involves reducing negative affective states, but also fostering positive states [START_REF] Boissy | Assessment of positive emotions in animals to improve their welfare[END_REF][START_REF] Fraser | Animal behaviour, animal welfare and the scientific study of affect[END_REF][START_REF] Mellor | Extending the 'Five Domains' model for animal welfare assessment to incorporate positive welfare states[END_REF]. To induce positive emotional states in animals is difficult and few methods to achieve this have been described in the literature. However, tactile contact through grooming has been reported to be successful in different species [START_REF] Nielsen | Making sense of it all: The importance of taking into account the sensory abilities of animals in their housing and management[END_REF], including horses (Feh and De Mazieres, 1993;[START_REF] Mcbride | A preliminary study on the effect of massage to reduce stress in the horse[END_REF][START_REF] Schmied | Stroking of different body regions by a human: Effects on behaviour and heart rate of dairy cows[END_REF][START_REF] Reefmann | Behavioural and physiological assessment of positive and negative emotion in sheep[END_REF]. When grooming is appreciated by the horse and regularly repeated, it can improve general welfare and lead to physiological changes such as changes in basal levels of blood oxytocin [START_REF] Lansade | Facial expression and oxytocin as possible markers of positive emotions in horses[END_REF]. However, if badly perceived by the animal, grooming can result in negative emotions [START_REF] Lansade | Facial expression and oxytocin as possible markers of positive emotions in horses[END_REF]. One way of determining how an animal perceives grooming is by observing approach and avoidance behaviours. These behaviours are indicators of positive and negative emotional valence respectively [START_REF] Mendl | An integrative and functional framework for the study of animal emotion and mood[END_REF][START_REF] Corr | Approach and Avoidance Behaviour: Multiple Systems and their Interactions[END_REF]. To date, no study investigating horses' perception of grooming in the field has been conducted. This information could play and important role in improving horse welfare.

Regarding the rider's safety, how grooming is perceived can also have an impact. In particularly, if the horse perceives grooming negatively it can gradually develop reactions and defensive behaviours which in the long-term make it dangerous to handle (review: [START_REF] Hall | Assessing equine emotional state[END_REF]. A study showed that 70% of accidents with horses result from the horse's behaviour [START_REF] Silver | Hazards of horse-riding as a popular sport[END_REF]. Handling a horse on foot can be as dangerous as riding it. A quarter of accidents involving horses that require hospital treatment take place while the rider is on foot [START_REF] Giebel | Horse riding accidents involving children[END_REF]. Furthermore, against all odds, when on foot children had significantly more severe injuries and were also twice as likely to require intensive care or surgery, and were eight times more likely to sustain a severe head injury than when riding [START_REF] Wolyncewicz | Horse-related injuries in children -unmounted injuries are more severe: A retrospective review[END_REF]. In a study conducted on 284 patients who were victims of an accident involving a horse, three deaths were recorded [START_REF] Carmichael | On and off the horse: Mechanisms and patterns of injury in mounted and unmounted equestrians[END_REF]. All of these happened while the rider was on foot (being knocked over, or kicked in the head or chest). To prevent tragedies and for riding to remain a pleasure, care should be taken when interacting with horses, during grooming especially.

Although not involving accidents, when incorrect gestures are performed repeatedly while preparing a horse there can also be long-term consequences for the rider's back. A causal link has been highlighted between back pain (concerning 75% of professional riders) and activities around horses including grooming, whereas no link has been established with riding itself [START_REF] Biau | Prevalence of back pain and its risk factors in professional horse riders[END_REF]. This back pain often becomes chronic in professional riders and can affect the length of their career (prevalence in this population: 9% of chronic neck pain, 13% of chronic thoracic spine pain and 23% of chronic low back pain). To avoid this pain, recommendations include avoiding a risky posture when carry a load (such as picking out hooves) by bending the knees when your back is inclined forward at an angle greater than 30 degrees. In this way the back can be kept straight, respecting the natural curve of the spine. However, we do not know whether riders apply this recommendation in the field.

The present study aimed to assess grooming as carried out in the field to: 1) analyse the emotional perception of horses through observing approach and avoidance behaviours, 2) quantify rider and horse behaviours or postures that could be at the root of accidents and back pain, 3)determine whether riders improve their practice with experience. The effect of horse's gender and breed was also tested.

