In domestic homes with more than one cat, the cats may coexist but they may not actually be part of the same social group, and are forced to share the space and resources such as food and water bowls and litter trays. This can cause competition for resources, which can lead to high levels of stress in a cat if the other cats are seen as a threat. This competition introduces a sense of unpredictability and lack of control. More assertive individuals may even monopolise resources, further limiting access by the other cat( s).
In some situations, cats will learn to share resources, and will use subtle communication cues to avoid conflict or will even avoid each other entirely. However, often cats do not have enough space to completely avoid each other, and may not adapt to living with another cat. This can lead to each of the cats living in a constant state of stress, which can have negative physical and psychological effects.
Stress has been proven to weaken the immune system; cats that live with chronic stress are five times as likely to develop upper respiratory disease compared with cats in a low-stress environment, as latent feline herpesvirus can become reactivated and cause clinical signs [ 7 ]. Another common disease associated with stress is feline interstitial cystitis. The repeat activation of the sympathetic nervous system due to stress alters the permeability of the bladder wall, causing haematuria and dysuria [ 7 ]. Behavioural consequences of stress include anorexia, inhibition of normal behaviours and inappropriate urination in the household [ 7 ]. Owners may not recognise the subtle signs of stress and think that their cats get on well together when they see them sharing resources. Only when cats show more overt signs, like the ones mentioned above, might owners recognise there is a problem.
Factors affecting cat relationships
There are a few factors that can influence whether cats get on with each other and can be part of the same social group. However, these are not set in stone, and there may be many other factors that influence whether individual cats will develop a positive social relationship.
Studies have found that cats that are related to each other are more likely to spend time in close proximity to one another, and to allogroom, compared with cats that are unrelated but familiar [ 8 ].
Genetics play a large part in the personality traits of cats and can affect whether a cat is likely to be sociable around other cats or find a multi-cat household stressful. A large study conducted by Salonen et al. [ 9 ] looked at 5,726 cats, and found significant breed differences when it comes to social behaviour. For example, breeds such as the Turkish van and Bengal are most likely to show aggression towards other cats, whereas Maine coon, Devon rex and Persian cats are least likely to show aggression towards other cats [ 9 ]. Breeders should breed based on the temperament of the mother and father; a bolder and more confident father is more likely to have bold and confident offspring [ 4 ]. This will have benefits not only within multi-cat households but also in other aspects of the cat ' s life.
Socialisation also plays a major role in whether a cat is likely to find a multi-cat household stressful. There is a sensitive period early in kittens ' lives, between 3 and 8 weeks of age, when socialisation is key. During this time, kittens are more sensitive to stimuli in their environment and will learn more skills [ 4 ], so it is imperative that they are exposed to a variety of people, cats and environmental stimuli [ 4 ]. Positive socialisation means kittens are less likely to develop negative associations and fears around environmental stimuli and will be better able to cope in different situations as an adult.
During the sensitive period, kittens also begin to learn social skills through play with their littermates. This play helps them learn which social behaviours are acceptable, and encourages them to associate other cats with positive experiences [ 4 ]. Social play peaks between 9 and 16 weeks of age and, although this is outside the sensitive period, it underlines the importance of socialisation throughout a cat ' s early life. It also highlights the vital role of breeders in the socialisation of their kittens, as this period occurs before kittens go to their new homes.
Reducing stress within the household
The Five Pillars of a Healthy Feline Environment is a framework developed jointly by the American Association of Feline Practitioners and the International Society of Feline Medicine [ 3 ]. The framework outlines the key aspects of a cat ' s environment that are needed for it to live a healthy and stress-free life. The five pillars are as follows [ 3 ]:
• Pillar 1 Provide a safe space
• Pillar 2 Provide multiple and separated key environmental resources
• Pillar 3 Provide opportunity for play and predatory behaviour
• Pillar 4 Provide positive, consistent and predictable human – cat interaction
• Pillar 5 Provide an environment that respects the cat ' s sense of smell.
It is imperative that there are enough resources to support all the cats in the household without any competition between individuals. Ideally, there should be one resource per cat, plus one, so each cat has a choice of resources. For example, in a household of three cats, there should be at least four litter trays in different locations around the house [ 6 ]. Table 1( page 29) highlights ways in which resources can be distributed to reduce stress.
28 Veterinary Nursing Journal