New research from the Animal Sciences Group of Wageningen University in the
Netherlands studied the effects of light intensity (illumination) and object
size on the pigs' ability to distinguish visual signals.
In most West European countries pigs are housed indoors under low-light
conditions. While former Dutch National legislation for pigs required 12 lx (lux) for 8 hours per
day, EU legislation requires 40 lx, so pigs should be able to distinguish small
objects and subtle visual signals.
However, limited scientific evidence
exists about the effects of light intensity (illumination) and object size on
the pigs' ability to distinguish visual cues. Wageningen studied these two
effects using operant conditioning with a Landolt-C
symbol as shape discriminator. Four Landolt-C symbols with different sizes
were tested under 8 different illuminant levels (0.5, 3, 6, 12, 20, 30, 40 and
Following a 4-week training period,
20 female 4-month-old pigs were tested in two batches and the numbers of
correct, hesitant and incorrect choices were recorded. Reduced illumination
significantly increased the number of incorrect choices. Symbol size also had a
significant effect; pigs made more mistakes with the two smaller symbols
compared to the bigger symbols. Furthermore, pigs hesitated less with the
smallest symbol compared to the other ones. Visual acuity (ability to
distinguish details and shapes) varied from 0.001 to 0.03 and pigs failed to
discriminate visual cues below 20 mm.
Results indicate that the detail of the visual cue (symbol
size) has a more pronounced effect on the pigs' ability to distinguish visual
cues, compared to the illuminant level.
Sciences Group WUR
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