Hind leg degeneration (HLD

This is typically seen as rats gradually loosing strength in the back legs, first expressing itself with a mild shuffling or stumbling gait and a tendency to walk flat footed.  This then gradually develops until the rat has little to no use of its back legs.  You will also gradually see a loss of muscle tone around the hindquarters and back, making a their flanks look quite pinched and often feeling bony to the touch, especially along the spine.  Often their tail will become very floppy too starting from the tip and progressing backwards.  HLD generally occurs earlier in males than females, this could be linked to their increased size and likelihood of being overweight (and so more stressors on the body), their tendency to be lazier than girls or possibly the fact they are more prone to kidney problems than girls.

There are 3 main types of HLD; 

• The first is sometimes known as hind leg paralysis or nerve degeneration, it is thought to be caused by the nerves within the spine beginning to fail and wear out, this causes them to function less and less effectively at sending messages to the legs and tail, meaning they slowly but surely stop working.  This is exacerbated by the gradual weakening meaning the rat doesn't use the muscle as much and so it loses more tone and triggers the nerves less, which means they work a little less effectively and so on.  It is an inevitable part of old age if a rat lives to this point, however there is a lot you can do to slow the failure down and make it occur later in life.  As well as feeding (which is discussed later) keeping them fit and active for as long as possible makes a real difference.
• The second (which is rarer) is caused by arthritis and does mimic hind leg paralysis to some extent, not least because they often occur alongside each other.  In this case it is caused by the wearing out of the rats joint, particularly the soft part of the joint which cushions movement and shock, this is then made worse by swelling around the damaged area which can be quite painful.  Identifying it as opposed to HLD is useful as whilst it is good practice to feed in case they have it, rats can benefit from anti-inflammatory medication which can impact on other conditions so is only worth trying if you believe this might be present.  In identifying it look for symptoms of pain whilst moving, a lack of mobility in certain joints or pain when the joint is gently manipulated.  The rats may also look very stiff when they walk, rather than the floppiness associated with paralysis.  If this is the case trying an anti-inflammatory to see if it improves mobility should indicate if it is or not.  If it does improve then the minimum dose required to keep the rat pain free alongside a good diet should make a big difference.  It’s worth noting that an anti-inflammatory will make kidney failure worse, so care should be taken to only use it if the rat benefits from it.
• The third type of HLD is thought to be caused by kidney failure, however there is no confirmation that this link exists.  It is more likely that as both are very common in old age and so coincidentally occur together in most cases.  The main potential link I have been able to find is the tendency for kidney failure and degeneration to lead to a calcium deficiency (due to a decreased ability to absorb it), this can cause calcium to be leached from the bones which in some cases can accumulate as crystals in the joints mimicking arthritis.  There is also the link that with kidney failure rats are less able to digest protein, this means they cant effectively build muscle as well.  The first places to loose muscle tone when a protein deficiency hits is the tail and hind quarters, hence HLD.

Specific dietary assistance – HLD

In addition to the protection diet listed above;

• Ensure they get good quality oils daily, this can help maintain healthy joints, if you are using linseed/omega oil to support kidney failure this will cover both issues.
• Ensure your rat is kept to a reasonably healthy weight, diet them if they are massively overweight, though take it slowly as they can begin to lose weight rapidly due to other conditions such as kidney failure.
• Glucosamine can help significantly if they are suffering from arthritis based HLD, feeding 1/10 of a human dose, or 1/3 of a dogs dose seems to work well.
• Senilife or supplements high in B-vitamins.  These support the nervous system and may help repair or slow down the damage to nerves that can be linked with hind leg paralysis.