Dwarf Ratten - the dwarfs under the rat

Kathrin Guttmann Body, Knowledge, Breeding & Genetic

Dwarf rats 40-75% smaller than standard rats, but they don´t show any health restrictions., They even have a higher life expectancy.

The history of the dwarf rat (dwarf rat)

In his book "Genetics often he Norway Rat" Robinson1)Robinson, R. (1965) Genetics oft he Norway Rat. Pergamon Press, Oxford already describes two dwarf mutations. The first has been described 1934 by Sciuchetti and Lambert2)Rossin, A. M. and LAMBERT, W. V. (1934) A study of the inheritance and physiological behavior of dwarfism associated with an eye defect in rats. Proc. Iowa Acad. Be., 41: 317-18 described. It is a simple autosomal recessive allele. At birth, the Dwarf-1 rats were the same size as their siblings, from day 5 on 5 , the distance in the growth curves of standard siblings and dwarfs gets bigger. The animals developed fur at a later point and the fur was less dense than the standard animals. This type of Dwarf rats was more prone to illness and less vital than standard rats. All homozygous animals were infertile, the testes of males under developed and gender size differences not pronounced.

A second form of Dwarf rats has been described by Wooley and Cloe in 1939 1939 Woolley and Cole3)WOOLLEY, G. W. and COLE, L. J. (1939) A new dwarf mutation (dw2) in Rattus norvegicus. Genetics, 24: 111 described. In this type, the development slowed down after the second month of life. They had a short, rump and developed exophtalmus (abnormal protrusion of the eyes). The weight was 100 to 150 g, with males being heavier than females. The males could not reproduce, while the females had a few litters.

The Dwarf rats, that our current pet dwarf rats are derived from, have been 1977 found in a laboratory of Morishita Pharmaceutical Co. Ltd. in a strain of Sprague Dawley rats. From this new laboratory strains developed , which serve as a model for aging research or the lack of growth hormones in humans. On the other hand, some of those rats were given to hobby breeders. The first Rattery, who worked with Dwafs, war die Little Rugs Rats Rattery. The breeder gave descendants of the first dwarfs to the OFR Rattery, the RRLM Rattery and the PNS Rattery, from where the animals got to the breeder Camarattery and to Cananda. Finally the first dwarfs have been imported from Canada by Fairytale Rats to Germany (unsere Dwarfs stammen aus einer Linie aus Belgien).

Cause of dwarfism

The inhibition of the development of the Dwarf rat's size (Spontaneous Dwarf Rat, SDR) is due to the lack of growth hormone in the anterior (lying forward) pituitary gland (Hirnanhangsdrüse) ausgelöst. Because of this SDRs can serve as an animal model for dwarfism in humans triggered by a lack of growth hormones (Reading 19844)Seitaro Okuma (1984), Study of growth hormone in spontaneous dwarf rat, Nihon Naibunpi Gakkai zasshi). This lack of growth hormones is caused by a point mutation in the corresponding gene, (Takeuchi et al. 1990<95)Takeuchi, Takashi & Suzuki, Hitoshi & Sakurai, Susumu & Nogami, Haruo & Reading, Shinichi & Ishikawa, Hiroshi. (1990). Molecular Mechanism of Growth Hormone (GH) Deficiency in the Spontaneous Dwarf Rat: Detection of Abnormal Splicing of GH Messenger Ribonucleic Acid by the Polymerase Chain Reaction*. Endocrinology. 126. 31-8. 10.1210/endo-126-1-31. . A substitution of guanine by adenosine on the third intron of the rat growth hormone gene on the chromosome 10 is the cause of the phenotype Dwarf. This spontaneous mutation affects the 3 'splice / acceptor site (Rat By Database). The Dwarfs allele is inherited autosomal recessive.

Effects of dwarfism in rats

Sometimes Dwarf rats are referred to as suffering animals without stating any reason for this. Until now no health problems have been reported in pet dwarf rats. Rather, there is scientific evidence, that dwarf rats are less susceptible to developing tumors and have a longer life expectancy than standard rat. In a study, that compared SDR Dwarf rats with standard Sprague-Dawley rats, dwarf rats showed a higher life expectancy 20-40% in males and 10-20% in females. The endocrinology of dwarf rats is different than in starndard rats, Longevity and pathology, what makes them interesting as an animal model for aging research (Kuramoto et al. 2010 6)Kuramoto K1, Tahara S, Sasaki T, Matsumoto S, Kaneko T, Kondo H, Yanabe M, Takagi S, Shinkai T. (2010), Spontaneous dwarf rat: a novel model for aging research, Geriatr Gerontol Int. 2010 Jan;10(1):94-101). In another study, the SDR Dwarf rats showed an average 38% increased life expectancy compared to Sprague-Dawley rats. Lowered 8-oxo-2'-deoxyguanosine (8-oxodG), Marker for oxidative DNA damage, suppressed oxidative stress in the liver, the kidneys and the lungs has been found in dwarf rats. This was consistently accompanied by an increased activity of glutathione peroxidase enzyme. (Sasaki et al. 20027)Sasaki et al. (2002), Lifespan extension in the spontaneous dwarf rat and enhanced resistance to hyperoxia-induced mortality, Experimental Gerontology, Volume 48, Issue 5, May 2013, Pages 457-463). There is evidence, that dwarf female rats are less susceptible, to develop mamary tumors. In one study, the development of tumors in Dwarf rats and in rats, heterozygotus or homozygotus for the non-dwarf allele were, chemically induced. While the standard animals developed 4 Tumors per rat in average, dwarf rats only developed 0,21 tumors per animal in average (Swanson et al. 20028)Swanson SM1, Unterman TG. (2002), The growth hormone-deficient Spontaneous Dwarf rat is resistant to chemically induced mammary carcinogenesis, Carcinogenesis. 2002 Jun;23(6):977-82).

