The specific nutritional requirements of ageing cats and dogs have not been widely studied, and it is only recently that investigations into the processes of ageing in cats and dogs have begun. The increased life expectancy of companion animals, resulting mainly from more sophisticated veterinary care, improved nutrition and heightened owner-awareness, has stimulated interest in the changes associated with ageing and the possible role that nutrition may play in delaying such changes. It has been estimated that approximately 35% of dogs and 30% of cats are aged over 7 years (Venn, 1992) The age at which a cat or dog can be considered old is one of great debate and is particularly complicated in the dog because of the variety of breeds. In general, ageing occurs more rapidly in the larger breeds, with small breeds exhibiting the longest life-span Thus, giant breeds such as Great Danes are reported to have a life expectancy of about 7-8 years, while toy breeds such as Yorkshire Terriers and Dachshundshave a life expectancy of about 12 years (Legrand-Defretin & Munday, 1993). The maximum life-span achieved by a dog is reportedly 27 years, although it is rare for them to live more than 20 years (Macdougall & Barker, 1984), Cats, on the other hand, donot display a breed-effect with respect to ageing (Griffith, 1968). They have an average life expectancy of 14 years yet the oldest recorded cat is known to have lived for 36 years (Mosier, í978). The individual variability clearly makes it difficult tohave a precise definition of geriatric It has been suggested that a geriatric cat or dog is one which is in the last third of its anticipated life-span, although perhaps it is more realistic to categorize an animal according to the point at which visible signs of ageing become apparent. The obvious signs of ageing, which are common to both cats and dogs, are whitening of the hair and a general decline in coat condition, failing senses i.e. sight and hearing, and lethargy. In addition, there are often marked behavioural changes including irritability and nervousness (Mosier, 1978).
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