After the Brambell Report, scientists paid much more attention to animals' confinement and its impact on animal welfare.
3 Strategies for Examining Effects of Confinement on Animal Welfare
The Philosophical Approach looked into the extent that animals could have cognitive awareness and were sentient to feel and perceive the world around them.
The Scientific Approach - which used the animal's behaviour to see the effects of stress on the animal's body and mind.
The Engineering Approach looked at how animal husbandry systems were designed and if they could be made better by making simple changes.
Once it had been agreed that animal welfare was, in fact, important, scientists began to ask the following questions:
Were there objective measures of animal suffering?
In what way were animals suffering when they were confined?
What level of suffering would be considered acceptable if suffering couldn't be totally avoided?
What changes could be made to lessen suffering?
Professor Andrew Fraser and Professor Donald Broom wrote a book entitled Animal Behaviour and Welfare (1990), and in this book, they discussed whether it was cruel to keep an animal in a cage. They concluded (as below) that the best way to understand welfare is to understand how the animal perceives its own world.
"The effects on the individual must be considered when assessing welfare. It is that, for some species of animals, the welfare of most individuals in captivity will be poor, however many people try to improve them. For other species, however, the welfare of most individuals may be good. For every species, a detailed study of the behaviour and physiology of individuals can reveal whether their welfare is poor. We have got to get as close as we can to the rabbit's world as the rabbit sees it and responds to it. Various forms of deprivation, discomfort, and pain are important to the rabbit and lead to indicators that tell us that the welfare of the rabbit is poor. There is much evidence showing that animals have sophisticated systems for regulating their lives and that they are much disturbed if they cannot control certain aspects of what happens to them.
Confinement Impacts Animals Physically & Mentally
If an animal is confined and its movement is restricted, it may not be able to carry out its full behavioural repertoire, and this is not allowing it the freedom to express itself. Confinement does impact the animal's behaviour in the following ways:
Stereotypies - a repetitive or ritualistic movement, posture, or utterance. Stereotypies include tongue playing, bar-biting, pacing, circling, neck-twisting, head bobbing, weaving, swaying, rocking, self-mutilation, vomiting and regurgitating, playing with and eating excrement. You can read up on each of these stereotypies here. For a good paper on stereotypic behaviours in pigs, click here.
Rebound behaviours are behaviours that happen when animals are kept in confinement for a long time and then released. Once the animals are released and have more space to perform the behaviours, they increase sharply. In the case of hens who were kept in small cages and released after 9 months in a study by Nicol, preening and stretching increased.
Animals who are confined are also at physical risk. A good example of this is shown in the increased incidence of Osteoporosis in laying hens kept in cages long term. Their bones are weakened because they did not have enough space to move around to keep their bones healthy. This review on laying hens and osteoporosis can be found here.
How is welfare measured?
Physiological & chemical changes
Self-administration of tranquilisers
This is a simple way; it basically means that if animals are dying in a confined space, there is something wrong with that environment.
This will gauge the strength of motivation for a reward, and it is the basis for practical research.
Farmers will say that if an animal is producing eggs, milk etc. and is growing, surely the animal's needs must be met. This is not always the case because other factors affect the animal's overall well-being, such as disease or unacceptable stress.
This testing method gives animals a choice to select which option or environment they like best to determine which they see as the most pleasing situation. This is a simple method, which involves just asking the animal. The study already mentioned by Christine Nicol looked at whether hens preferred larger cages tested over a period of 9 months. There was a school of thought that hens would become used to their space after a while. This was not the case!
Physiological or Biochemical changes
Corticoid hormones and lymphocyte/heterophil ratio are used as an index of stress.
Self-administration of tranquilising drugs
This is a way to assess anxiety.
You can read more about measuring animal feelings here.
The behavioural need can be demonstrated by the need of animal to carry out a certain behaviour.
Nesting behaviour in laying hens is a behavioural need, as demonstrated by Hughes et al., which showed that hens are given a preprepared nest still wanted to make their own nest and did not stop nest-building behaviour. You can check out this study here.
In a similar study in pigs, nesting behaviour was also strongly motivated. You can find this study by Arey here.