104 • Alternatives to Animal Use in Research, Testing, and Education 
consists of those studies in which pain is but a 
byproduct of the procedures used (28). 
When indices of pain are observed or antici- 
pated in living research animals as byproducts of 
an experimental protocol; the investigator is both 
informally and formally obliged to supply pain re- 
lief. (For a further discussion of the investigator’s 
responsibilities in this area, see chs. 4, 13, 14, 15, 
and 16.) 
Pain relief for a laboratory animal is usually ac- 
complished by one of three means. An analge- 
sic is an agent that relieves pain without caus- 
ing loss of consciousness. The most frequent use 
of analgesic drugs in laboratory animals is likely 
to be in the postoperative period. An anesthetic 
is an agent that causes loss of the sensation of 
pain, usually without loss of consciousness. An 
anesthetic may be classified as topical, local, or 
general, according to the breadth of its effect. 
Topical anesthetics find only limited use in ani- 
mal research, usually as components of ointments 
applied to minor injuries, whereas local anes- 
thetics are used for many minor surgical proce- 
dures. The use of local anesthetics requires post- 
surgical care, because anesthetized surfaces are 
particularly liable to accidental and self-inflicted 
damage (43). General anesthetic, either injected 
or inhaled, is widely used in research. A tran- 
quilizer is an agent that quiets, calms, and re- 
duces anxiety and tension with some alteration 
of the level of consciousness and without effect- 
ing analgesia. Tranquilizers are particularly use- 
ful in reducing distress and resistance to con- 
finement. 
The perception of pain is largely subjective. It 
is best described as an awareness of discomfort 
resulting from injury, disease, or emotional dis- 
tress and evidenced by biological or behavioral 
changes. A frequent companion to pain is dis- 
tress— the undesirable stress resulting from pain, 
anxiety, or fear (51). Distress can also occur in 
the absence of pain. An animal struggling in a re- 
straint device may be free from any pain, but it 
may be in distress. 
Despite the difficulty associated with objectively 
defining pain, it can usually be recognized. The 
most obvious sign is an animal’s behavior (16,42, 
56). Signs of pain include the following: 
• Impaired activity. Animals may be rela- 
tively inactive or may remain completely im- 
mobile within their pen or cage. If they do 
move, it is often with an abnormal gait, such 
as limping or not using a leg. 
• Change in personality. Pain may result in 
guarding behavior (attempting to protect or 
move away). Animals may also be uncharac- 
teristically aggressive. 
• Restlessness. Animals may move about 
continually or may rise up and lie down 
repeatedly. 
• Decreased intake. Food and water con- 
sumption are usually severely retarded, often 
to the extent that moderate or severe de- 
hydration can occur. 
• Abnormal vocalization. Dogs may whine or 
whimper, rats and hamsters may squeak at 
a high pitch, and primates may scream or 
grunt. 
• Abnormal posture. Dogs, cats, and rodents 
may tense the muscles of the back and ab- 
domen to effect a “tucked-up” appearance. 
• Self-mutilation. Dogs and rodents may 
gnaw at the site of a lesion on their own flesh 
or, for example, remove their own tumor. 
In identifying pain, all these criteria must be 
considered in conjunction with the nature of the 
experimental procedure and the previous normal 
behavioral characteristics of the animal. Also, it 
should be noted that no one criterion is a wholly 
reliable indicator of pain. 
An experimental procedure probably involves 
pain if it includes, for example, induction of any 
pathological state, administration of toxic sub- 
stances, long-term physical restraint, aversive 
training, or major operative procedures such as 
surgery and induction of physical trauma. Vari- 
ous procedures employed in the research labora- 
tory can be compared, ranking each for the esti- 
mated degree of pain for the animal subject (see 
table 5-3). Educated estimates of pain perception 
in animals can be made by understanding animal 
behavior; by drawing analogies based on compar- 
