As a rescue, we pride ourselves on staying up-to-date on the latest advice and scientific research around hamsters and their care. Many of the scientific findings are taken from studies performed on rodents in the interest of improving our understanding of human healthcare.
“The increase of rectal temperature and the fever index were the highest in animals housed in large cages and the smallest in animals housed in small cages. Through cage enrichment and increasing cage size the mean febrile response increased while the mean baseline rectal temperature decreased.” [Kuhen, G. 1999]
The above 1999 study is one of the few scientific studies that properly looked into the benefits of a larger, more enriched enclosure for hamsters. The recommended minimum size enclosure for all species of hamster is now 100x50cm unbroken floor space, which is equal to 5,000sqcm or 775sqin.
“All 10 males (P¼0.001 on a binomial test)and eight of 10 females (P¼0.0547) ran more in the large wheel than in the small one during the first 20 days. The preference was very clear for males: on average they ran 86717.8% of their total daily mileage in the large wheel.” [Reebs S.G. and St-Onge P. 2005]
The above 2005 study is another of the few scientific studies performed for the welfare of hamsters. Reebs and St-Onge proved a direct preference for larger wheels in hamsters.
“Hamsters with plastic mesh inside their wheels took longer to develop wounds but once they appeared, the wounds were larger and lasted longer.” [Beaulieu A. and Reebs S.G. 2009]
The above 2009 study was performed to show the link between running surfaces of wheels along with adverse textures of bedding material and wound development on the paws of hamsters. Beaulieu and Reebs proved that mesh surface wheels caused larger and longer-lasting wounds.
Advice on choice of bedding material
“Significant preferences in the first experiment were: pine shavings over aspen shavings, corn cob over wood pellets,pine shavings over corn cob and aspen shavings over wood pellets (aspen shavings versus corn cob was not tested). However, there was no significant preference expressed in the second experiment, suggesting that the general preference for shavings in the first experiment was based on bedding material suitability as a nesting material.” [Lanteigne M, Reebs SG. 2006]
A preference was found in the above 2006 study for softer shaving-based bedding over wood pellets, as hamsters appeared to use it to build a 'nest'. This study supports our recommendation of paper-based bedding, as it is typically softer than shavings, but safe wood shavings - aspen, birch, etc. are a great option especially for creating burrows. Pine and cedar woods are not safe; this will be expanded on later.
Advice on bedding depth
“Hamsters kept with 10 cm deep bedding showed significantly more wire-gnawing and a higher running wheel activity than the hamsters in the other groups. In 80 cm deep bedding wire-gnawing was never observed. Stressor application showed no significant immediate influence on behaviour. All hamsters in 40 and 80 cm bedding constructed burrows which they occupied. The body condition (body weight/body size3) was significantly higher in the animals kept in deep (80 cm) compared with those housed in low (10 cm) bedding cages.”
“Like their wild-living relatives, captive hamsters dig burrows into the soil, if given the opportunity (Dieterlen, 1959) and if nesting material and bedding are missing, hamsters become aggressive and stop eating (Lochbrunner, 1956). In mice, digging was found to be of similar importance as food and water (Sherwin et al., 2004). The Swiss Animal Protection SAP (Schweizer Tierschutz STS) discourages owners to use pre-fabricated artificial burrow systems (plastic tubes such as Habitrail) because of their poor ventilation and the restriction of performing natural digging behaviour (STS Leaflet). They recommend a minimum bedding depth of 30 cm.” [Hauzenberger AR., Gebhardt-Henrich SR, Steiger A. 2006]
The above 2006 study shows an incredibly important link between stress in hamsters and bedding depth, leading to the ability to burrow. Aggression was even found in those hamsters missing nesting material and bedding. The recommended bedding depth as a result is 30cm, or 11in. We recommend a minimum depth of 8in across at least 2/3 of the enclosure with at least 4in/a full base across the rest of the enclosure. This displays why the height of the enclosure is important for hamsters, so the appropriate amount of bedding can be provided along with all accessories.
