Geriatric rats – what could go wrong?

Rats can make remarkable pets and are certainly not the pests that people often think. They are calm, intelligent and social creatures, and when handled regularly, are unlikely to bite. For this reason, they make excellent first pets for younger children. With improved husbandry, nutrition and preventive health care, they are now frequently living into old age. With this in mind, we need to be aware of the disease's rats are susceptible to as they age.

Posted: 19 March 2020

Geriatric rats – what could go wrong?

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In the wild, rats are prey animals and tend not to show signs of pain or disease. This makes it difficult for some owners to spot illness early, and as a result are frequently brought to us in for the first time in advanced stages of disease.

In this article we look at three of the most common senior presentations.

Three common geriatric diseases

1. Chronic progressive nephrosis (CPN)

This is probably the most common disease of older rats. The condition may be seen in animals as young as 3 months of age, but it typically found in animals over a 1 year. The incidence and severity of the disease occurs more frequently in the geriatric male rat (as many as 3 out of 4 older males are affected!).

The disease is often subclinical, with signs only being noticed when more than 75% of renal function has been lost. Early signs to look for include;

  • Gradual weight loss – even in the presence of an unchanged appetite.
  • Lethargy – this may be seen when the condition is quite advanced.
  • Polydipsia and polyuria – as a result of nephron and glomeruli damage.
  • Loss of appetite – the multiple physiological changes associated with renal disease, including uraemia, will eventually suppress the appetite.
  • Proteinuria and albuminuria – this is frequently reported.
  • Uraemia and raised creatinine – blood tests are worth running to help diagnose and monitor the patient.
  • Enlarged kidneys – they become swollen in the early stages and are easy to palpate. As the condition progresses the kidneys will shrink and become fibrosed.
  • Hind limb weakness – this may be seen when the kidneys become unable to control blood phosphorus and calcium levels.

What are the causes of CPN?

There are a number of predisposing factors, such as;

  • Age – the condition is almost always found in older rats.
  • Sex – male rats are considerably more at risk.
  • Protein – refined high protein diets should be avoided.
  • Overfeeding – offering food ad-libitum can also lead to obesity.
  • Drugs – some medications may be toxic to the kidneys resulting in renal damage. Care should always be used when using NSAID’s.
  • Endocrine diseases - diabetes results in hyperglycaemia and renal impairment.

Of all these triggers, diet is the one area we can help. The quantity and quality of food plays an important role in the development of the disease. All too often well-meaning owners are keen to feed their pets with an ad lib supply of high energy and high protein food. The consequences are that they suffer greater nephron and glomeruli damage, which then results in protein loss into urine. For these reasons, you can help reduce the incidence and severity of renal disease by recommending;

  • Caloric restriction – if the animal is overweight, reduce the intake by around 20-25%. By prevention of overfeeding and obesity in the first place you can delay the onset and severity of this disease even if the animal is genetically predisposed.
  • Protein restriction – a low protein, low phosphorus diet will help.
  • Omega-6 and omega-3 - polyunsaturated fatty acids and conjugated linoleic acid can be used to protect the renal architecture.
  • Fluids – subcutaneous fluids to help with dehydration may help for a short period of time.
  • ACE inhibitors - angiotensin-converting enzyme inhibitors can be used especially if the animal is hypertensive.

At Burgess Pet Care we produce some high-quality food suitable for rats, including;

2. Chromodacryorrhoea

This is a conspicuous condition, sometimes referred to as “red tears” and is the result of porphyrin staining around the eye. The normal lachrymal secretions produced by the harderian gland contains porphyrins. In animals that aren’t grooming and cleaning their faces (e.g. when they are stressed or debilitated), this can dry around the eyes and external nares, leaving a red stain or crust which can be confused with bleeding.

The production of porphyrin increases with age, so you are more likely to see this in the geriatric rat. You need to consider it as a non-specific sign of stress which can indicate an underlying medical complaint. A full clinical examination and assessment is required, where you should look for triggers such as;

  • Pain
  • Dehydration
  • Respiratory disease
  • Inappropriate nutrition
  • Poor owner handling resulting in stress
  • Environmental stressors such as aggressive cage-mates or overcrowding
  • Environment and airborne irritants (e.g. smoking by owners, perfumed candles etc)
  • Blocked tear ducts
  • Eye infections
  • Eye injury

With such cases, clean the eyes and nose daily to remove excessive or dried secretions. Ultimately the underlying cause for the over-production of the tears or nasal secretions needs to be resolved.

3. Mammary tumours

These seem to be extremely common, especially in older females, and are either fibroadenomas (the most common) or adenocarcinomas. They can develop anywhere from the axilla to the perianal area; rats have extensive mammary tissue!

Signs to look for include;

  • Abnormal mass – usually a soft, well circumscribed movable mass along the region of mammary tissue. Some can be flattened and some more firmly attached if they are malignant.
  • Ulceration and necrosis – this may be present if the skin has broken and is usually found in advanced cases.
  • Increased appetite – particularly with no weight gain. All the energy is used for tumour growth.
  • Impaired mobility – some mammary tumours grow so large that they obstruct limb movement.
  • Poor appetite and weight loss – this will be late in the development of the disease.

Calorie intake affects tumour incidence

The most important influence in the development of these tumours is diet. Rats fed an ad libitum diet generally have a higher incidence of tumours and a lower survival time.

Treatment

Surgical removal of mammary tumours is best performed early to ensure the recovery is rapid. Most rats will respond well, especially if the tumour is benign.

Prevention

  • Diet – recommend a diet that is low in fat and calories.
  • Neutering - ovariectomy reduces the development of spontaneous mammary tumours. 
  • Encourage health checks – early detection and treatment while the growth is small decreases surgical time and recovery period, as well as improving the outcome.

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