Material and Methods

Subjects

The study investigated 69 rider-horse pairs in 12 different riding establishments in France. There were 12 mares and 57 geldings (46 horses and 23 ponies). They were divided into groups according to the rider's experience: beginners in a riding school (n=18); intermediate to advanced riders in a riding school (n=25); horse owners with an advanced level (n=9); horse professionals (n=17). The beginners were people who rode horses once a week in a riding school, and had a low level of riding (the French riding qualification "Gallop 1 to 3"). The intermediate to advanced riders rode horses once or twice a week in a riding school and had an intermediate to advanced riding level (the French riding qualification "Gallop 4 to 7"). The horse owners had their own horse and all of them had an advanced riding level of (the French riding qualification "Gallop 7"), they rode their horse several times a week. Horse professionals could be either professional riders, or professional grooms who worked with different horses every day. The pairs were independent of each other. The mean ages of horses and riders were 11.7+0.67 years and 24.31+1.75 years (mean +sem), respectively.

Video recording protocol

On arriving at a riding establishment which had previously been contacted, we asked riders who were getting ready to ride if they agreed to be filmed while they groomed their horse (brushing and picking out hooves). Each grooming session was filmed in its entirety using a digital video camera recorder (DCR-SR21E, Sony) on a tripod at a distance of 3.5m (horses were filmed in profile).

Behavioural observations

The behaviours or postures of each horse and rider were recorded by the same observer from the video footages of the whole grooming sessions (mean+sem duration: 11min40 +0.47).

Horse behaviours

The horse behavioural repertoire consisted of two behavioural categories: avoidance behaviours and approach/relaxed behaviours (Table 1). These behaviours were recorded continuously during the whole session, as described in [START_REF] Lansade | Facial expression and oxytocin as possible markers of positive emotions in horses[END_REF]. When a behaviour lasted more than three seconds without interruption, the observer noted its occurrence every three seconds.

Handler safety

The observer recorded the number of dangerous behaviours for each rider continuously: passing just behind the horse or under its neck without having the horse in their field of view, squatting beside the horse's foot, kneeling on one knee next to the horse's foot. We also recorded the number of times a potentially dangerous incident was narrowly avoided when a horse showed threatening behaviour, that is to say when the horse's hoof or teeth came within 10cm of the rider's body or head. For the ergonomic data, by using freeze frames during hoof picking we record whether the rider took a risky position for their back: bending over more than 30 degrees without bending their knees. Finally, we also recorded whether the rider was wearing a hardhat or protective jacket.

Statistical Analyses

For the horse behaviours, many individuals had zero values (between 97% and 78% zero values according to the variable). Thus, we transformed the continuous data into binary data (expressed / did not express this behaviour).

We compared the number of horses which expressed one of the behaviours mentioned above at least once between the categories of behaviours (approach/relaxed attitude vs avoidance) using Z tests. The proportion of horses which expressed these behaviours were also compared between gender and category of breeds (ponies vs horses) using Z tests and between groups of riders using the Monte Carlo method to compare multiple proportions followed by a Marascuilo Procedure for post hoc tests. For handler safety, the data were analysed in the same manner (expressed / did not express), but also as continuous data and compared between groups using Kruskal-Wallis tests (except for the number of riders kneeling, since they were 96% of zero values). The statistical analyses were performed with XLStat software (Addinsoft Software, Paris, France). The significance threshold was set at 0.05.

Ethic statement

The authors read the policy relating to animal ethics and confirm that their study complied. We only observed the horses during grooming in a field condition, and the animals underwent no specific experimental procedures for this research.

Results

Horse behaviours

There were four times more horses which expressed avoidance rather than approach/relaxed behaviours during grooming (avoidance: 15/69, approach/relaxed: 4/69, Z test for proportion z=-2.54; P=0.01). This indicates that only 5.7% of horses expressed approach/relaxed behaviours. Looking in detail at the avoidance behaviours, 12 horses were observed carrying out threatening behaviour, three moved away and two contracted their belly or back (some horses combined several behaviours). For approach/relaxed behaviours, two horses attempted to nibble the handler, two encouraged contacts and one showed a relaxed attitude. Some horses expressed avoidance behaviours up to 16 times during a single grooming session, compared to only a maximum of five times for approach/relaxed behaviours.

