There are many types of carts available to suit dogs of all shapes and sizes. Carts are available direct from the manufacturers, or you may be able to get a second hand cart that another dog has already used. A second hand cart would be much cheaper, and very often they will be donated by the owner in memory of their much loved fur friend who has passed on. You would of course probably need to pay the shipping fee. This is quite a nice way of obtaining a cart. A cart can be obtained prior to your dog actually losing complete mobility in the hind legs. It can give some freedom back to the dog, allowing it to go on those long walks and runs it once enjoyed. If the dog is able to, it can take some walks without the cart as well. Most dogs seem to adapt to their carts within the first 1 or 2 goes, there is no stopping them once they get going! If your dog has already lost complete mobility, a cart can be a wonderful thing. It can put the sparkle and zest for life back into your dog.
When to put your dog into a cart is a difficult decision to make. You need to keep your dog walking for as long as possible. Once he stops walking he will lose his muscle mass and become weaker, quicker. However, if he is getting too weak to go on a walk he will then be using less muscles in the front. These muscles can then start to lose strength. So, by putting him into a cart it will allow him to keep exercising the front . He needs the muscles to be strong to help with the loss of muscle mass at the rear. If you are using a cart prior to your dog losing complete mobility in the hind legs try to also keep him walking without it, even if just for very short distances.
Here are links to some of the popular brands of carts: