Substances may also be administered in slow release implants—this requires
surgery and hence anesthesia (see below).
9.2.7Anesthesia
General anesthesia can be induced using a gaseous anesthetic or by injection.
Inhalatory anesthetics have the advantage that dose can be changed during the
procedure and, because of the “one-way” flow through system of the avian respi-
ratory system, clearance of the gas, and hence recovery, can be rapid. The disad-
vantage of gaseous anesthetics is that they require specialist delivery systems.
Isoflurane is the recommended agent. It induces anesthesia rapidly, and recovery
is also rapid. Ether should not be used and halothane is not as safe for birds as it
is for mammals. Perhaps the best agent for injection is propofol. This produces
a rapid induction of anesthesia with good muscle relaxation. Recovery is rapid
and non-traumatic. Propofol must be given be intravenous injection at a dose of
10–14 mg kg^1. However, propofol-induced anesthesia is of short duration and
this may not be appropriate for longer procedures. Ketamine has been widely
used for birds (20–50 mg kg^1 , given subcutaneously or intramuscularly). It is a
good sedative but a poor anesthetic. Muscle relaxation is poor, recovery is slow
and it is also violent—birds can injure themselves if not cared for appropriately.
Ketamine is better used in combination with other agents such as diazepam,
midazolam, or medetomidine. Post-operative analgesia is recommended. For
further details on anesthesia, analgesia, and post-operative care, see Laboratory
Animals Volume 35, Suppl. 1 (2001) “Laboratory birds: refinements in hus-
bandry and procedures,” which is also available at http://www.rsm.ac.uk/pub/la.htm,
Ritchieet al. (1994) and Altman et al. (1997).
9.2.8Implants
Many experiments involve injecting substances into birds, for example, to
induce anesthesia, to investigate the acute effects of exposure to a pollutant or
pesticide, or for studies using doubly labeled water. In other cases, long-term
treatment is necessary, for example, to investigate the role of a particular
hormone or the effects of chronic exposure to a pollutant. Repeated injections
should be avoided wherever possible—the treatment is less scientifically valid
and can cause undue stress. In theses cases, implants can be used. Two types of
implants are commonly used.
Silastic implants. Silastic tubing (manufactured by DowCorning) is permeable
to small non-polar molecules. The tubing can be cut to the desired length, one
open end is sealed with silicone adhesive, the substance of concern is packed into
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