Publications on AMI sensors

This is a short list of scientific publications in which I have used AMI sensors. AMI stands for animal material interactions. AMI sensors can take various shapes and forms. In some way or other AMI sensors record the amount of interaction pigs have with enrichment materials for pigs. Mostly this concerns hanging toys like chains and ropes with or without suspended materials like pieces of wood. Below the list you can also find the abstracts. So far the use of AMI sensors is (mainly) restricted to application for scientific purposes, eg to measure the value of (different aspects of) enrichment materials (directly or indirectly), the effect of tail-biting ointments, and abnormal and/or sickness behaviour. A blog post on AMI sensors and the future of pig farming can be found here.


To validate (further) a semantic model called RICHPIG, which was designed to assess enrichment materials for pigs, a study was conducted to examine the importance of three assessment criteria, namely destructibility, hygiene and sound. These material properties were studied using a specially constructed object consisting of a piece of sisal rope, metal wire and three fixed chain links hanging in the pens. The object was considered to be not destructible (ND), hygienic (HY) and not making sound (NS). After a habituation period of 18 h treatments were applied in that the object was (or was not) made destructible with a partial cut in the rope (DE) and/or was soiled with excreta (not hygienic, NH) and/or was allowed to make a tinkling sound by releasing the chain links (SO). The three treatments were applied in a 2 × 2 × 2 factorial design on a commercial farm in seven replicates using seven different units containing eight pens per unit. At five moments in time, ranging from 18 h before until 1 h after treatment, a range of behaviours was recorded including the frequency-related parameter AMI (animal–material interactions) and four intensity-related parameters. Repeated measures ANOVA’s showed significant effects of time and hygiene as well as interactions between time and hygiene, between time and destructibility and between destructibility and sound. Soiling (NH) significantly decreased, and destructibility (DE) significantly increased attractiveness, while sound (SO) was not significant. Only moderate correlations between AMI and the four intensity-related parameters were found (median r = 0.41, all P < 0.05), indicating that frequency-related parameters alone may not suffice to determine behavioural importance for animal welfare.

This study showed that it is in principle possible to study material properties independent of material type and that it is in principle possible to measure behavioural intensities on a commercial farm. Furthermore, the finding that hygiene and destructibility were more important for pigs than tinkling sounds provided preliminary support for the RICHPIG model.

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 1a 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 1a) 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 × 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.

Tail biting is a most serious welfare problem in pigs raised for slaughter. In instances of an outbreak of tail biting, scientists have recommended that farmers take measures such as removal of affected animals, provision of enrichment materials and application of repellents to the pigs’ tails. However, no scientific study has ever confirmed the efficacy of any of these suggestions in counteracting an ongoing outbreak. Here, the efficacy of two repellent ointments, Dippel’s oil and Stockholm tar, were examined in a tail-chew test. For this, a novel piece of nylon rope was used as a tail model to measure biting behaviour semi-automatically in 24 single-sex groups of growing pigs (total 264 pigs). Repeated measures analysis showed no effect of time, gender or unit (12 pens per unit), but a highly significant effect of treatment, in that both Stockholm tar and Dippel’s oil significantly reduced rope manipulation compared to controls. These results suggest that Stockholm tar and Dippel’s oil may be effective in reducing tail biting. The approach taken may be valuable in further testing of strategies to reduce tail biting and improving pig welfare.

Injurious behaviours in pigs may involve persistent or forceful biting in specific body parts and may result in wounds of the pigs’ tails, ears, flanks and legs. Such behaviours, which may lead to progressive tissue damage, are difficult to counteract.
On a commercial farm 22 groups of pigs with wounds on flanks (n = 16) and tails (n = 6) were matched with 22 control groups without wounds. All groups were provided with a novel rope, applied as a ‘tail chew test’. Interaction with the rope was recorded semi-automatically about 45 and 120 minutes after introduction of the rope. Statistical analysis showed significant decrease of interest in the rope over time and significantly elevated interest in the ropes in pens containing wounded animals (median number of pulls per minute in control pens, flank-biting pens and tail-biting pens were 7.8a, 10.2b and 14.3b respectively, where superscripts indicate significance levels (P < 0.001).
These results suggest that flank biting and tail biting increase exploration and destructibility in pigs. The approach taken is valuable in further understanding strategies to reduce injurious behaviours in pigs and improving pig welfare, e.g. by providing enrichment materials.

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