Evaluation of the ‘maximum price paid’ as an index of motivational strength for farmed silver foxes (Vulpes vulpes)

Abstract

To measure farmed foxes' motivations for full, naturalistic social contact, we constructed an apparatus where they could perform an operant to access stimuli, but then leave freely and thence determine their own bout lengths. Motivational measures based on demand curves can be invalid in such set-ups, and we therefore sought to validate the measure 'maximum price paid'. This was achieved by measuring six silver fox males' maximum operant responding for access or proximity to three resources differing in biological significance: food, vixens in oestrus and males. We predicted that if valid, maximum price paid would be highest for food and vixens. Maximum price were 970 AE 399 (S.E.) for food, 677 AE 173 (S.E.) for vixens and 389 AE 101 (S.E.) for other males (P < 0.05). In contrast, our complementary measures of motivation -price elasticity, expenditure and consumer surplus -did not differentiate between the resources, and ranked them in different orders (albeit not significantly). This was because the foxes rescheduled their behaviour with increasing costs, decreasing bout number while increasing bout length, to different extents with the three resources. Additional findings showed that all subjects 'overpaid', performing the operant response more than was required. This increased as the costs increased, perhaps due to increasing 'time outs' on the time-restricted schedule (DRH) as the task got harder. However, the overpayment was also highest when males were the resource, suggesting that operant responding was slowest and least efficient when working for less-valued resources. The resources present also affected how the foxes used the rest of the apparatus and influenced their behaviour; subjects staying more in the operant compartment when the resource was social (especially a female), but retreating to a distant compartment when it was food. While proximity to oestrous vixens elicited higher levels of tail wagging and only low levels of pacing, indicating a positive motivation, proximity to males elicited relatively high levels of pacing plus agonistic gaping, suggesting that the motives for seeking contact with males related to aggression. Thus, although our operant set-up reveals a drive to approach other males, the possible aggressive motives suggest that this sort of social contact would not necessarily improve their welfare in a traditional housing system. Overall, these results help improve the design and interpretation of preference tests, and confirm maximum price paid as a useful motivational measure for farmed foxes. #

Responses of farmed silver foxes (Vulpes vulpes) to excessive food availability: Implications for using food as a yardstick resource in motivation tests

“…This suggested that if food is offered ad libitum, foxes might have periods of gorging and of relative fast, a factor potentially adding great day-to-day variability to measures of motivation. In contrast, when we offered food in more limited quantities, the foxes' value of food was closer to our predictions and day-to-day food-use was also more consistent (Hovland et al, 2006). If silver foxes are sensitive to the amount of food provided and this leads to periods where subjects stop eating for more than the 'cut off' period (e.g.…”

“…To examine farmed foxes motivational strength our research group developed an operant apparatus where foxes could work (by pulling a loop) for access to various resources (Hovland, 2005). Our main measure of motivation was the maximum price paid, which was the highest number of pulls foxes were willing to pay before giving up access for 24 h. Although this apparatus ultimately worked well (Hovland et al, 2006), much pilot work was needed to refine the methodology. Our refinement and validation of the apparatus is described elsewhere (Hovland, 2005;Hovland et al, 2006), but here we examine how the presentation of the useful yardstick 'food' could affect how it is used by foxes and perhaps even valued.…”

Animal economics: assessing the motivation of female laboratory rabbits to reach a platform, social contact and food

“…Warburton & Mason (2003) similarly found that mink, Mustela vison, worked for access to limited social contact with neighbours, despite being naturally a solitary and territorial species. Hovland et al (2006) in their study of foxes, Vulpes vulpes, found that males would work hard for access to both male and female conspecifics; however, whereas female stimulus animals attracted affiliative responses such as tail wagging, male stimulus animals attracted threat displays. Both these studies suggest that some stimuli are not positive or enriching additions to the standard cage, even if access for them is worked for.…”

Individual differences in stereotypic behaviour predict individual differences in the nature and degree of enrichment use in caged American mink

“…Maximum price paid (MPP), used to assess motivational strength, is obtained by imposing a series of costs on access to a resource and recording the maximum cost an animal is willing to pay (Hovland et al, 2006;Kirkden et al, 2003). Because individual differences in MPP for a given resource may also reflect non-motivational factors (e.g.…”