Agriculture Reference
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Table 7.6 The time of ovulation, ovulation rate, follicular activity, and mean serum progesterone
concentrations at the onset of estrus in Boer goat does, following treatment with progestagen.
Duration of progestagen treatment (days)
Item
12
14
16
18
Time of ovulation relative to onset of estrus (h)
30.8
±
2.8
29.6
±
7.2
33.6
±
10.4
29.8
±
2.4
Range (h)
26.0 - 32.8
26.0 - 42.5
26.0 - 48.5
25.5 - 32.5
Mean ovulation rate (No. of ovulations/doe ovulating)
1.4
±
0.9
1.5
±
0.6
1.4
±
0.6
1.25
±
0.5
No. follicles
>
0.2 cm at time of ovulation
5.7
±
1.4
5.1
±
2.0
4.9
±
1.7
5.8
±
1.6
Mean serum progesterone concentration at onset of
estrus (ng/ml)
0.38
±
0.14
0.39
±
0.13
0.36
±
0.06
0.37
±
0.07
Does ovulating per does showing estrus (%)
71.4
62.5
57.1
80.0
Note: Values in the body of the table are mean ± S.D.
Source: Greyling, 1988 .
(37.4 ± 8.6 h) of the doe. The serum progesterone levels
throughout the induced estrous period have been shown to
vary between 0.31 and 1.4 ng/ml, and the plasma LH
surges occurring after the administration of exogenous
progesterone have been shown to be lower than those
occurring during unsynchronized LH surges. Subnormal
circulating LH levels could be associated with lower fertil-
ity. The position of the preovulatory LH surge (indication
of ovulation) and amplitude relative to the onset of the
induced estrus was found not to be signifi cantly affected
by the synchronization of estrus. These are all aspects to
keep in mind when using controlled breeding in goats
(Table 7.6) (Corteel et al., 1988; Gordon, 1983, 1997;
Greyling and Van der Nest, 2000).
The administration or route of administration of eCG
(FSH) has no signifi cant effect on the estrous response of
goats, during the breeding season. A low dose of eCG
(375 IU), however, does result in a more predictable and
precise synchronization of estrus. Outside the natural
breeding season, the use of eCG is recommended. The
route of PMSG administration seemingly has a minor
impact on the time to estrus, although there is a tendency
for goats treated intramuscularly to have a more compact
and faster estrous response, compared to those injected
eCG subcutaneously. The duration of the induced estrous
period tends to be signifi cantly longer following the exog-
enous administration of FSH due to a possible elevated
plasma oestrogen level following follicular stimulation.
The effect of this prolonged estrous period on fertility is
unsure. eCG treatment in some cases may cause problems
in sperm transport and sperm survival and hence possible
reduced fertility (Table 7.7) (Greyling and Van Niekerk,
1990a ).
The proof of successful synchronization in goats lies in
the conception rate obtained. Factors affecting the effi -
ciency of synchronization, and hence the fertility results
obtained, include the dose of intravaginal progestagen
(perhaps the most important), time relationship between
the induced estrous and the preovulatory LH surge, body
condition of the does, season, age of the doe, and parity.
There is speculation that the amount of steroid actually
released from the intravaginal sponge and the uniformity
of the release over the treatment period is more important
than the actual dose impregnated in the sponge (Table 7.8).
Conception rates (AI 48 and 60 hours following sponge
withdrawal) of 70 and 80% have been reported in indige-
nous SA feral and Boer goats, respectively, when using
different progestagen doses. In both the smaller indigenous
(mean body weight 24.7 ± 4.8 kg) and larger (mean body
weight 54.7 ± 6.8 kg) Boer goat does, halved medroxy
acetate progesterone (MAP) sponges were as effi cient as
whole 60 mg MAP intravaginal sponges in the synchroni-
zation of estrus (Gordon, 1997; Greyling and Van der Nest,
2000 ; Motlomelo, 2000 ).
Estrus in goats can also be effi ciently synchronized
when using two injections of prostaglandin (inside the
natural breeding season) 11-14 days apart. Prostaglandin
causes luteal regression between days 5 and 16 of the
estrous cycle in the doe. CLs outside this stage of the cycle
are not always sensitive to prostaglandin, the so-called
refractory period. Synchronization with two injections of
prostaglandin outside the normal breeding season leads to
poor estrous responses and very low conception rates indi-
cating that prostaglandin is only effective in the active
breeding season and with an active corpus luteum present.
The use of a short progestagen treatment (8 days) followed
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