Table 3.

Signs of ageing in mice and recommended action.

Observation	General action to be taken (in non-shaded columns) – in consideration with the Project Licence adverse effects and humane endpoints, the expected phenotype of the animal and the needs of the intended research.a
	Initiate regular monitoring				Increase monitoring		Critical monitoring
Weight loss (compared to the animal's adult, stable weight)	Under 5%	Check teeth; look out for presence of other clinical signs and act accordingly	5–10%	As before; add pellets and/or wet mash every few days; weigh weekly	10–20%	Correct underlying causes if known and if possible; offer pellets/wet mash and weigh daily ensure the water nozzle is within easy reach, start to prepare to use the animal at an earlier time point	20%+	If body condition score is also low (e.g. 1 or 2), special justification normally required to keep the animal; otherwise cull
Weight gain (compared to the animal's adult, stable weight)	Above 5%	Check for possible internal tumours, ascites or impactions and act accordingly; if appropriate, offer opportunity for exercise (e.g. running wheel)	5–10%	As before, plus consider dietary or caloric restriction if appropriate and not already in place	10–20%	As before	20%+	Watch out for other signs associated with gross obesity (e.g. difficulty moving, impaired respiration) and act accordingly
Hair loss	Generalised or localised hair thinning	Look out for possible Barber and separate if skin becomes damaged	Alopecic (bald) patches	As before (if Barber); provide extra nesting material to help thermoregulation	Extensive alopecia	Ensure plenty of nesting material and facilitate nest building; ensure cage/nest is away from draughts	Generalised and extensive alopecia affecting most of body surface	As before; check skin remains in good condition
Ulcerative dermatitis	Small area of skin affected (<5 mm); mostly excoriation and erythema	Consider possible treatment(s) with EV (e.g. green clay + clip or file nails; fatty acid suppl; diluted chlorhexidine; silver sulfadiazine cream; dust free bedding)	Lesions of <3 mm affecting face or extremities; more extensive lesions over the body (0.5–1 cm)	As before; try a different therapy from the list of possibilities; monitor the condition daily	Lesions of >3 mm in face or extremities, extensive body lesions and/or clear discomfort	Consider last resort treatment(s) if appropriate, but preparation should be made to cull the animal; monitor daily	No clear improvement within 24 hours despite treatment	Cull
General appearance/coat condition	Grey hairs observed	No action required	Grey hairs; slightly dirty or unkempt or dry pelt; possible mild piloerection	Ensure adequate companionship to stimulate allogrooming; improve general condition (e.g. lower caloric intake, more exercise); if piloerection, investigate further (e.g. hypothermic?) and respond accordingly	Grey hairs; unkempt coat; piloerection; staining around penis/vagina	As before; if present, try to determine cause of piloerection and try to rectify; if other clinical signs are increasing in frequency, monitor daily prepare to cull	Very unkempt coat and marked piloerection; signs of incontinence	Cull
General appearance/colour	Slight paleness noted in feet or tail or eyes	Investigate possible causes and act accordingly; look out for other clinical signs; provide extra heat/nesting	Moderate paleness	As before; if possible and appropriate, use other diagnostic tests (e.g. imaging, blood sampling) to help determine cause(s); monitor daily and prepare to cull	Marked paleness	Cull
Spontaneous mobility – response to stimuli	Minor decrease noted in activity levels; slower to respond to stimuli	Perform more thorough examination and act accordingly (e.g. if arthritis involved, provide softer or deeper bedding; consider use of analgesics)	More obvious reluctance to move when cage lid removed or if prompted; less alert than normal	As before; if necessary and possible, carry out further diagnostic tests (e.g. imaging) to help determine cause(s); monitor at least weekly	Little voluntary activity noted; isolated from others	Monitor daily, provide additional heat and thoroughly evaluate any other possible clinical signs (e.g. pain? swellings?); if no clear cause or treatment solution available, prepare to cull	Unresponsive or very dull or clear signs of pain	Cull
