Chapter 4 Small rodents
Small rodents are popular both as children’s (and adult) pets, but also as show animals. Rats in particular have a very enthusiastic following. Those species that are likely to be encountered in the veterinary surgery are:
Small rodents are prey animals and may become stressed by the presence of potential predators such as cats, dogs and unfamiliar people; this includes auditory and olfactory signals, so where possible they should be housed separately from such animals, and hands should be well cleaned to remove other species’ odours before handling.
Many small rodents move quickly and unpredictably and care should be taken to prevent unwanted escapes or potentially disastrous leaps to the floor. Gently wrapping in a towel will often help with the handling and control of an excitable rodent. A sure way to annoy a pet rat (and alienate its owner) is to attempt to grasp it by the scruff of the neck. Most are used to being gently handled and are unlikely to bite. If in doubt, use a towel. Do not attempt to pick a hamster straight from its bed; they are territorial of this and are likely to bite. Instead, gently tease or tip it out. Recalcitrant hamsters are more easily scruffed and, although this will help with an examination of the teeth, it may upset the rodent.
Hamsters are permissive hibernators and may attempt hibernation if temperatures fall consistently below 4.5°C. Poor food availability, altered photoperiod and other factors may also induce hibernation, although this varies between individuals. Hibernation is not continuous but is interrupted every 2–3 days by bouts of normal activity including foraging. During hibernation, hamsters remain sensitive to tactile stimulation and can be gently aroused. Exposure to normal room temperatures (18–22°C) and lighting (12–14 h) are unlikely to trigger hibernation. Many owners misinterpret clinical signs of illness (lack of movement and lethargy, anorexia) with hibernation, often delaying presentation to the veterinary surgeon.
Small rodents by virtue of their size and the high risk of predation are forced to obtain most of their water from preformed (food) and metabolic sources. Dehydration can be a real issue, especially at higher environmental temperatures (Table 4.2).
|Intravenous (rat and mouse)||Lateral tail vein (helps if warm!) (Fig. 4.1)|
|Intravenous (hamster)||Very difficult: lateral tarsal vein, anterior cephalic vein and lingual vein|
|Intravenous (gerbil)||Lateral tail vein or saphenous vein|
|Intraperitoneal (all three species)||Hold the patient vertically downward and inject into the lower left quadrant|
|Intraosseous (all three species)||Under GA to insert either an intraosseous catheter or a hypodermic needle into the marrow of either the femur (via the greater trochanter) or tibia (through the tibial crest). Fluids, colloids and even blood can be i.o. if necessary.|
Jugular catheterization can be attempted in all species but it is difficult and may result in respiratory embarrassment. Many of these sites may also require anaesthesia and surgical cut down, which may not be appropriate for the welfare of the patient. In hypovolaemic patients vascular access may be impossible. It is better to consider either i.p. or i.o. administration.
Much endogenous body heat is generated by gut and muscle activity; sick, inactive or anaesthetized rodents are prone to hypothermia (Jepson 2004). Use a heat source, e.g. electric heat mat, plus insulation such as silver foil over the feet, pinnae and tail (reduces heat lost by conduction) and bubble wrap (reduces heat lost by convection). Maintain in warm air, e.g. incubator, or use a commercial medial warm air generator.
Many small rodents are presented as emergencies after a prolonged period of ill-health that will have affected their food intake. These animals are often hypoglycaemic – testing with a commercial glucometer on a small sample of blood – and i.v. or i.p. glucose can be given to these cases once identified.
It is important to keep small rodents warm as they have a large surface area compared with volume, which results in significant heat loss during surgery. This also applies during anaesthesia – hypothermia acts as a general depressant and is also immunosuppressive. Merely applying insulation such as bubble wrap is often insufficient – inactive, anaesthetized rodents are not generating heat and you may be insulating it from a higher ambient temperature. Place these animals on to a heat mat, on to which is placed an absorptive towel or other material to both protect the mat from becoming wet, and reduce the slight risk of localized burns.
Syrian hamsters have large, bilaterally symmetrical hip glands; these are scent glands used for marking burrow walls and in males they can be particularly pronounced in both size and the amount of sebaceous secretion they produce. These are frequently mistaken as skin lesions. Dwarf hamsters and gerbils possess ventral scent glands visible on the abdomen.