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Photo by Anne Searight

The Fat Sand Rat (Psammomys obesus) lives in the sandy deserts of Libya, Egypt, Palestine and Arabia. I know it looks just like a North American gopher. Having seen a Fat Sand Rat I must admit I at first thought it was a gopher. The Fat Sand Rat is a large rodent. Significantly larger than a rat.

Fat Sand Rats in Captivity

by Eddie Cope

This article first appeared in the September 2001 issue of the NGS Journal.

Introduction

The Fat Sand Rat gets its common name from when diabetes was first discovered by chance observation in the specimens collected by the US Naval Medical Research Unit in Egypt. It appeared when animals were maintained on a regular rodent diet. These first animals were trapped on the sandy beaches of the Nile Delta and trivially nicknamed 'Sand Rats', this is a misnomer as they are a highly specialised members of the gerbil family. Both the common and Latin name (Psammomys obesus) suggest that it is bulky in stature and this is certainly true of the adult males, females however remain leaner, considerably faster and more agile.

Distribution and Behaviour

Fat Sand Rats can be found in Libya, Egypt, Coastal Sudan, Israel and Saudi Arabia in sandy saline deserts with sparse vegetation. Sand Rats are diurnal, being active both in the day and night. They have complex burrow systems which have separate chambers for nesting, breeding and storage of food. Due to its environment it has evolved into a highly specialised rodent. Its staple diet is the Salt Bush Plant (Atriplex Halimus) supplemented by some leguminous plants, annuals and occasional insects. It copes with the high salt intake in its diet by having extremely efficient kidneys that produce urine with a high salt intake without being toxic to the animal. In the wild they rarely drink water, having their needs met by their diet and the licking of morning dew. They appear in the early morning hours at the mouth of the burrow cleaning out dirt and excreta, only after these home cleaning activities are done does it begin its foraging. Food is first eaten directly from the adjacent bushes (burrows are found mainly near or within clumps of Salt Bush). Later, after their initial appetite is sated they begin to gnaw off branches and take them to their burrow. Fat Sand Rats live solitary lives in individual burrows except for mothers with offspring during the breeding season which is January to April. Mating takes place by chance encounter. They are active on the surface during the day in the winter months, but during the summer months they prefer the shade and can be found inside the burrow or in the shade of the surrounding bushes. In captivity these animals are very intelligent and docile creatures.

Sand Rats in Science

The induction of diabetes in Sand Rats suggests the value of this rodent as a laboratory research animal, however their supply to the research community is severely limited due to breeding difficulty and maintenance. To date there are only two active research colonies in the World, the main research is on obesity and diabetes, the most successful being the research on the newly discovered 'Beacon' gene, localised in the hypothalamus (the part of the brain which controls food intake). This discovery has proved that obesity is largely genetic. Research has shown that it is possible for the rodent to have a litter of 3 - 4 individuals all with different genetic composition, one pup would overeat and develop obesity, another pup would overeat and develop obesity and diabetes, other would just develop diabetes or neither. So by environmental manipulation it provides excellent study of the genes involved because the differences in the animals have to be genetic differences. The first man to succeed in establishing a durable and reproducible colony was a Dr. Jonathon Adler who in the early 70's set up the now famous colony in the animal farm of the Hebrew University Hadassah Medical School. The animals there were originally collected from the desert area north of the Dead Sea in Israel. They were maintained on a 'free choice' diet consisting of their native desert staple, the succulent leaves and branches of the salt Bush (Atriplex Halimus) plus a few pellets of regular rodent chow. These animals are known as the H.U.P.O. strain in research (Hebrew University strain Psammomys Obesus).

