Pet Q & A: My 12-year-old cat has lost a lot of fur on his back and hind legs.

Q My 12-year-old cat has lost a lot of fur on his back and hind legs. I have treated him for fleas several times but it makes no difference. What else can I try?

A Fleas are the most common cause of fur loss in cats and it is important to check that you've used an effective flea treatment. Those available over-the-counter do not tend to be as effective as those obtained from your vet, so if you have used a product from a pet shop or supermarket it may not have destroyed all of the fleas that could be present.

When you treat any pet for fleas it is also important to treat your home too using a suitable product (usually a spray). This is because flea eggs and larvae live in your house (eg in carpets, rugs, your pet's blankets), in addition to the fleas which feed off your cat. If you only treat your cat you are not eliminating the fleas completely so the eggs laid elsewhere within your home will hatch and infect your cat.

However, your cat's problem could also be caused by another condition such as a skin infection so I would strongly recommend taking him to your vet.

Q I give my guinea pig healthy food and occasionally biscuits as a treat but recently he seems to have lost his appetite. Any advice?

AIf any pet goes off their food this can be a sign of a medical problem so you should take your guinea pig to be checked by your vet. It is not a specific sign, as there are lots of conditions that can make an animal feel unwell and lose its appetite, so your vet will do a thorough examination.

Stress can also be a cause. Guinea pigs are nervous animals and need places to hide (eg cardboard boxes and tubes), and can be easily alarmed by children or other pets (eg dogs and cats). All pets need five things to be healthy and happy, called the five "welfare needs". To find out how to meet the welfare needs for guinea pigs, including information on what they should be fed, visit www.pdsa.org.uk/guineapigs.

Q My German Shepherd is constantly chasing her tail. It was funny to begin with but now we think it might be more serious. Should we be worried?

A There could be a medical reason for this, such as pain in her tail or blocked anal glands, so you should visit your vet to rule these out. Another possibility is that your dog is displaying compulsive behaviour. German Shepherds are prone to compulsive tail-chasing, so this is certainly possible.

Treatment involves identifying situations that trigger the behaviour and removing these if possible. Introducing a set routine and obedience training using reward-based methods is also needed. Medication may be recommended to help with the treatment. Never punish a dog that has compulsive behaviour as this adds to the dog's anxiety and will make the problem worse.