Small Mammals - Rodents Flashcards
Describe the taxonomy of rodents and what are they classified by
Taxonomy: Kingdom - Animalia Phylum - Chordata Class - Mammalia *Order: Rodentia*
Classified by having continuously growing incisors
What is the smallest and largest rodent?
Smallest - African pygmy mouse and Pygmy Jerboa 3g
Largest - Capybara 50-60 kg
How many orders is the rodents order divided?
5
List the rodent sub orders and give examples
- Myomorpha - mouse like: mice, rate, gerbils, hamsters
- Hystricomorpha - porcupine like: guinea pig, chinchilla
- Scuriomorpha - squirrel like (chipmunks)
- Castorimorpha - beavers, gophers, kangaroo mice, pocket mice, kangaroo rate
What should you never use when reducing crown length and why?
Nail clippers!!!!
- Can split the tooth along the length as teeth are brittle
- therefore they can easily fracture causing pain and discomfort
Why is it important to know the body weight and life expectancy
BW - drug dosage - often scales not designed to weight such small animals
LE - helps with prognosis and decision making e.g. end of life span therefore different treatment?
What are the important “pet suborders” and e.g
o Myomorpha - mouse like: mice, rats, gerbils, hamsters
o Hystricomorpha - porcupine like: guinea pig, chinchilla, degu (diff from all others so big debate)
Life expectancy
- mouse
- rat
- hamster
- gerbil
- guinea pig
- chinchilla
- 1-2.5 years
- 3 years
- 1.5-2 years
- 1.5-2 years
- 4-7 years
- 10-15 years
Bodyweight
- mouse
- rat
- hamster
- gerbil
- guinea pig
- chinchilla
- 20-40 g
- 400-800 g
- Syrian 100-200 g Russian 20-40 g
- 70-130 g
- 750-1000 g
- 400-500 g
Dentition Myomorpha
I= 1/1 C = 0/0 PM = 0/0 M = 3/3 x 2 = 16
Dention Hystricomorpha
I= 1/1 C = 0/0 PM = 1/1 M = 3/3 X2 = 20
Describe the incisors
Open rooted, continuously growing
Describe molars
Open rooted preM and M
Talk about the cheek teeth of Myomorphs and Hystricomorphs
- Myomorph = cheek teeth erupt continuously for short period of time, then STOP erupting. Very rare to get dental disease of molars and pre molars
- Hystricomorphs cheek teeth = continuously erupt so likely to have issues e.g. with overgrowth
Describe the mouth anatomy of rodents
o Large diastema (gap between incisors and cheek teeth) o Can GNAW without wearing molars or swallowing debris o Lower jaw moved forward o Incisors opposed but molars apart o Cheeks drawn into diastema o Can CHEW o Lower incisors behind uppers o Molars opposed
What type of INCISOR teeth do rodents have?
Aradacular Eledont
Open rooted continually growing
Describe rodent Incisor teeth
Why don’t swallow when gnaw
- Chisel shaped incisors
- Lower incisors are about 3 X longer than upper (don’t mistake for overgrowth!)
- They can gnaw without swallowing debris as cheeks come together when bottom jaw forward
Why are rodent teeth chisel shaped?
o Hard enamel on one side (rostral)
o Softer dentine wears more quickly, resulting in chisel shape forming
o So as chew, back of tooth wears faster – sharp teeth
What type of molars do rodents have? and what deos it mean?
- hystricomorphs, the premolars and molars are ELODONT
- means continue to erupt throughout life, dental disease common - myomorphs the molars are ANELODONT
- Means M overgrowth uncommon
What other animals have similar molars to hystricomorphs?
Horse and rabbit - continue to grow throughout life! therefore these animals are also prone to dental disease
Talk about the gastrointestinal system broadly
- Mono gastric
- Relatively large caecum
- Elongated colon
Do rodents exhibit caecotrophy?
Most species do!
Reingesting faeces to enahnce the uptake of essential vitamins adn AA in hindgut
Why do rodents have a relatively large caecum?
- Hystricomorph are herbivores
- Myomorphs are omnivores
- So a large caecum helps to utilise some bacterial digestion of plant material
Can rodents vomit?
NOPE!
