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Article
The type of operant response affects the slope of the demand curve for food in mink.

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Abstract

The behavioural priorities of farm animals may be quantified by demand functions generated by use of operant conditioning techniques. However, there are several aspects of this method that still need to be investigated in more detail. The aim of this study was to investigate the effect of operant response type on the demand function for food in mink. The responses examined were pressing a lever and pulling a chain. The experiment was conducted with eight mature female mink. During each of two periods, the mink were tested in four replicates of successively increasing fixed ratio (FR)values (4, 8, 16, 25, 60, 80 and 100). The rewards were available for 24 h per day and each reward consisted of 0.5 of food. Half of the animals worked on the lever in the first period and on the chain in the second period, the other half of the animals vice versa. The mink were weighed regularly throughout the experiment. The behaviour of the mink was video recorded continuously for 24 h on the days when they were working on FIR levels 4, 40 and 100. The number of rewards and thereby the amount of food earned decreased as the FR-values increased for all animals. The demand curve for food obtained by chain pulling was steeper than the demand curve obtained by lever pressing (P < 0.001). The results show that the response type can influence the slope of demand functions. One reason for the difference in slopes of the demand curves could be that the unit price paid on the chain and on the lever at a given FR-value was not the same, even though the minimum force required was 35-40 g for both types of response. The slope of the demand curve for food in mink was much steeper than previously found in mice, rats, pigs and hens. This is most likely due to the combination of high FR-values and small rewards in relation to the foraging strategy in mink. High levels of stereotypies were related to high workloads on the chain. The mink had a more restricted food intake and a higher level of s


Article
Social isolation affects the motivation to work for food and straw in pigs as measured by operant conditioning techniques.

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The aim of the study was to investigate if the presence or absence of a companion pig (pig in an adjoining pen during testing) systematically influenced the demand function for food or straw in growing pigs. The experiment was carried out in two phases. In one phase, the demand for food was tested (n = 10) and in another phase the demand for straw was tested (n = 10). A different set of test pigs was used in each phase. Pigs were tested daily in an experimental room consisting of two identical twin-pens (one for the test pig and one for the companion pig (if present)). The test pigs worked for a resource by pressing a panel on a fixed ratio (FR) schedule, while the companion pig (if present) was simply given the same amount of the resource each time the test pig earned one, The reward size was either 26 g of food or 500 g of straw. The experimental set-up was a cross-over design with all pigs working on both treatments (isolation/companion). Each period consisted of three identical runs of 4 FR-levels (food experiment: FIR 8, 20, 40, 60 and straw experiment: FR 2, 5, 10, 15). The results showed a steeper slope of the demand function when pigs were tested in isolation compared to when they were tested with a companion pig (slope of demand function: -0.11 +/- 0.01 versus -0.07 +/- 0.01) (F-1.58 = 4.2; P = 0.04). The slope of the demand function for straw was unaffected by social isolation, whereas the intensity y-intercept) of the demand function was higher when pigs were tested with a companion compared to in isolation (intercept of the demand function: 3.2 +/- 0.15 versus 3.0 +/- 0.15) (F-1.26 = 4.42; P = 0.04). The use of the straw was affected by FR level in that the time spent with each reward before a new reward was obtained increased with increasing FR (F-1.177 = 165 P < 0.0001). Similarly, the percentage of time during which the pigs interacted with the straw was higher when they were tested with a companion pig compared it) when the were tested in isol


Article
Social isolation affects the motivation to work for food and straw in pigs as measured by operant conditioning techniques.

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