Differing results for motivation tests and measures of resource use: the value of environmental enrichment to gestating sows housed in stalls.

摘要

Sows are often housed in barren stalls during breeding and/or gestation. Environmental enrichment may improve sow welfare; however, the value of specific enrichments to sows is largely unknown. Our aim was to compare the motivation of gestating sows (32, n=8/treatment) housed in stalls (2.1 m x 0.6 m), and fed at commercial levels, for access to the following enrichments: compost in a trough (2.3 kg) or straw in a rack (0.5 kg), in comparison to a positive (additional food, 0.9 kg) and a negative (empty trough) control. Sows were trained to press an operant panel on an ascending series of fixed ratio (FR) schedules for one of the four resources, which were visible during testing. The schedule was increased by 50% each day following completion of FR 10 (FR 1, 10, 15, 23, 35, 53, 80, 120, 180, 270, 405, 608, and 912) and a maximum of one reward was allowed per day. The highest schedule completed (i.e., highest price paid) indicated motivational strength. Sows were given 1 h each day to press the operant panel and a maximum of 23 h resource access in the stall. Measures of resource use were also obtained. Sows showed a lower latency to press the operant panel (food: 11.2+or-7.1 s; compost: 5.0+or-1.6 s; trough: 245.6+or-216.6 s) and higher operant responding (food: 462.9+or-91.9 presses; compost: 196.9+or-37.0 presses; trough: 59.9+or-12.0 presses), indicating higher motivation, for access to food and compost compared to an empty trough (all comparisons, P<0.05). There were no differences between straw and an empty trough (straw: latency, 332.9+or-263.5 s; operant responding, 105.1+or-33.4 presses; both, P>0.05). Behavior prior to testing (which may indicate anticipation) was not affected by treatment. Sows spent a higher percentage of time interacting with straw upon resource access (straw: 18.0+or-3.8%; food: 3.3+or-0.4%; compost: 5.8+or-1.1%; trough: 2.8+or-1.5%; all comparisons, P<0.05). Compost (as indicated by operant responding) and straw (as indicated by resource use) are valued by sows housed in barren stalls and their provision should be considered to improve welfare. This study highlights the importance of investigating both resource use and motivation measures, as these methods demonstrated contrasting findings. Aspects of enrichment provision, such as method, quantity, and timing, may play a key role in determining its value, and thus effectiveness, as a means to improve sow welfare in barren systems.