as motor deficits or anorexia) and should be trained to recognize them. Additional training of the animal-care staff to include practical information on the special needs and common problems associated with specific strains is recommended.
The dramatic growth in the use of genetically modified rodents, primarily mice, creates substantial challenges for timely and effective assessment of animal health and well-being. Many institutions house large populations of genetically modified mice with a wide array of deficits that affect physiologic homeostasis and behavior. The popularity of high-density, individually ventilated caging systems for housing these valuable mice adds barriers and challenges for effective observation and increases the importance of a careful and systematic examination of individual animals during scheduled cage-maintenance activities.
The general health of novel genetically modified animals should be assessed soon after their availability and before the onset of complex behavioral analyses (Crawley, 1999). Identifying potential health problems early is critical to providing appropriate care. Undetected health problems can also skew the assessment of more complex behaviors—such as learning and memory, aggression, mating, and parenting, so it is essential to identify problems before behavioral phenotyping (see “Behavioral Screening of Genetically Modified Animals” in Chapter 9).
For mice, a general health assessment starts with a brief evaluation of body mass, core body temperature, and appearance of the pelage (fur). Neurologic reflexes should be assessed, including the righting reflex, the eye blink, and the ear and whisker twitch in response to tactile stimuli (Crawley, 1999). Any of the following symptoms should be recorded, treated if necessary, and considered when behavioral phenotyping is later conducted: self-mutilation, guarding, vocalization (with or without stimuli associated with pain), hunched posture, inactivity, lethargy, rough hair coat, no response to mild stimuli, increased heart or respiratory rate, anorexia for longer than 24 hours, weight loss greater than 20%, decrease in weight gain compared with aged-matched controls, and lesions (such as swelling, redness, and abnormal discharges). Any obvious deviations from the typical naturally occurring behaviors (ethogram) of mice should be noted. The mouse ethogram includes such behaviors as sleeping, resting, locomotion, grooming, ingestion of food and water, nest-building, exploration, foraging, and fear, anxiety, and defensive behavior (Brown et al., 2000).
After an initial health assessment, daily observation of the genetically modified animal should include an assessment of general activity levels, posture, haircoat condition, the presence of scratching or self-mutilation, and the general condition of the cage. When the cage is manipulated, as during cleaning, animals can be more closely examined for additional characteristics, such as response to handling; unexpected vocalization; ulceration; masses; abnormalities of the eyes,