Calling by domestic piglets:
Honest signalling and animal welfare
D.M. Weary and D. Fraser
Agriculture and Agri-Food
Canada, Ottawa, Canada
We performed three manipulations
on piglets to determine if differences in calling can indicate differences
in need. In all cases, the aim was to manipulate the piglet's need
for the sow's attention. In the first manipulation we selected a
"thriving" piglet (i.e. the piglet with the heaviest weight and most rapid
weight gain) and a "non-thriving" one (lightest and slowest weight gain)
from each of 15 litters. The two piglets were removed from the sow
and litter and recorded for 13 min in separate isolated enclosures.
For the second manipulation, two piglets of intermediate weight and weight
gain were selected from 15 litters, and were removed from the sow during
nursing. The "unfed" piglet was removed just before the milk ejection
and the "fed" one just after receiving milk. Both were recorded as
in the first manipulation. In the third manipulation, we again selected
two similar piglets from each litter but recorded them in different enclosures:
a "warm" enclosure at 30 C, and a "cool" enclosure at 13 C. "Non-thriving"
and "unfed" and "cool" piglets called more,
used more high frequency
calls, used longer calls, and used calls that rose more in frequency than
their "thriving", "fed" and "warm" litter-mates. We argue that
if a piglet's calls provide reliable information about their need for the
sow's resources, then this calling behaviour can be used as a measure of
its welfare. Not all animal signals will be useful in evaluating animal
welfare: only "honest" signals of need. These results are consistent
with theoretical models of honest signalling.