Advice on Kapok bedding
The following 2021 study shows the genuine dangers of using ANY form of fluffy/fibrous bedding, including Kapok bedding. The main risk of ingesting this bedding is intestinal obstruction obstruction.
“Intestinal obstruction may occur following ingestion of bedding material. In general, paper bedding or shavings are recommended (Keeble, 2009). A depth of at least 40cm allows burrowing behaviour and improves welfare of Golden hamsters (Hauzenberger et al, 2006). Inappropriate bedding can lead to intestinal impaction and obstruction. Figure 5 shows a dilated large intestine found at post-mortem of a hamster presenting initially with diarrhoea, followed by reduced/absent faecal production, dehydration and abdominal pain.” [Baldrey V. 2021]
“For the purposes of welfare assessment, the addition of environmental enrichment has been the most common positive manipulation in judgement bias studies. The majority of studies where enrichment was added reported a positive shift in judgement bias.” [Bethell EJ, Koyama NF. 2015]
The above 2015 study performed a test on hamsters to see if they would be more likely to approach an object if there was something next to it or not. All hamsters in the study approached the object faster with something next to it than when it was by itself.
“Such teeth are characteristic of animals that have a diverse diet.” [Hubrecht RC., Kirkwood J. 2010]
Hamsters' teeth were found to be characteristic of animals who have a diverse diet, proving that feeding pelleted food only would not be enriching for them. We recommend food mixes with a minimum of 20 ingredients as a result.
Advice on garlic
“Other target organs damaged during high exposure include the gastrointestinal tract: Aloe vera and Senna; kidney: Aloe vera, raw Garlic, Ginkgo, Kava kava, Pulegone, St John's wort, and Tobacco; heart: Ephedra; and the vascular system: Riddelliine pyrrolizidine alkaloid and Tobacco.” [Kathleen M. Heinz-taheny KM., Rudmann DG., Mahler BW. 2023]
The above research has shown that the kidneys can be damaged through exposure to high levels of garlic. The following will suggest health benefits, however again this is only achieved through consumption of large amounts. Our recommendation based on these contradictory studies is to err on the side of caution, and not feed your hamsters garlic, as the potential health risks and benefits cancel one another out.
“Administration of a combined dose of tomato and garlic significantly decreased the incidence of HBP carcinomas and mean tumor burden and the frequency of bone marrow micronuclei. . .The present study, an extension of our previous work, demonstrates the efficacy of the combina- tion in modulating xenobiotic-metabolizing enzymes and the increased frequency of bone marrow micronuclei. To- gether, these findings substantiate the antigenotoxic and anticarcinogenic effects of tomato and garlic reported by us and other workers.” [Bhuvaneswari V, Abraham SK, Nagini S. 2005]
The 2005 study references the medicinal qualities of a combination of tomato and garlic on cancerous tumours and related ailments. If your hamster has cancer, please consult your exotic veterinarian before administering at-home treatments, as the 2023 study suggests that it could even cause more harm than good.
Advice on milk
“In short-term studies (7 to 90 days), AFB1 shows multiple negative effects in rodents, including in-hibition of normal growth, liver and kidney damage, as well as sustained alterations in the intestinal microbiota. AFB1 is a genotoxic and carcinogenic substance. There is evidence of genotoxic effects in pregnant mice, foetuses and young animals. Unlike AFB1, there are fewer studies available on the genotoxicity of other aflatoxins. Epidemiological studies reported since 2006 reinforce evidence that exposure to aflatoxins is associated with a risk of developing hepatocellular carcinoma, with an increased risk for people infected with hepatitis B (HBV) and C (HCV) viruses.” [Muñoz, M.J.G. et al. 2023]
The above 2023 study references the potential dangers of consuming too much milk and hazelnuts; carrier foods for aflatoxins for rodents - particularly mice and rats. The following 1992 study provides an explanation as to how a hamster's gastric pouch allows them to consume milk while rats and mice are still at risk. Hamsters are not lactose-intolerant creatures, so very small amounts of milk can be considered safe. The risks of ingesting calcium, however still apply.
