Novel object test can detect marginal differences in environmental enrichment in pigs

In search for a test measuring positive emotions in pigs for application in on-farm welfare auditing, three small experiments were conducted to examine the sensitivity of a novel object test designed to measure the pigs' (residual) need/motivation for enrichment. In the experiments the interactions with a novel piece of rope were measured at pen level using a so-called AMI sensor (AMI: animal-material interactions). Measurements were taken at several points in time over a 1-2 h period in order to test the effects of marginal enrichments, namely the provision of a jerrycan canister (Experiments I a and 1b) and the provision of some sawdust and/or removal of the metal chain (Experiment 2). The first experiment was replicated in, respectively, 8 and 15 matched pairs of pens with groups of about 11 growing pigs per pen. A jerrycan was provided in one pen of each pair as of the day before the novel object test. In the first replicate (Experiment I a) only a main effect of time was found in that AMI decreased over time. In the second replicate (Experiment 1b) the provision of the jerrycan significantly reduced AMI. A sign test also confirmed this effect for the data in the first replicate. The recent provision of a jerrycan, therefore, marginally, but statistically significantly, reduced AMI in the novel object test. Experiment 2 was a 2 x 2 factorially designed study conducted in 40 pens containing groups of 24 weaned piglets. Factors were sawdust provision and chain removal. The four treatment combinations were applied as of 45 min before the test. In addition to a main effect of time, it was found that AMI significantly increased when the chain had been removed (P = 0.006), and that the provision of sawdust tended to depress AMI at 10 min, while tending to enhance AMI at 30 min (interaction between time and sawdust provision: P = 0.097). The results indicate that the novel object test may be used to detect relatively minor differences in environmental enrichment. (c) 2007 Elsevier B.V. All rights reserved.