Small Mammal Anatomy
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What is the order for rabbits, hares, etc?
What three suborders can the order Rodentia be split into? And which animals are in each suborder?
- Myomorpha - rat, mouse, hamster, etc
- Caviomorpha - guinea pig, chinchilla, degu
- Sciuromorpha - squirrel, chipmunk, etc
What is the order for ferrets, weasels, stoats, otters, badgers, etc?
Give three examples of small mammal cold adaptations (used during thermoregulation)
- High activity e.g. shivering
- Brown fat (which is more vascular and contains more mitochondria than white fat, meaning it will generate more heat)
- Peripheral vasoconstriction
Give four examples of small mammal heat adaptations (used during thermoregulation)
- Water conservation e.g. desert species are able to absorb more water through their digestive tract and produce more concentrated urine
- Peripheral countercurrent heat exchanges
- Size e.g. high surface-volume ratio, big ears, etc
Are rodents monophydont or diphyodont?
Monophydont - they only have one set of teeth
How many teeth do rodents have in total?
What is the dental formula of a rodent?
1-0-0-3 / 1-0-0-3
Why are rat incisors yellow?
Due to iron pigmentation
Rodent incisors are aradicular - what does this mean?
Their teeth are open rooted and so must be worn down continually.
What effect can poor husbandry have on open rooted teeth?
Poor husbandry i.e. failing to provide a knawing surface can lead to dental overgrowths, which in turn cause disease.
Why should you advise owners to monitor teeth after experiencing an incisor fracture?
If an incisor is fractured this causes a marked increase in the rate of growth meaning the teeth will grow at different rates so gnawing may not be enough to prevent overgrowth.
True or false: rodent molars are open rooted?
False - rodent molars have closed roots
Are rabbits monophydont or diphyodont?
How many teeth do rabbits have in total?
What is the dental formula for a rabbit?
2-0-3-3 / 1-0-2-3
Which teeth are commonly referred to as 'peg teeth' in rabbits and why?
The second incisors. These are rudimentary, smaller than the first incisors and situations behind them caudally.
What are the premolars and molars normally collectively referred to as?
The 'cheek teeth'
True or false: all rabbit teeth are aradicular?
True - they continually grow at a rate of ~2mm a week.
What is a key component of a rabbit's diet needed for sufficient teeth erosion?
Are ferrets monophydont or diphyodont?
What is the deciduous and permanent dental formulae for ferrets?
- Deciduous: 3(4)-1-3-0/3-1-3-0
- Permanent: 3-1-3-1/3-1-3-2
What are hamster cheek pouches?
They are distensible invaginations of lateral buccal endothelium.
How far do hamster cheek pouches extend back?
They extend back to the dorsocaudal scapula
How large can hamster cheek pouches get when they are full?
Up to 20mm
All small mammals are: monogastric or polygastric?
Monogastric - they have a single, simple stomach
Why is vomiting typically difficult in small animal species?
As the oesophagus enters the stomach at an oblique angle
What organs is the hind gut of a rabbit composed of?
The caecum and colon
How many gyral folds does a rabbit caecum have?
What is the difference between coprophagy and caecotrophy?
Coprophagy is the consumption of faeces. Whereas caecotrophy is the consumption of caecal pellets which are produced ~8hrs post feeding.
Why are caecal pellets good for rabbit health?
They have a high nutrient content and allow for efficient conversion of plant protein (70-80%).
What type of diet is required for the production of caecal pellets?
A high fibre diet
What effect does a) a low protein diet b) a high carbohydrate diet, have on rabbit health and caecal pellet consumption?
- a) A low protein diet encourages caecal pellet consumption
- b) A high carbohydrate diet decreases caecal pellet consumption and allows bacterial overgrowth in the caecum
Where do caecotrophs form?
In the caecum and proximal colon
How are caecotrophs normally ingested?
They are normally ingested directly from the anus through an anal reflex
Explain how you would tell the difference between a male/female rodent
- Male rodents have a rounded scrotum at the caudal end and copious fat around their testicles. They also have a longer anogenital distance than females.