"The hamster’s pregastric pouch is similar in both structure and function to the rumen of herbivores. It is likely that the ruminant type microorganisms residing in the pregastric pouch, like those of the rumen of herbivores, rapidly attack and digest water soluble carbohydrates such as lactose, thereby minimizing the amount of ingested lactose that reaches the small intestine intact and sparing hamsters the negative consequences of lactose ingestion that are typically experienced by monogastric animals such as rats.” [DiBattista D. 1992]
Advice on citrus fruits (lemon)
The following studies discuss the potential health benefits and risks of citrus fruits for rodents. Most of the data in these studies was gathered for the benefit of human health, and refers to chronic consumption and high amounts of the flavanoids being ingested in order to present with risks or benefits for the hamster.
“The data show that 4 flavonoids (hesperetin, neohesperidin, tangeretin, and nobiletin) were inactive. The results with naringin and naringenin show that both of these flavonoids significantly lowered tumor number [5.00 (control group), 2.53 (naringin group), and 3.25 (naringenin group)]. Naringin also significantly reduced tumor burden [269 mmm3(control group) and 77.1 mmm3(naringin group)]. The data suggest that naringin and naringenin, 2 flavonoids found in high concentrations in grapefruit, may be able to inhibit the development of cancer.” [Miller EG. et al 2008]
“The results of this study suggest that lemon peels and the waste stream of the lemon peels are as effective in lowering plasma and liver cholesterol in hamsters as the pectin extracted from the peels and that also compounds other than pectin are probably responsible for the cholesterol lowering effect of the citrus peels.” [Terpstra AH et al 2002]
It should be noted that plasma and cholesterol levels should be managed through a hamster's consumption of a proper diet, consisting of a seed mix along with animal and vegetable proteins, nuts, flowers and occasional fresh fruit and vegetables. Any methods to lower cholesterol and/or plasma in hamsters should be under exotic veterinary instruction. They will often suggest probiotics.
“The importance of cumin and lemon plants in the prevention and reduction of diseases caused by the high level of harmful fats in the body, such as heart disease and arteriosclerosis due to the high capacity of plants to scavenge free radicals by the action of their active compounds and that hypercholesterolemia has a negative effect on the tissues of some organs for male rats, such as the aorta.” [Ahmed Mejbel E, H Ali L. 2022]
The 2022 study above shows the potential risks involved with administering lemon and cumin in order to cure high levels of cholesterol, as it can lead to negative impacts on the aorta.
Advice on seeds/sprays
“Based on the vital results from this study, hamsters fed a HFCD formulated by an addition of FX had lowest serum lipids and best serum cholesterol profile when compared to those fed HFCDs formulated by an addition of CO or BU. In the gene expressions of cholesterol homeostasis in hamsters, the LDL-receptor expression in the FX group was higher than other HFCD groups which resulted in lower serum cholesterol levels.” [Tzang BS. 2009]
The above study proved that flax seed (FX) is a completely safe ingredient to reduce cholesterol levels in hamsters. This can be given in seed or spray form, and milled flax can be baked into cookies or other treats for your hamster. The following study will show the benefits of amaranth - which can be given as a seed spray - in lowering cholesterol in hamsters.
“Amaranth grain and oil decreased very low-density lipoprotein (VLDL) cholesterol by 21–50%; and increased fecal excretion of particular neutral sterols and the bile acid ursodeoxycholate.” [Berger A. 2013]
Advice on onion
“A study by Selmi et al. showed that chronic administration of malathion caused enlargement of sinusoids, mononuclear cell infiltration, dilatation, haemorrhage and necrosis of rats' liver tissues.” [Severcan Ç, et al. 2019]
The above study discusses the harmful effects of an increased intake of malathion, which is found in onion and cauliflower. Cauliflower can be given in small amounts, while the acidity of the onion can have negative impacts on the digestive system.