Gender had no effect on the number of horses expressing avoidance or approach/relaxed behaviours (avoidance: 4/12 mares vs 11/57 geldings, Z test for proportion z=0.62; P=0.54; approach/relaxed: 1/12 mares vs 3/57 geldings z=0; P=1). There were no differences between the horse and pony categories (avoidance: 5/23 ponies vs 10/46 horses, Z test for proportion z=0; P=1 approach/relaxed: 1/23 ponies vs 3/46 horses, z=0; P=1).

Handler safety

All the riders showed a behaviour considered to be dangerous at least once: 97% passed just behind the horse or under the neck without having the animal in their field of view, 42% squatted down beside the horse's foot and 4% knelt near the horse's foot. The riders carried out 6.7+0.49 (mean +sem) dangerous behaviours in one session and this figure could be as high as 19.

Regarding the threatening behaviours of horses, nine potentially dangerous incidents were observed (teeth or hoof passing within 10cm of the rider's body or head). Regarding risky postures for the back during hoof picking, 88% of riders demonstrated this. Finally, 7% of riders wore a hardhat to prepare their horse (three children in a riding centre and two horse professionals) and no one wore a protective jacket.

Experienced rider effect

Among the variables presented above, only two differed significantly according to the rider's experience. The other, including the length of the session, never differed significantly between groups (p>0.05).

Regarding horse behaviours, only the percentage of horses displaying "encouraging contact" differed significantly between groups (Chi2=13.9; p=0.01): this was only observed in privately-owed horses (Fig. 1). However, given the fact that this behaviour was expressed at a very low level (two out of the nine privately-owned horses, and none in the other categories) extreme caution should be taken in interpreting this difference.

Regarding handler safety, the "percentage of riders squatting beside the horse's foot" differed between groups (Fig. 2). Fewer beginner riders than intermediate to advanced riders squatted (Chi2 = 8.09; p=0.04). No other percentage of riders differed between groups. The Kruskal Wallis tests on the number of dangerous behaviours carried out per rider gave no significant difference between groups for any variable.

Discussion

This study highlights that in the sport stables and riding schools that we visited, only 5% of the horses observed expressed mutual grooming, approach or relaxed behaviour, whereas avoidance and threatening behaviours were expressed by four times more horses. When considering the former as indicators of positive emotional valence and the latter as indicators of negative emotional valence [START_REF] Feh | Grooming at a preferred site reduces heart rate in horses[END_REF][START_REF] Mendl | An integrative and functional framework for the study of animal emotion and mood[END_REF], it can be concluded that in the field grooming induces less positive than negative emotional states. These results are not linked to a bias in the observation method because in a previous study using the same method, we observed that 100% of the horses expressed an approach response during gentle grooming which was adapted to the horse's reactions [START_REF] Lansade | Facial expression and oxytocin as possible markers of positive emotions in horses[END_REF]. Our results also showed that the proportion of horses that expressed avoidance or approach behaviours were independent of their gender or breed. This could suggest that these behaviours were less due to the horses' characteristics, than to the way they were groomed.

These results are far from insignificant for the horse or for the rider. For the horse, the fact that grooming sessions can be repeated daily throughout its whole life (20-30 years) could have a cumulative effect which when negatively perceived would be deleterious to its welfare [START_REF] Boissy | Assessment of positive emotions in animals to improve their welfare[END_REF]. Indeed, as little as two weeks of daily grooming has been reported to modify a horse's physiology, with a change in basal blood oxytocin level [START_REF] Lansade | Facial expression and oxytocin as possible markers of positive emotions in horses[END_REF]).

It has also been shown that the way a horse perceives handling sessions can have a long-term impact on its relationship with humans and how it perceives and reacts to subsequent situations involving people [START_REF] Sankey | Positive interactions lead to lasting positive memories in horses, Equus caballus[END_REF][START_REF] Lansade | Facial expression and oxytocin as possible markers of positive emotions in horses[END_REF].

Concerning rider safety the way a horse perceives humans can influenced the level of risk during handling [START_REF] Hall | Assessing equine emotional state[END_REF], and this is supported by our results. Indeed, regarding the threatening behaviours demonstrated by the horses, nine potentially dangerous incidents were observed (teeth or a hoof passing within 10cm of the rider's body or head). The riders often did not see what had happened, because the horse was not in their field of vision when the incident occurred. Fortunately, the incidents observed in our study did not lead to injury. However, when these data are compared with the rate and severity of accidents with riders on foot, which are much higher than for riders in the saddle, it can be seen that it is not always the case [START_REF] Wolyncewicz | Horse-related injuries in children -unmounted injuries are more severe: A retrospective review[END_REF]. These results are also in line with research that has shown that 70% of accidents would be linked to horses' reactions [START_REF] Silver | Hazards of horse-riding as a popular sport[END_REF].