- Females have a more pointed caudal end and a shorter anogenital distance.
Explain how you would tell the difference between a male/female rabbit
- Male rabbits have scrotal sacs either side of the preputial sheath and a circular genital opening
- Females have a triangular vulva and a slit-like genital opening. They also have thoracic and inguinal mammary glands.
- (Both have hairless patches lateral to the anus containing inguinal glands)
How long is oestrous in the a) rabbit b) guinea pig c) rat d) hamster?
- a) 5-6 days
- b) 15-17 days
- c) 4-5 days
- d) 4 days
How long is gestation in the a) rabbit b) guinea pig c) rat d) hamster?
- a) 31-32 days
- b) 59-72 days
- c) 21-23 days
- d) 15-18 days
How big is the litter size in the a) rabbit b) guinea pig c) rat d) hamster?
- a) ~6
- b) 1-6
- c) 3-18
- d) 5-10
How long does weaning take in the a) rabbit b) guinea pig c) rat d) hamster?
- a) ~4-7 weeks
- b) 21 days
- c) ~3-6 weeks
- d) 21 days
What common problem occurs in unneutered female ferrets that are not mated?
If unmated oestrogen production continues. This causes hyperoestrogenism which suppresses the bone marrow, decreases RBC production and causes post-oestrous anaemia
Why can catheterisation be difficult in male ferrets?
As their os penis has a curved tip
What is the correct terminology for ferrets that are a) male b) neutered male c) female d) neutered female?
- a) Hob
- b) Gib
- c) Jill
- d) Sprite
Why is respiratory disease rapidly debilitating in rodents and lagomorphs?
As they are obligate nose breathers
What two adaptations do rodents and lagomorphs have to support their high oxygen demand?
- They have low residual lung capacity
- They have a greater number of alveoli with a smaller diameter
Why can pneumonia spread quickly in rabbits?
As there is poor lobulation of the lungs in rabbits
The heart rates can range from ?-? in small animals?
State three possible sites for venipuncture in small animals
- Saphenous/cephalic veins
- Tail vein
- Marginal ear vein in rabbits
When can rabbit and guinea pig water intake increase?
It increases with anorexia e.g. due to dental disease
Rabbit and guinea pig urine is: acidic/alkaline?
Why does rabbit urine often have a creamy appearance?
Due to calcium carbonate
When might rabbit urine be red (but not due to the presence of blood)?
Due to plant pigmentation e.g. after eating beetroot
Rabbits have a high/low circulating calcium concentration?
How is most of the excess calcium cleared from the body in rabbits? How is excess phosphorus excreted?
- Calcium is excreted from the body via urine
- Phosphorus is excreted via faeces
True or false: calcium concentrations in rabbits are controlled mostly independent of vitamin D?
True (although chronic vitamin D deficiency can lead to mild hypocalcaemia)
What do ferrets suffering from adrenal neoplasia often present with?
When are rodents mainly active? Why?
At low light e.g. early morning and evening. As they are prey animals.
List some adaptations that help rodents have acute senses
- Large tympanic bullae
- Large olfactory bulbs
- Sensitive vibrissae (whiskers)
What type of glands are particularly present in rats?
Where are harderian glands located?
Behind the eye
What is the function of harderian glands?
They secrete lipids and a porphyrin red pigment which is involved in ocular lubrication and pheromones
When is secretion from the Harderian gland increased?
When the animal is stressed. This causes a red-brown deposit around the eye called chromodacryorrhea.
Why is it important to handle rabbits correctly?
As the rabbit skeletal system is very fragile and the spine is easily fractured if the rabbit is incorrectly held.
What is the spinal formulae for a) rabbits b) rats c) ferrets?
- a) C7, T12-13, L7, S4, Cd15-16
- b) C7, T13, L6, S4, Cd27-31
- c) C7, T15, L5/6, S3, Cd18
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