Abnormal movement	Slow/stiff	Perform more thorough examination and act accordingly (e.g. if arthritis involved, provide softer or deeper bedding; consider use of analgesics)	Stereotypy; limp; slight head tilt	Investigate further and act accordingly (e.g. environmental changes to treat stereotypic behaviours)	Paresis; ataxia; worsening of some of the previous signs	If no clear cause/treatment solution available, prepare to cull	Paralysis, complete loss of limb function	Cull
Hunching	Slight hunched posture, possibly intermittent	Investigate possible causes and act accordingly	Moderate hunched posture, possibly continuous	Monitor daily, thoroughly assess possible causes and other clinical signs and act accordingly; prepare to cull	Markedly hunched posture	If no clear cause/treatment solution available or no response to previous treatment, cull
General behaviour (e.g. interaction with cage mates/use of bedding/nest making)	Minor departure from normal (e.g. less interaction with peers; some neglect of nest building)	Investigate possible causes (e.g. pain?) and act accordingly	Noticeable departure from normal (e.g. becoming isolated; more subdued or more aggressive)	As before and monitor daily	Significant departure from normal	If no clear cause/treatment solution available, prepare to cull	Unresponsive; very dull	Cull
Prolapse	Slightly protruding penis, vagina or rectum	Consider possible treatment/s with EV	More pronounced protrusion	As before if appropriate; otherwise consider termination	No resolution despite treatment/s; damaged organs	Cull
External lumps/masses	Small lumps/masses not affecting normal body functions	Consider possible treatment/s with EV if appropriate	Medium-size (0.5–0.8 cm) lumps/masses	As before; check for possible presence of other internal lumps and/or other clinical signs; monitor body condition score weekly	Large lumps (0.8–1 cm); ulcerated or infected	If no clear cause/treatment solution available, prepare to cull	Lumps/masses > 1.1 cm or affecting body functions /mobility	Cull
Internal lumps/masses (impacted seminal vesicles can become quite large and yet cause no apparent ill-effects)	Small palpable lumps/masses not affecting normal body functions	Consider possible treatment/s with EV if appropriate; check for other possible clinical signs	Medium-size (<0.5 cm) lumps/masses	As before; consider the possible use of other diagnostic tests (e.g. ultra sound imaging); monitor body condition score weekly	Large lumps (>0.5 cm); concurrent presence of other clinical signs (e.g. pallor)	If no clear cause/treatment solution available, prepare to cull	Large lumps/masses affecting body functions or causing other significant clinical signs	Cull
Eye defects	Defects unlikely to affect normal body functions and behaviour (e.g. cataracts, one missing eye, conjunctivitis, small eye)	Consider possible treatment(s) with EV if appropriate; check for possible behavioural changes or other clinical signs	Defects likely to result in pain or affect normal body functions (e.g. swollen, closed eye; protruding eye)	Monitor daily	Defects clearly affecting normal body functions or behaviour (e.g. ulceration)	If no clear cause/treatment solution available or no response to previous treatment, cull	Signs of pain that cannot be controlled	Cull
Abnormal respiration	Slight departure from normal (e.g. slight increased or decreased respiratory rate; intermittent change; cough/sneeze)	Thoroughly evaluate possible causes with EV and act accordingly	Moderate departure from normal or more persistent changes	Monitor daily and check for presence of other possible clinical signs	Significant departure from normal (e.g. laboured breathing; nose bleeding; rapid shallow breathing)	If no clear cause/treatment solution available or no response to previous treatment, cull
Abnormal stools	Slightly softer than normal faeces; slight staining around anus	Thoroughly evaluate possible causes and act accordingly; provide clean bedding	Soft stools; stained perineal area	As before; check for presence of other possible clinical signs	Persistent diarrhoea; stained perineum; blood-stained stools	If no clear cause/treatment solution available or no response to previous treatment, cull

^aNB. Always use in partnership with the EV and bear in mind that allowing animals to display many of the signs in this table will likely require specific legal authorisation.

EV: establishment's veterinarian.