Preference and Motivation
Testing as They Relate to Animal
Welfare
Camie Heleski
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Seems like the ideal way to let the animal
“tell” us which management scenario they
prefer
But, does the animal truly choose the option
that maximizes long term fitness
(e.g. does child given choice of balanced
meal vs. candy bar make the “good”
choice?)
Preference tests
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tests that require animals to choose between
two or more different options or
environments
– e.g. hens given options of different types of
cages
– hens given option of dust bath or no dust bath
– horses given option of treadmill exercise or
stall
Preference tests
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Used since early 1970’s (though anecdotally
much longer than that)
Have been used to establish animal
preferences for: housing options
(temperature, illumination, preferred
bedding), loading ramps, nest boxes, etc.
Motivation tests
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How hard will an animal work to gain
access to its preferred option
How hard will an animal work to avoid its
less favored option
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Animals’ preferences may vary with time of
day, age & experience of animal
Tests sometimes confuse familiarity with
preference
Animals may not be capable of
distinguishing short term benefits of small
magnitude from long term benefits of large
magnitude
To use preference testing to
answer questions about animal
welfare...
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1. We must ensure that experiments
adequately reflect the animals’ preferences
2. We must establish how strongly
motivated the animal is
3. We must consider that preferences will
not always correlate with enhanced welfare.
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Fundamental to the premise of using
preference testing to evaluate animal
welfare is the assumption that animals make
choices that are in their best interests.
Brambell Committee, 1965
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First proposed “asking” the animals’
opinions about their environmental
preferences
1973 - hens and flooring options
– offered various pairwise choices
– slightly preferred traditional chicken wire
Problem of familiarity
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Dawkins (1977, 1980, 1981) reported that
hens that had lived in battery cages, on the
first day given a choice between the cage
and a grassy, outdoor run chose the battery
cage; (thereafter the trend was strongly
reversed)
Other preference studies...
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Pigs prefer substrate to root in.
Hens prefer access to a dust bath.
Mink like a swimming bath.
Recent work - ISAE, 2000 (Tucker et al.)
– Dairy cattle preference tested on bedding
choices chose sawdust more than sand or “cow
mattresses”
Using preference testing to evaluate
horses’ housing preference
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Our weanling horse study showed
preference for being by penmates vs. being
by self
showed they would work hard to engage in
grazing
I would have liked to preference test
whether they preferred the paddock or the
stall and how hard they would work for
preference
Asking suitably complex
questions...
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Some initial pig work on whether or not
they prefer pens w/ straw bedding gave
inconsistent results
– prefer or avoid depending on environmental
temperature
– strong increase in preference for straw, preparturition (Steiger et al., 1979, Fraser, 1985)
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Ongoing research on horses looking at the
“need” to exercise
– horse given a Y maze choice as to whether to
go back to its stall or go onto a treadmill and
trot
– they concluded that horses do not “need” to
exercise…do we agree with conclusion?
Assessing the strength of
animals’ preferences
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Just because a preference is shown does not
necessarily mean an animal’s welfare is
unfairly diminished when it does not have
access to that choice
– e.g. horses prefer corn to oats and alfalfa to
brome grass - does that mean the horse has poor
welfare if fed oats and brome grass? (not if the
oats and brome meet its nutritional needs)
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Dawkins (1983) studied hens’ motivation to
dust bathe
compared dust bathing to desire for food
after 0, 3 or 12 hours of food deprivation
at 0 hours, they had stronger motivation to
dust bathe
at 3 hours, the motivation was about =
at 12 hrs, food motivation was greater
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This type of testing has given rise to using
economic principles to evaluate motivation
toward preferences
– Commodities for which a given percentage
increase in price results in a decrease in the
quantity demanded are said to have elastic
demand and are sometimes called luxuries;
– those for which a given percentage increase in
price results in little change in the quantity
demanded are said to have inelastic demand
and may be called necessities
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Matthews and Ladewig (1994) used these
concepts to evaluate pigs’ needs for food or
social contact
pigs had to perform an operant response
(pressing a nose plate) to receive food or
social contact
as they had to press an increasing number of
times, they would still do this for food, but
did it less for social contact
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Can use similar philosophy to evaluate what
an animal will work to avoid (aversion
testing)
Rushen (1986) tested sheep that were
sheared with electroimmobilization and
sheep sheared without electroimmobilization
and determined sheep learned to avoid the former
option
Conclusion
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How do preferences impact welfare…
– if preferences have the backing of strong
motivation, one must assume that the animal
“suffers” to some degree when it cannot
perform that behavior (e.g. horses and grazing)
– but if biological functioning is not impacted
and, perhaps, animal develops compensatory
behavior (e.g. sham grazing) - is the animal’s
welfare impacted?
– I believe, yes, but this is not a universally held
belief