- Strong oesophageal sphincter (cardiac) and crural sling
- limiting ridge between oesophagus and cardia of stomach
- Diaphragmatic muscle is too “weak” to support emesis (vomiting)
Interesting fact need to do before surgery
- Don’t need to starve as have a high metabollic rate and relatively fast gut transit time.
- poisons are good as once ingested are absorbed relatively quickly, and can’t vomit!
Broadly describe the respiratory system
- Obligate nasal breathers
- Lungs: 4 lobes
Left lung ahs a single lobe, right 4 (cranial, middle, caudal, intermediate - but hamsters have an additional lobe caudal accessory (5 in total)
Why are rodents obligate nasal breathers?
- due to high larynx and long epiglottis
2. means passage straight from trachea to nasal cavity, preventing mouth breathing in normal animal
How is respiration optimised?
o Short airways and increased respiratory rates (breath in faster)
o More alveoli of thinner diameter (increased S.A for gas exchange)
o High chest wall compliance = increase vital capacity (take in more air in each breath), decrease residual lung capacity (when breath out, everything taken out)
o Optimised to expand lungs and efficiently expel air
Oxygen dissociation curve - where are small animals vs larger?
Smaller animals move to right, harder for oxygen to bind but easy to release
Hb releases O2 more readily at tissue level
How do rodents maintain thermoregulation cold
Behavioural
o Huddling, nest building, tunnelling underground where temp fluctuates less)
• Shivering
• Peripheral vasoconstriction (tails, ears, paws) keep heat in core
• Non-shivering thermogenesis
o Brown fat behind scapula, round neck and shoulders. Can persist for life
What is heat adaption for rodents
- Few sweat glands (minimal on feet)
- Evaporation of saliva that is groomed over body (evaporative heat loss)
- Arteriovenous shunts in ears, tails & feet
Broadly describe Myomorph and hystricomorph reproductive strategies
Myo 1. large litters 2. short gestation 3. Altricial young (blind deaf, no fur) Hystrico 1. Smaller litters 2. long gestation 3. precocial young (ready to go with fur)
What sort of ovualtors are rodetns?
- all are polyoestrus sponstaneous
2. apart from chinchillas whoa re poly oestrus seasonal - want young to be born at most optimal time
Gestation of:
- mice
- rate
- hamsters
- gerbils
- guinea pigs
- chinchillas
- mice - 19-21 days
- rate - 21-23 days
- hamsters - 15-18 days
- gerbils - 23-26 days
- guinea pigs - 59-72 days
- chinchillas - 111 days
Age of sexual maturity of rodents
mice, rate, hamsters, gerbils = 6-8 weeks
Guinea pig = 4-6 weeks
Chinchilla - 8 months
Female rodent uterus
Bicornuate: guinea pig, ferret, dog, cat (single cervix, small body, long horns
Duplex: hamster, rat, mouse, chinchilla, rabbit (2 cervix)
If ever do a c section of a animal with duplate cervix you have to do 2 incisions, one on either horn as can’t milk offspring from one side to other
Why type of penis do male rodents have?
What can they do with testes?
Os penis like dog
2. they have an open inguinal canal so can retract testes back into abdomen
What is interesting about chinchilla testes?
- testes are often inguinal unlike others that descend into scrotal sac following puberty
Name the accessory sex glands of the male rodents
o Seminal vesicles o Prostate o Coagulating gland o Bulbourethral gland o Preputial gland o Mucous plug into vaginal to help with intromission
How do you sex rodents and what do you need to know when doing so?
- know that is is pretty stress inducing
- Ano genital distance - longer in males than females
- mice and rats - only females have nips
Gerbils and hamsters both sexes have nips, but more obvious ones in females
Guineapig both have obvious nips! - male gerbil has a much larger ventral scent gland (bald path on abdomen)
- Male hamsters - lump
- Male guinea pig (boars) looks like I and penis can be everted using gentle pressure
- Female looks like a y
- Chinchilla dont mistake clitoris for penis!
What are the 4 distinct periods of female reproductive cycle
o Proestrus
o Oestrus
o Metoestrus
o Dioestrus
What is the copulatory plug?
