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What animals can tell us about about their needs and preferences

There are several ways of assessing animals' preferences. These include:
  • observing how an animal prioritises its activities and divides its time between different behaviours, and how this can be influenced by changes in its environment.
  • measuring how much effort or time an animal is prepared to spend in order to obtain a particular "reward" or to avoid an unpleasant situation.
  • testing how an animal's deprivation of different environmental features increases physiological measures of stress.

Interpreting the results can be difficult. It is not immediately obvious, for example, whether an animal that is behaving abnormally but has low physiological indicators of stress is better or worse off than one that is physiologically stressed but behaving normally. In each case, there may be additional subjective experiences such as frustration and anxiety that are important in human experiences but much harder to measure and assess in other animals. The relationship between motivation, stress and welfare can be complex. For example, an animal may not be motivated to visit a vet, but despite any associated stress, its welfare may be improved by doing so.

Scientists at the University of Oxford have made important advances in addressing some of these issues, not least in bringing together motivational and physiological measures to assess systematically how animals value different resources.

The Oxford researchers explored how the rearing environment, the provision of objects that stimulate a response and the opportunity to perform different behaviours influence how mink choose to spend their time.

The study was funded in part by the Universities Federation for Animal Welfare. It involved round-the-clock observation of mink which had been reared from birth under farm conditions, and which came from a line bred in captivity for over seventy generations.

The animals were given the opportunity to 'pay' to reach a variety of resources, by pushing doors weighted with increasingly heavy weights. They could choose to visit one of a selection of environmental features : "toys", free space, swimming bath, raised platform and an alternative nest site. Responses to increasing costs were analysed using techniques from human economics.

The mink proved willing to pay in order to do many natural behaviours, such as investigating tunnels and exploring novelty, but rated swimming as their most preferred activity. When access to swimming-water was withdrawn, animals had levels of the stress hormone, cortisol, in their urine comparable to those associated with food deprivation.

Several new avenues of research are being explored as a result of this study. First, although these results showed that the animals were stressed when they were deprived of access to a bath in which to swim, they do not necessarily mean that farmed mink suffer in the same way. The mink in the study were allowed to swim in a bath and later denied access to it, whereas farmed mink never have such access, and for them it may be a case of "you don't miss what you've never had". Second, it is still unclear whether it is access to water or swimming itself that matters most to mink. This distinction will be important to regulators, animal welfarists and farmers in considering ways of reducing any stress that there might be on farms. For example, the introduction of spray/sprinkler systems alone could be beneficial.

This research offers some of the best methods so far developed for determining animals' priorities. It has potential for understanding animal preferences, and for aiding the design of accommodation and conditions to meet them, for a range of species and situations including, for example, laboratory animals and animals in zoos. At Silsoe Research Institute, scientists, vets and engineers have been identifying the environmental preferences of pigs, hens, ducks and turkeys. This research has led to guidelines on various environmental features such as air quality, and in some cases has overturned previous recommendations which were shown not to be in accord with the animals' preferences.

Environmental stresses are rarely experienced individually. Researchers need to be able to recreate the various combinations of stresses that animals might encounter and then study how they respond to the different combinations. At Silsoe Research Institute a choice-chamber is used to see how poultry respond to combinations of heat and vibration typically encountered in transporter vehicles. The birds could choose between compartments with heat, vibration, heat plus vibration and a control with neither heat nor vibration. Broiler chickens avoided vibration, but not heat, at least initially; and combined heat and vibration did not affect them significantly more than vibration alone. Birds avoided entering the heat compartment for longer than ten minutes, suggesting that while they might find heat initially pleasant, it can become aversive as the birds begin to overheat. Under conditions where the birds could not move away from the heat this would obviously increase stress.

In a separate system for studying the way birds rate the unpleasantness of different situations, chicken have been trained to run along a corridor into a goal-box in which they receive either a food reward or experience a potentially stressful condition such as confinement or heat and vibration. The longer a bird takes return to the goal-box to seek the food reward, the greater aversion it had to the previous treatment. Confinement, for example, appears not to be particularly stressful: after being confined, birds rapidly return to the goal-box. This methodology provides a way of quantifying animals' response to different combinations of potentially stressful factors. The objective of the research is to understand how animals interact with their environment and to facilitate the design of conditions that minimise stress.

For some animals, performing a particular behaviour may be an important goal in its own right. Researchers at Roslin Institute investigated the relative value hens give to resources such as food, nest building materials, a dustbath and a social partner with whom they can interact. Nest building turns out to be very important to hens. They will willingly overcome different obstacles such as water baths or fans or doors and will walk considerable distances to reach a nest site. They will spend as long on a full repertoire of nest building behaviour when provided with a pre-formed nest they have made earlier, as they will on making a new nest (see also page 34). When given different materials, hens prefer nests that they can mould by body and foot movements rather than by their beaks. This suggests that having loose nesting materials such as wood shavings (which are moulded by both sets of activity) is less important to the hen than having a nest that allows moulding movements.

The extent to which animals will work to avoid unpleasant situations also provides clues about their priorities. For example, when fast growing broiler hens that have become lame will perform work in order to gain access to pain killers, this is strong evidence that the lame birds are in pain.

A similar approach in which scientists can identify what animals will endure in order to win a reward, e.g. a food treat, may be helpful in ascertaining how laboratory animals respond to, and rate, different experimental procedures such as having blood samples taken.

Studies at Roslin Institute showed that hens can learn to avoid an unpleasant experience. In this research, a light in the cage flashed shortly before the rapid inflation of a balloon. Hens learnt to move into an adjacent compartment when the light flashed in order to avoid the inflating balloon. Giving animals the opportunity to recognise and move away from potentially frightening experiences is an important element in improving welfare.

Source: The Biotechnology and Biological Sciences Research Council - Summer 2002

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