Biomedical Engineering Reference
In-Depth Information
retention and deposition of water along the arms, shoulders,
and back (
Jack, 2007
), as well as increases in testicular
volume of 150% (
Wiebe et al., 1984
) and increases in
aggressive behavior related to increasing circulating
androgens (
Wiebe et al., 1988
). During the nonbreeding
season, male rhesus macaques display reduced LH
pulsatility (4 to 6 pulses per day (
Plant, 1980; Wickings
et al., 1986
)), reduced diurnal rhythms in pulsatility
(
Wickings et al., 1986
), regression of seminiferous tubules,
and few spermatocytes or spermatids. In the months leading
into the mating season, LH pulsatility increases, seminif-
erous tubular diameter increases threefold (
Conaway and
Sade, 1965
), and spermatogenesis commences (
Zamboni
et al., 1974; Wickings et al., 1986
). Breeding males also
display skin reddening,
the dominance status of the male is based more upon
individual factors (age, temperament, size) than on rela-
tions. In colony-reared animals, males are usually deliber-
ately culled from the group, ensuring an increase in
stability and a decrease in potential for loss of genetic
heterogeneity (
Pusey and Packer, 1986; Beisner et al.,
2010
). Maintaining stability and decreasing aggression
within groups is aided by a stable dominance hierarchy
within each sex. Within large social groups there will be
multiple matrilines, and the possibility of one matriline
being overthrown is not uncommon. This situation happens
when lower ranking matrilines group together and displace
the highest ranking matriline. A retrospective analysis at
The California National Primate Research Center revealed
that matriline overthrows were more likely to occur if the
alpha female had been removed from the group (
Oates-
O'Brien et al., 2010
). In addition, during the breeding
season there appeared to be an increased risk of overthrows
that was associated with increased levels of aggression
between animals (
Eaton et al.,1981
).
Schemes for breeding macaques are numerous and
include semi-free-ranging island populations, large
outdoor corrals with multi-male, multi-female groups,
smaller outdoor or indoor housing with single-male, multi-
female groups, and individually housed females who are
timed mated. The choice of grouping type is governed by
the practicalities of available space, climate concerns,
pathogen control concerns, and the planned use of the
offspring.
Several studies have documented and compared repro-
ductive parameters among these various breeding schemes.
The parameters most often calculated and compared are:
(1) conception or pregnancy rate
likely related to increasing
T production.
The roles of specific environmental cues in generating
these neuroendocrine changes in squirrel monkeys and
rhesus macaques remain obscure; however, changing day
length cues do not appear necessary, as these patterns are
retained in controlled day length conditions (
Wehrenberg
and Dyrenfurth, 1983
).
Reproductive function of adult males can be influenced
by both intrasexual and intersexual stimuli in a wide variety
of nonhuman primates. Typically, cues from other adult
males may dampen the activity of the HPG axis whereas
interactions with females will have stimulatory effects. See
Saltzman et al. (2011)
for a more detailed discussion of this
topic.
HOUSING, HUSBANDRY, AND
POPULATION MANAGEMENT
FOR BREEDING
Macaques
Macaques are the nonhuman primates most commonly
used in biomedical research. In 2010, the two macaque
species in highest demand and, therefore, having the largest
number of breeding programs were the rhesus macaque
(Macaca mulatta) and the cynomolgus macaque (Macaca
fascicularis). The details provided in this section regarding
macaque breeding apply generally to most macaque
species.
Macaques in the wild live in large multi-male, multi-
female groups (see Chapter 5). Most groups comprise one
male for every 2.4 females (
Southwick et al., 1965
). This
ratio of males to females appears to promote stability
within the groups. Female offspring inherit the rank of their
mother and, unlike male offspring, remain closely associ-
ated with their group and hierarchy throughout their life
(
Lutz and Novak, 2005
; see Chapter 5). In the natural
environment, males will move out of their natal group at
maturity and attempt to incorporate into a new group; thus,
number of documented
pregnancies/average number of females at risk for preg-
nancy; (2) loss rates
¼
number of pregnancies documented
but not carried to term/number of pregnancies documented;
(c) production rate
¼
number of young weaned/number of
pregnancies documented.
Table 8.4
provides reproduction rates as reported in the
literature for rhesus and cynomolgus macaques in a variety
of breeding schemes. The highest pregnancy and repro-
duction rates are generally associated with provisioned,
free-ranging populations. A notable example of such
a population is the free-ranging colonies of rhesus
macaques maintained on the island of Cayo Santiago,
Puerto Rico, from the 1940s to the present (see
Koford,
1965; Carpenter, 1972; Rawlins and Kessler, 1986
, for
history of this colony). An analysis of rhesus reproduction
from 1976 to 1983 (
Rawlins and Kessler, 1986
) reported an
average reproduction rate of 80.3%. Of the total births,
95.7% were live births. The average interbirth interval was
372 days for rhesus females who had produced a live,
weaned infant in the preceding breeding season and 336
days for those females who had not.
¼