- Found following copulation in most female rodent species
- Thought to be congealed sperm, mucus and accessory ejaculatory fluids, which harden within the cervix
- Remains in place for 8-12 hours
- Often found on cage floor rather than in vagina! – hard waxy
- Thought to seal vagina and make it more likely for mating to be successful
• High surface area to body weight means susceptible to
o Dehydration
o Hypothermia
o Hypoglycaemia
o Have to consider when doing any procedure on them
• Fast metabolism
o Increased O2 consumption and increased food intake
o Husbandry very important
• Constantly growing molars in GP’s and chinchillas
- Larynx high in oropharynx
- Coprophagy is normal
o Susceptible to dental disease
– obligate nose breathers
– vitamin recycling
Individual species features of rat
Naturally nocturnal
Yellow incisors due to iron pigment – normal
Prominent harderian gland
o Red brown gland fills large part of orbit and lies behind the globe
o Increased secretion when stressed or unwell
o Looks like blood but NO!
Venupuncture sites – take <1% bodyweight
o Lateral tail vein
o Lateral saphenous
o Ventral tail artery
No gall bladder
Urethral orifice separates from vulva
Extensive mammary tissue from axilla to groin in females
o 6 pairs of mammary glands
o Prone to tumour formation
o Mammary fibroadenoma – benign, can remove and be successful
o Mammary adenocarcinoma – malignant
Individual species features of chinchilla
• Naturally nocturnal, but can adapt to diurnal lifestyle
o Need 12hr:12hr light dark periods
o If cycle differs such, often get problems
• Very dense fur – 50-60 hairs from each follicle
o Tolerant of cold (but not wet) and sensitive to heat
o Will ‘drop’ coat if stressed, careful handling required (fur slip) as a vet handle carefully
o Dust baths help maintain coat condition
• Long gestation period (111 days)
o Young precocial fully formed and ready to go
• Blood sampling
o Cranial vena cava and lateral saphenous
Interesting species facts about Guinea pig
• Absolute requirement for vitamin C
o 10mg/kg/day (3 times this so 30mg/kg/day if pregnant)
o Scurvy can develop within 4 days of decreased intake
• Males have prominent caudal sebaceous gland
• Pubic symphysis dilates to allow parturition, important to breed females before age of 7-8 months to prevent fusion and subsequent dystocia. If want to breed older animal with no litter prior warn for dystocia
• Blood sampling
o No tail so
o Cranial vena cava
o Jugular
o Femoral or lateral saphenous vein
• Thymus is cervical
o Often used in laboratory science
• Young – precocial! Pregnant for 63-65, like dogs
Interesting species facts about Gerbils
• Form monogamous pairs
o Dad helps with raising young
o Post mating vaginal plug deep and not easily seen
• Both sexes have large ventral midline sebaceous gland
o Larger in males
o Not a tumour, however, is a site for tumour formation
• Drink very little (4ml/100g/day), are desert species and have excellent urine concentrating abilities. Popular pets as not too smelly
• Avoid handling by tail – can slough, skin can just fall off
• Absolute requirement for vitamin C
o 10mg/kg/day (30mg/kg/day if pregnant)
o Scurvy can develop within 4 days of decreased intake
• Males have prominent caudal sebaceous gland
• Pubic symphysis dilates to allow parturition, important to breed females before age of 7-8 months to prevent fusion and subsequent dystocia
Interesting species facts about Hamsters:
Bilateral cheek pouches which can extend caudally as far as the shoulder blades - primary function storage adn transport food
o Often site of impaction – you will need to go in and clear out
o Lined with oral mucosa
o Immunologically privileged site
o can inflate - keep afloat
• Stomach is compartmentalised into
o Forestomach (like ruminants)
o Glandular stomach
• Sensitive to antibiotics due to bacterial population
o Disruption of normal gut flora
• Females have separate vaginal and urethral openings
• Bilateral vaginal pouches internally making vaginal cytology hard to interpret
o Vaginal plug deep and difficult to see
o See post mating vaginal discharge
• Shortest gestation of all eutherians
o 15-18 days (Syrian)
• Flank glands – androgen responsive. Litke ventral scent gland in gerbal, similar appearance
o More obvious in males than females
o Often mistaken for tumours
• Blood sampling tricky
o No tail vein!
o Use jugular, cephalic, cranial vena cava
• Will enter state of hibernation
o If temperature drops below 5C
• Nocturnal but very active during hours of darkness can travel around 5 miles in one night!
• High water consumption
o Up t0 20ml a day in some large adults
