Agriculture Reference
In-Depth Information
APPLIED REPRODUCTIVE TECHNOLOGIES
program (for pregnant animals with multiple fetuses),
while also preventing the slaughter of pregnant animals
and facilitating the management program. The main pre-
requisites in using the technique of pregnancy diagnosis in
goats are that it must be accurate, relatively inexpensive,
repeatable, and practical (Wildeus, 1999).
Introduction
The active interest in the control of ovulation, AI, and
embryo transfer in farm animals, and in this case, the goat,
revolves around the improvement of reproduction effi -
ciency, genetic improvement, and the output potential of
these animals. Thus, for the last 4 decades, researchers have
examined the possibility of employing hormones and dif-
ferent techniques in the control of estrus and the improved
reproductive performance in farm animals. Controlled
breeding in goats may imply breeding the animals after the
end of the normal anestrous period. It may mean breeding
females to permit a compact kidding season. It may mean
breeding does with top quality bucks by AI. It may also
mean a rapid buildup of a superior fl ock by embryo transfer
or the early diagnosis of pregnancy to increase reproduc-
tion effi ciency. Reproduction effi ciency as such is one of
the main factors that determines the overall productivity
of an animal. It also determines the rate of expansion of
the fl ock (for selection purposes), the number of excess
stock for sale, and the eventual availability of meat and
milk for human consumption (Holtz, 2005).
The manipulation of the estrous cycle in the doe involves
two alternative approaches, either (1) removing or reduc-
ing the effect of the corpus luteum (CL) on the estrous
cycle or (2) suppressing follicular development by an arti-
fi cially extended luteal phase. Suppression of follicular
development can be achieved by the use of progesterone
or its analogues, while luteolysis of the CL can be achieved
by implementing prostaglandin F
2α
Synchronization of Estrus in Does
Seasonality in the reproduction activity limits the repro-
ductive rate of the doe, and manipulation of reproduction
could increase the frequency of breeding per year and the
litter size in the specie. The effective synchronization of
estrus and control of ovulation by means of intravaginal
progestagen and/or injections of prostaglandin has been
employed in goats. This modifi cation of the ovarian cycle
has been based on the hypothesis that maximum fertility
potential depends on a fi nely balanced endocrine relation-
ship (Greyling and Van Niekerk, 1986, 1990b; Greyling
and Van der Nest, 2000).
Although sheep have shorter estrous cycles (16-17
days) than goats (21 days), an increase in the treatment
period of intravaginal progestagen sponges from 12 to 18
days has no signifi cant effect on the estrous response,
follicular activity, and ovulation rate. Fertility levels fol-
lowing intravaginal progestagen sponges (fl uorogestone
acetate [FGA]) in goats favor a longer rather than a shorter
treatment period (16 days and longer). The shorter treat-
ment with progestagen generally leads to a delayed induc-
tion of the onset of estrus. However, when using a
prostaglandin F
2α
. If the time of estrus or
ovulation is controlled, it would obviate the need for fre-
quent detection of estrus and permit fi xed - time artifi cial
insemination and a compact kidding season (Robinson,
1976 ; Boshoff, 1980 ).
One of the most exciting developments in controlled
breeding of farm animals is the use of embryo transfer.
Superovulation of does and the subsequent recovery and
transfer of embryos to appropriately synchronized recipi-
ents has been proven to be an effective means of increasing
the contribution of outstanding females to the gene pool of
a specifi c specie and decreasing the generation interval.
This technique is now used in practice commercially, with
millions of embryos being transported worldwide. The
number of superior offspring that a doe can produce can
also be greatly increased by this technique (Van der Nest,
1997; Greyling et al., 2002; Holtz, 2005).
Early pregnancy diagnosis (PD) in goats is a manage-
ment tool that has the distinct advantages of identifying
infertile animals and can be used to adjust a fodder fl ow
treatment at this intravaginal progesta-
gen treatment withdrawal, complete luteolysis can be
achieved with acceptable synchronization effi ciency.
Furthermore, administration of pregnant mare serum
gonadotrophin (PMSG) or equine chorionic gonadotrophin
(eCG) at intravaginal sponge withdrawal is necessary to
enhance fertility following AI at a fi xed time, by inducing
a more compact synchronization of estrus. Ovulation in the
goat following synchronization generally occurs between
27 and 31 hours following the onset of estrus, or 6.5 hours
prior to the end of the estrous period. The ovulation rate
per doe following synchronization quoted in the literature
varies between 4.0 in the Black Bengal nanny goat, 1.72
in the Boer goat, 1.2 in the Angora, and 1.4 in Barbari
goats. The mean interval from intravaginal sponge with-
drawal to the onset of estrus in Boer goat does is 58.4
±
22.7
hours, compared to 62.6
19.1 hours for Boer goats syn-
chronized with prostaglandin. The mean duration of the
induced estrous period (30.6
±
6.8 hours) was also found
to be shorter than that of the natural estrous period
±