In addition to horses' potentially dangerous reactions, this study also showed that 100% of riders demonstrated behaviours considered as risky, such as squatting beside the horse's foot. Moreover, only 7% of riders wore a hardhat when preparing their horse and none of them wore a safety jacket, while the risk of concussion is at least as high on foot as in the saddle [START_REF] Wolyncewicz | Horse-related injuries in children -unmounted injuries are more severe: A retrospective review[END_REF]. Finally, 88% of riders demonstrated a risky posture for their back when picking out hooves. This could explain why riders' back problems are linked more to grooming than to riding [START_REF] Biau | Prevalence of back pain and its risk factors in professional horse riders[END_REF]. These figures underline that grooming practised in the field can cause discomfort for the horse, and is also a potential source of back problems and accidents for riders.

Surprisingly, almost none of the parameters considered in this study differed between the levels of rider experience. In particular, the horse professionals demonstrated just as many potentially dangerous behaviours and took no more care of their backs, and their horses showed no fewer defensive behaviours or signs of discomfort than the less experienced riders. This is in line with studies that have shown that horse professionals are as or more at risk of accidents than amateurs [START_REF] Hausberger | A review of the humanhorse relationship[END_REF]. This result is probably linked to the lack of importance given to grooming and learning to groom. However, a limitation of this comparison should be noted due to the relative low number of subjects in the "owners" group (n=9).

Nevertheless, it would be relatively simple to improve grooming practices to induce positive behaviours. In Feh and de Mazières' study (1993) many positive behaviours were induced when the horse was massaged in its preferred zones. To find the horse's preferred zones it is simply a question of being attentive to approach and avoidance behaviours and also facial expressions which constitute a particularly sensitive way to detect the horse's emotional state [START_REF] Hintze | Are Eyes a Mirror of the Soul? What Eye Wrinkles Reveal about a Horse's Emotional State[END_REF][START_REF] Lansade | Facial expression and oxytocin as possible markers of positive emotions in horses[END_REF]. An eyebrow that is Improving grooming practices could have numerous benefits on welfare and rider safety as discussed above, but also on the efficiency of the riding session that generally follows the grooming. Indeed, there is a huge amount of literature reporting the effects of emotions on learning abilities (example in horses: [START_REF] Christensen | Does learning performance in horses relate to fearfulness, baseline stress hormone, and social rank?[END_REF][START_REF] Valenchon | Stress affects instrumental learning based on positive or negative reinforcement in interaction with personality in domestic horses[END_REF][START_REF] Fortin | Emotional State and Personality Influence Cognitive Flexibility in Horses (Equus caballus)[END_REF][START_REF] Hall | Assessing equine emotional state[END_REF]. Thus, it is highly probable that the emotions induced during grooming could impact the subsequent training session, either by increasing or decreasing its effectiveness.

In conclusion, this study shows that in general riders pay little attention to their horse's threats and signs of discomfort, and thus sometimes put themselves in danger during grooming. Yet, it would be easy to enhance this practice to improve the horse's welfare and rider safety simply by observing the horse's behaviour and facial expressions and adapting the brushstrokes accordingly. Regarding the number and severity of accidents on foot linked to horses and the high prevalence of back pain, raising riders' awareness to grooming best practices in the field seems essential. References correcting the English manuscript as well as the riding establishments which allowed us to carry out the work on their premises. IFCE (French Horse and Riding Institute) funded this experiment. This funding source had no role in study design, data collection or analysis, or preparation or submission of the manuscript Table 1. Behavioural parameters recorded during grooming

  raised, low neck carriage, eyes half closed and lips extended are signs of positive emotional state during grooming, and should encourage the handler to continue brushing that area. By contrast, a raised neck, eyes wide open and even slight tensing of the corner of the mouth indicate a negative emotional state and should lead the person to change their way of brushing. Even worse, a grimace of pain, as describe by Dalla Costa (2014) should also alert the handler.

Figure captions Figure 1 .

 captions1 Figure captions

Acknowledgements

We would like to thank Jean-Marie-Yvon for his assistance during the experiment, Sue Edrich from the translation agency Interconnect for