Assessing object recognition memory in the domestic pig

Amanda Kristyne Gifford

This thesis was undertaken to examine the performance of pigs in a spontaneous object recognition test, whereby preference for a novel stimulus instead of a previously experienced stimulus is a measure of recognition of the familiar stimulus. Knowledge of the robustness of a pig’s memory for objects and the factors affecting it could be useful in a variety of contexts. I first review what is known about the cognitive abilities of pigs and why this might be important from an animal welfare as well as an animal production standpoint. I then focus on recognition memory, including how it is tested in various species and what is known of the neural mechanisms mediating recognition memory. Next I discuss novelty preference as a specific way to assess recognition, and describe two experiments using the spontaneous object recognition test to investigate object recognition memory in pigs. In the first experiment, I hypothesized that object recognition memory in the pig would be mediated by length of initial exposure to the object, and the delay between initial exposure and re-exposure. I predicted that increasing the exposure time would result in novelty preference at longer delays, and that novelty preference would decrease as delay increased. Pigs were exposed to two sample objects for 10 minutes and 2 days, respectively, and tested at delays of 1 hour, 3 hours, 5 days, and 6 days. Pigs did not demonstrate recognition of the 10-minute sample object at any delay, as indicated by a lack of preference for the novel object. Pigs demonstrated no recognition of the 2-day sample object at the 1-hour delay, but did at the 3-hour and 5-day delay, and novelty preference increased from the 1-hour delay to the 5-day delay for the 2-day sample object. In the second experiment, I refined the test methodology and further tested the prediction of decreased novelty preference over increasing delays using a single short (5-minute) exposure time and separate groups for time delays of 1 hour, 24 hours, and 5 days. Pigs did not demonstrate a novelty preference at any delay. Overall, the results indicate a need to reduce within treatment variability in responding and to establish a stable novelty preference before testing. They also cast doubt on the interpretation that a lack of novelty preference indicates failure to recognize the sample object.

Assessing object recognition memory in the domestic pig

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