The standard of the Dwarf Rat

So far, only a standard for dwarf rats I know of has been developed. It was developed by Ratspac northwest in the US. There are two types:

  • Miniature: The rat shall conform to color, markings, and condition standards as for regular rats. May have a curious and busy personality. Body size should be 1/3 size of standard rats. The feet are shorter in relation to body. Tails are short in proportion to body size. Legs are short. The eyes should be large. he facial features of males may be more feminine, and this should not be faulted.
    Faults: Small standard rat, that is not genetically a dwarf rat
  • stocky: The rat shall conform to color, markings, and condition standards as for regular rats. May have a curious and busy personality. Body size should be 1/3 size of standard rats. The feet are shorter in relation to body. Tails are short in proportion to body size. The facial features of males and females are shorter and wider than the miniature Dwarfs. Eyes are very large and out of size proportion. The legs are short. Babies can have thin tails.
    Faults: Small standard rat, that is not genetically a dwarf rat

Are dwarf different than standard sized rats??

Amy from Camrattery, was one of the first breeders, who has worked with Dwarf rats in the private breeding program, She reported, that their Dwarf rats different from standard rat. she emphazised, that it would not be apporpriate, to refer to them as merely being a smaller versions of normal rats. She writes that her dwarf rats, are very anxious initially and tend to jump or run away, until they calm down at an age of about one year. Furthermore Dwarf rats are little bundles of energy. However, Amy also highlights, that Dwarf rats do not from other rats differ in terms of health from standrad rats. They do not have other or even more health issues..

Can dwarf rats- be kept together with standard rats??

This question can not be answered with a simple yes or no. If a socialization is succesfell, depends on the individual animals. Dwarf rats show the same territorial and agonisitic behavior as standard rats and communicate with them normally. They do not behave like babies or youngsters, who have not yet developed adult group behavior. On the other hand, dwarf rats cannot compete with an adult standard rat in strenght. When dwarf rats are integrated into a standard group, caution is advised and it should only be done under close supervision.

We keep our own Dwarfs with our standard rats and have had no problems so far.

Are Dwarf rats a breed that leads to suffering?

So far I have not found any information about physical or psychological changes in the Dwarf rat, which could lead to animal suffering. But on the contrary: There is evidence, Dwarf rats have a longer life expectancy and a lower lower inclination to tumors than standard rat. In the interpretation of § 11b of the Animal Welfare Act (German law) ("Breeds that lead to suffering in animals "Qualzucht")") notes regarding the dwarfism:

The cause of true dwarfism is a genetic weakness in growth with , generally proportioned underdevelopment of the whole body from birth on, which is not compensated by postnatal growth. In dogs, Rabbits and poultry is form of dwarfism is systematically been bred for in different races.

The expertice comes to the conclusion, that is the real dwarfism to no torment breeding, unless it causes the disposition to other diseases (with. B. disc prolapse, Hydrocephalus internus (hydrocephalus), persisting fontanelles, respiratory disorders, Deformity of bones and joints, and dystocia). None of these characteristics is given in Dwarf rats. In Germany many people believe that, dwarf females tend to have problems giving birth, I can not confirm this.

References   [ + ]

1. Robinson, R. (1965) Genetics oft he Norway Rat. Pergamon Press, Oxford
2. Rossin, A. M. and LAMBERT, W. V. (1934) A study of the inheritance and physiological behavior of dwarfism associated with an eye defect in rats. Proc. Iowa Acad. Be., 41: 317-18
3. WOOLLEY, G. W. and COLE, L. J. (1939) A new dwarf mutation (dw2) in Rattus norvegicus. Genetics, 24: 111
4. Seitaro Okuma (1984), Study of growth hormone in spontaneous dwarf rat, Nihon Naibunpi Gakkai zasshi
5. Takeuchi, Takashi & Suzuki, Hitoshi & Sakurai, Susumu & Nogami, Haruo & Reading, Shinichi & Ishikawa, Hiroshi. (1990). Molecular Mechanism of Growth Hormone (GH) Deficiency in the Spontaneous Dwarf Rat: Detection of Abnormal Splicing of GH Messenger Ribonucleic Acid by the Polymerase Chain Reaction*. Endocrinology. 126. 31-8. 10.1210/endo-126-1-31.
6. Kuramoto K1, Tahara S, Sasaki T, Matsumoto S, Kaneko T, Kondo H, Yanabe M, Takagi S, Shinkai T. (2010), Spontaneous dwarf rat: a novel model for aging research, Geriatr Gerontol Int. 2010 Jan;10(1):94-101
7. Sasaki et al. (2002), Lifespan extension in the spontaneous dwarf rat and enhanced resistance to hyperoxia-induced mortality, Experimental Gerontology, Volume 48, Issue 5, May 2013, Pages 457-463
8. Swanson SM1, Unterman TG. (2002), The growth hormone-deficient Spontaneous Dwarf rat is resistant to chemically induced mammary carcinogenesis, Carcinogenesis. 2002 Jun;23(6):977-82