Feeding and Maintenance in Captivity

At present I am maintaining two pairs on different diets, the first pair consists of using 50g daily per rodent of baby leaf spinach with occasional broccoli or cauliflower thrown in to make up the 50g. Also a 3% salt solution is used in the drinking water. A weekly vitamin supplement and a once a week (small) supply of mealworms is also recommended (however, one pair refuse to eat them). In addition to the vegetables 5g of low energy high fibre pellets are given daily to each rodent. This diet is based on the research of Jack Fine and Fred Quimby from the College of Veterinary Medicine, Cornell University and Dorothy Greenhouse from the Institute of Lab Animal Resources. The second diet consists of 7g of Alfalfa pellets daily each with a single lab rat pellet given individually to each animal. Also weekly vitamin supplements and a small ration of live food, plus a 3% salt solution in the water supply. Up to now I have had few problems with these diets, although the former diet involves a lot more tank changes due to the production of extra urine.

I also use a glucose check stick (which can be bought over the counter at pharmacists) once a week to test for diabetes. By gently pressing the lower abdomen a small amount of urine is produced and this can then be tested for diabetes. Up to now all tests have been negative.

Why salty water? Well initially specimens were kept on alfalfa with plain water and there was a high mortality rate in the rodents, post-mortem results showed that the animals suffered from adrenal pathology and other signs of chronic stress. Since alfalfa contains little salt 9% ash weight versus 37% in salt bush it was speculated that they were suffering from salt deficiency and from then on a 3% raw salt solution was added to the water. This salt is from evaporated sea salt (no additives) and presumably this contains other minerals. As a result there was no recurrence of the pathology. Also as a point of note Alfalfa contains an active oestrogen (cumestrol) which might affect breeding adversely. Tests however, have shown it has no effect on breeding activities.

I keep my pairs in 3ft glass aquaria, they have thick cardboard tunnels with wood shavings, shredded paper and toilet roll for bedding. With my original pair, at first I added several nest boxes as well as the tunnels, trying to simulate the multi chamber burrows they have in the wild, however the male not being as agile as the female kept injuring himself when he tried jumping from the top of the nest boxes, so these were removed. They now make their nests behind the tunnels. No hay is added to the bedding as this would be eaten and the controlled diets I have them on would be adversely affected.

Breeding is the one area where I have been unsuccessful with my Sand Rats. It has already been said that the breeding season is January to April, however breeding successes in both captivity and the wild are poor, and much research has gone into this.

A high rate of sterility has been found in captured male specimens and despite optimum diets and a light regime of 10/12 hours dark and 12/14 hours light breeding in captivity is still low. Gestation is 24 days, if a successful mating takes place, the mother will produce 3 or 4 pups with 75% reaching weaning age. My first pair have showed no signs of mating in the time I have had them. The second pair have mated many times, but unfortunately a litter has not yet been produced. I have noticed blood in the tank however a few days after mating on several occasions and I am therefore assuming that the female is miscarrying within the first week of pregnancy, however I live in hope!

Both my pairs, although not as social as the Shaws, do enjoy some handling and time out of the tank, they know when its feed time and when I go in the tank they do not run and hide, but come and greet me and often sit in my hand eating their spinach which they roll up from either side to form a sort of 'Hotdog'.

I sincerely hope Psammomys Obesus becomes firmly established in this country, on a hopeful note I have recently heard of one breeding success in the UK with this animal, with intelligent breeding plans hopefully it will become a regular feature in many Gerbil enthusiasts collections.

Acknowledgements: Special thanks to Dr. V. Michelle. Chenault, Uniformed Services University of the Health Sciences, Bethesda, Maryland.

References:

Establishment of Conditions for Colony Breeding of The Sand Rat. G. Frenkel, Y. Shaham and P.F. Kraiger.

Diabetic Response of weaning Sand Rats. J.H. Adler, G. Lazarovici, M. Marton and E. Levy.

Achieving predictable model of Type 2 diabetes in Sand Rats. J.H. Adler, R. Kalman, G. Lazarocici, H. Bar-on and E. Ziv.

Breeding Sand Rats with a diabetic predisposition for Laboratory Investigations. J.H. Adler, Ch. Roderig and A. Gutman.

Walkers Mammals of the World, Nowak and Paradiso.

There are some more pictures of this unusual species at Gerbil-Info.

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