Rat Café - From fatness to fitness
Alison Campbell

Patterns of obesity in rats closely follow patterns of obesity in humans, and rats have been widely studied to try to unlock the causes and issues surrounding this condition. Often when we think of obese rats we think of the Zucker strains, bred specifically to research the genetic propensity to obesity, but there are actually many strains of rattus norvegicus that produce obesity prone individuals. This has been shown to be a genetic predisposition and is testable (by feeding a high fat diet) at a few weeks of age (the predisposed rats will put on weight faster than the others in the litter).

From what I have heard and observed these traits are widely spread throughout the pet rat population; how many of us have watched one rat out of a group of fit lean rats grown increasingly spherical? It’s a problem I hear of repeatedly from rat owners across the UK.

Obesity prone rats generally have decreased energy expenditure and a lower sleeping metabolic rate. They may not utilise stored fat easily, and have a decreased sensitivity to insulin (needed for glucose metabolism).

Prevention
Obesity is always better prevented than treated. Weight loss in affected animals is generally difficult to achieve, primarily because any energy (food) restriction leads to a further increase in metabolic efficiency (reduced energy expenditure and reduced sleeping metabolic rate). It is also very difficult to place an individual rat on a diet, without the rest of the colony being affected.

Physical exercise is the key factor that counteracts the metabolic efficiency in these animals, and is an essential part of any weight management programme. All rats should be given maximum exercise opportunities and it is a good idea to arrange their environment with this is mind (removing ramps and ladders, placing food and water well away from sleeping areas and arranging furniture so that the rats have to climb to reach the desired spot). Sadly, modern cage designs often promotes lack of activity by allowing our rats to amble from level to level up shallow ramps, and then flop onto a hammock! They rely on us to provide an environment where they have to work to get where they want to be. Alongside this time out of the cage, exploring, stair climbing etc will help to keep your rats fit and at a good weight.

There has been a tendency amongst rat owners to overfeed their rats. I suspect that this is partly due to the fact that rats seem to derive a great deal of pleasure from eating, so caring owners are always looking for new treats for their pets. It may also be due in part to simply overdoing good diet. Even ad lib availability of dry mix is actually overfeeding for rats, and many owners also add in a fair quantity of fresh food. Adult rats should be fed daily in the evening, and should have a few lean hours prior to being fed. Research clearly shows that if rats eat 10-30% less than they would if food is given ad lib, then they will tend towards healthier and longer lives. In simple terms, rats will tend to overeat when food is freely available. Adult diet should also be carefully chosen to be very low in fat (4% is adequate).

Reducing the variety available in a grain mix tends to reduce intake. Therefore dry diet should be limited to one or two base foods and perhaps a little sugar free cereal. As human cereals are already processed they are often more readily digestible and easier for rats to gain nutrients from than straight grains. So be wary of feeding too many.

Treatment - diet for weight reduction
Options for main diet:

• Pellet free rabbit food with the addition of sugar free cereal (Shredded Wheat, rice cakes) as around 50% of the diet, and Nature diet lite dog food as the other half (approximately one eight of a tray per rat per day).
• A couple of pellet free rabbit foods mixed (with or without the addition of sugar free cereal).
• For short periods a low fat rat nugget/complete food may be useful for some rats.

• green leafy vegetables (kale, spring greens, herbs)
• carrots
• broccoli
• cucumber
• tomato
• watermelon
• berries (strawberries, raspberries, blue berries)
• apple

Weight reduction general points
Boost metabolism by:

• Increasing exercise opportunities.
• Keeping the room temperature cool.
• Supplement with GTF (glucose tolerance factor) Chromium and Green Tea Extract (available from Holland and Barrett).

If your obese rat is one of a mixed colony, feed the whole colony on a reducing diet (as above) but give the slimmer rats some higher calorie fresh foods/treats whilst giving the weighty ones some extra out time.

Stimulate activity whilst out of the cage by giving them toys to play with and new items to explore.