Euthanasia of Rodent Fetuses and Neonates
The
Report of the AVMA Panel on Euthanasia does not provide specific recommendations
for the euthanasia of prenatal or neonatal animals. The following
guidelines are suggested to assist individual Animal Care and Use
Committees at the NIH in reviewing proposals which involve the use
of rodent fetuses or neonates.
Fetuses:
• Fetuses up to 14 days in gestation: Neural
development at this stage is minimal and pain perception
is considered unlikely. Euthanasia of the mother or
removal of the fetus should ensure rapid death of the
fetus due to loss of blood supply and non-viability
of fetuses at this stage of development.
• Fetuses 15 days in gestation to birth: The
literature on the development of pain pathways suggests
the possibility of pain perception at this time. Whereas
fetuses at this age are not sensitive to inhalant anesthetics,
euthanasia may be induced by the skillful injection
of chemical anesthetics. Decapitation with surgical
scissors, cervical dislocation, or rapid freezing (immersion
in liquid nitrogen) are acceptable physical methods
of euthanasia. When chemical fixation of the whole
fetus is required, fetuses should be anesthetized prior
to immersion in or perfusion with fixative solutions.
Anesthesia may be induced by hypothermia of the fetus,
by injection of the fetus with a chemical anesthetic,
or by deep anesthesia of the mother with a chemical
agent that crosses the placenta, e.g., pentobarbital.
The institute veterinarian should be consulted for
considerations of fetal sensitivity to specific anesthetic
agents. When fetuses are not required for study, the
method chosen for euthanasia of a pregnant mother must
ensure rapid death of the fetus.
Neonates:
• Up to 14 days of age: Acceptable methods for
the euthanasia of neonatal mice and rats include: injection
of chemical anesthetics (e.g., pentobarbital), decapitation,
or cervical dislocation. Additionally, inhalant anesthetics
(e.g., methoxyflurane used with appropriate safety
considerations), may be used. However, neonates have
a high tolerance for hypoxia, so exposure must be prolonged
(>20 minutes) and death confirmed. Immersion in
liquid nitrogen may be used only for newborns; pups
older than one day should be anesthetized prior to
freezing with liquid nitrogen. Similarly, anesthesia
should precede immersion or perfusion with chemical
fixatives. Anesthesia may be induced by inhalant or
injectable anesthetics; the institute veterinarian
should be consulted for appropriate agents and dosages.
Alternatively, when adequately justified, hypothermia
(l) may be used to induce anesthesia in pups younger
than six days.
• Older than 14 days: Follow guidelines for adults.
In all cases, the person performing the euthanasia
must be fully trained in the appropriate procedures.
References:
Phifer CB, Terry LM. 1986. Use of
hypothermia for general anesthesia in preweanling rodents. Physiol & Behav
38:887-890.
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