Motivation for social contact in horses measured by operant conditioning

doi:10.1016/j.applanim.2011.04.007

Applied Animal Behaviour Science

Volume 132, Issues 3–4, July 2011, Pages 131-137

https://doi.org/10.1016/j.applanim.2011.04.007 Get rights and content

Abstract

Although horses are social animals they are often housed individually with limited social contact to other horses and this may compromise their welfare. The present study included eight young female horses and investigated the strength of motivation for access to full social contact, head contact and muzzle contact, respectively, to a familiar companion horse. Horses were housed individually next to their companion horse and separations between pens prevented physical contact. During daily test sessions horses were brought to a test area where they could access an arena allowing social contact. Arena access during 3 min was given after completion of a predetermined number of responses on a panel. Fixed ratios (FR) of 8, 16, 24, 32 and 40 responses per arena access were applied in a random order, one per daily test session, within each test week (Monday to Friday), and the number of rewards per daily test session was recorded. All horses could access all three types of social contact in a cross-over design, and an empty arena was used as control. Motivational strength was assessed using elasticity of demand functions, which were estimated based on the number of rewards earned and FR. Elasticities of demand for the three types of social contact were low (−0.20), and not significantly different, although increasing FR still resulted in a decrease in rewards obtained for all three types of social contact (P < 0.001). Across FR-levels horses earned more rewards for social contact than for an empty arena, as shown by much higher intercept values (2.51 vs. 0.99; P < 0.001). However, the elasticity of demand for infrequent access to an empty arena (−0.08) was lower than for social contact (P < 0.01) and not significantly different from zero (P = 0.07). Horses performed more social behaviour the lesser the restriction on social contact (full > head > muzzle). However, the finding that horses showed a similar and high motivation for all three types of social contact suggests that they are valued equally highly in a situation where the alternative is no social contact.

Introduction

Domestic animals are frequently subjected to varying degrees of parental or social deprivation, but the extent to which this reduces welfare depends on the natural social structure of the species concerned. The isolation of young or adolescent primates typically produces long-term and serious physiological and behavioural changes indicative of stress and reduced coping abilities (Olsson and Westlund, 2007). In contrast, the effects of social isolation on rodents are more variable (Krohn et al., 2006, Olsson and Westlund, 2007). Maternal deprivation has especially profound effects on stress susceptibility and also increases the likelihood that the young of many species will develop abnormal behaviour (Latham and Mason, 2008). However, these effects can sometimes be ameliorated by social buffering, if young animals are kept with other familiar companions (Newberry and Swanson, 2008). The degree and nature of the social conditions experienced by young mammals can thus have both short and long-term effects on welfare.

Despite a wealth of information on the effects of social isolation in primates and rodents, relatively little is known about horses. Although horses are social animals they are often weaned early and then housed individually with limited social contact to other horses. There are strong indications that this may compromise their welfare. For instance, young individually housed horses performed more stress-related behaviours and spent less time eating than pair-housed controls (Visser et al., 2008). Furthermore, when grouped on pasture the social interactions of young horses previously housed individually were more aggressive than those of young horses previously group housed (Christensen et al., 2002).

Lack of social contact is also one cause of development of abnormal behaviour in stabled horses (Nicol, 1999, Waters et al., 2002, Visser et al., 2008). The stereotypic behaviour ‘weaving’ is especially sensitive to the degree of social contact provided (McAfee et al., 2002) and the performance of this behaviour can be reduced by allowing stabled horses increased visual contact with neighbouring conspecifics, or by providing them with mirrors or images of other horses (Mills and Davenport, 2002, Mills and Riezebos, 2005). Thus, even limited social contact may improve the welfare of stabled horses.

The main reason for housing horses individually is to avoid fights and injuries. However, the risk of fights in group housing may be more related to competition for limited resources such as space and access to feed as suggested by Jørgensen et al. (2008). Furthermore, physical contact between neighbouring individually housed horses may have beneficial effects while the risk of injury is limited. In order to weight the advantages of social contact against the risk of injury we need to know the strength of horses’ motivation for various degrees of social contact ranging from full social contact to limited contact. Elasticity of demand functions may be used to assess motivational strength. When generating demand functions an increasing cost is placed on access to perform the behaviour (the reward). Performing an operant task represents the cost and typically the ratio of operant responses per reward is held fixed (fixed ratio (FR)) within test session, but is changed between sessions. The demand function describes the change in number of rewards earned as a function of the cost (FR). The elasticity of a demand function is defined as the percent change in rewards earned divided by the percent change in cost. Generally, the lower the elasticity the higher the motivation, i.e. the lower the elasticity the more the animal increase the response rate as cost increases (Hursh, 1980, Matthews and Ladewig, 1994, Jensen and Pedersen, 2008). Comparing demand functions it was shown that dairy calves were more motivated for full social contact compared to head contact only (Holm et al., 2002), but similar studies in horses have not been carried out.

The aim of the present study was to assess the motivation of horses for three types of social contact: full contact, head contact and muzzle contact. We hypothesised that horses are most motivated for full contact followed by head and muzzle contact.

Section snippets

Animals, housing and management

Twelve 18-month old Danish Warm-blood fillies bred and raised at the same stud were used. All animals had been group housed in one larger group prior to the experimental period. During the first two weeks after arrival at the experimental station all 12 horses were kept in one group in a large paddock. Nearest neighbour observations (Christensen et al., 2002) were performed on three consecutive days of the last week and groups of three individuals that were frequently observed near each other

The effect of type of social contact

The type of social contact offered in the arena did not affect the demand for arena access and the following common demand function could be fitted in log–log coordinates (y = 2.55 − 0.20x (SE_intercept = 0.15, SE_slope = 0.034), Fig. 3). The slope of this demand function was negative and significantly different from zero (F_1,141 = 32.33; P < 0.001).

The duration of the test session decreased with increasing FR (F_1,118 = 11.96; P < 0.01) from 48 min at FR8 to 42 min at FR40. The common function describing the

Discussion

Contrary to expectation, we did not find a higher demand for full social contact compared with either head contact or muzzle contact. However, as expected, the horses were more reluctant to work for access to an empty arena than for social contact.

The results show that young female horses will work for access to physical social contact during short daily test sessions if their routine daily access to social contact in the home environment is limited to visual, olfactory and auditory contact.

Acknowledgements

This experiment was funded by The Danish Agency for Science, Technology and Innovation. Thanks to Viegaard Stud for lending us the horses. Thanks to Anton Jensen, Henrik Andersen, Helle Ammitzbøl and Irith Madsen (all Aarhus University) for handling the horses, to Erik L. Decker, Aarhus University, for constructing the test apparatus and assistance with data editing, to Erik Jørgensen, Aarhus University, for statistical advice, and to Janne Winther Christensen, Aarhus University, for valuable

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¹: Present address: AgroTech A/S, Institute for Agro Technology and Food Innovation, Agro Food Park, DK-8200 Aarhus N, Denmark.

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Motivation for social contact in horses measured by operant conditioning

Abstract

Introduction

Section snippets

Animals, housing and management

The effect of type of social contact

Discussion

Acknowledgements

Appl. Anim. Behav. Sci.

Appl. Anim. Behav. Sci.

Appl. Anim. Behav. Sci.

Appl. Anim. Behav. Sci.

Appl. Anim. Behav. Sci.

Anim. Behav.

Appl. Anim. Behav. Sci.

Appl. Anim. Behav. Sci.

Appl. Anim. Behav. Sci.

Anim. Behav.