Advice on seafood
The following study has some intriguing insights into the effects of fish/seafood on preventing hamsters going into a state of torpor.
“Interestingly, a subgroup of hamsters which never entered torpor but remained euthermic throughout winter displayed a phenotype similar to animals in summer. This was characterized by lower proportions of LA and increased proportions of DHA in SR membranes, which is apparently incompatible with torpor. We conclude that the PUFA composition of SR membranes affects cardiac function via modulating SERCA activity, and hence determines the minimum Tb tolerated by hibernators.” [Giroud S. et al. 2013]
The 2013 study suggests an incompatibility between torpor and Docosahexaenoic acid, which can be found in a variety of seafood, including tuna and salmon, which are safe to give to hamsters once cooked. This is due to the acid not allowing the heart rate of the hamster to lower to the necessary Tb to go into a state of torpor. We're researching further to see whether giving small amounts can make an impact on the chance of the hamster entering torpor.
Advice on meats
The following information simply provides supporting evidence that by providing regular vegetables and animal-based proteins (primarily meats - we recommend boiled plain chicken), it can reduce the risk of heart conditions through reducing the risk of cardiomyopathy, which increases the thickness of the heart's chambers, resulting in stiffness and lowers the efficiency to pump blood around the body.
“Cardiomyopathy resulted in a depletion of vitamin E, creatine, carnitine, taurine and coenzyme Q10. Supplementation resulted in improved cardiac ultrastructure, function and contractility compared with nonsupplemented hamsters.” [Keith ME. et al. 2001]
Advice on length of pregnancy watch
“Lactational embryonic diapause is a common reproductive phenomenon best understood in the mouse. Embryonic diapause in rodents can last from 1 day to several weeks, with the length of delay depending on the number of sucking young (Weichert, 1940, 1942; Mantalenakis and Ketchel, 1966; Pritchett-Corning et al., 2013). Reactivation from diapause then occurs after removal of the young, resulting in a surge of oestrogen (Fig. 2) (Psychoyos, 1973).” [Renfree MB. 2017]
The above study considers the effects of embryonic diapause, which is something that is understood to be possible in the majority of rodent species, but most widely observed in mice and rats. The pregnant hamster in question must have given birth to a prior litter, which could lead to them 'pausing' their pregnancy on day 3.5, as lactation suppresses the necessary hormones for a viable litter. This is an incredibly rare occurrence, and there is no literature supporting that hamsters could 'hold in' the pups once developed, and the pups would have continued to develop following the removal of suckling young from the mother. The delay has been observed to last a maximum of 6 weeks in mice from the last point of contact with a male.
“An additional factor that appears to influence blastocyst reactivation is PAF, a phospholipid that signals via its receptor platelet-activating factor receptor (PTAFR). Both PAF and PTAFR are present in the endometrium and embryos of mice, rabbits, hamsters, humans and marsupials (O'Neill, 1985, 2005; Ammit and O'Neill, 1991; Jin and O'Neill, 2011; Kojima et al., 1993). The release of endometrial PAF is under the control of progesterone and oestradiol (Chami et al., 1999; Li et al., 1999). It stimulates embryo metabolism, enhances cell proliferation and increases overall embryo viability (Emerson et al., 2000; O'Neill, 2005).” 
The 2017 study shows that hamsters possess the necessary factors to support embryos in a state of diapause, and to bring them out of it with no reduction of litter size or harm to the embryos.
Due to the rarity of embryonic diapause in rodents, we will not be increasing our standard pregnancy watch period for any species of hamster. If a dwarf or roborovski hamster comes to us having recently given birth and we know they had contact with a male in the day/s since giving birth, we will extend their pregnancy watch to up to 6 weeks, as this is the only natural known cause of diapause in rodents.
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