Abstract :
Fifteen nulliparous and nine multiparous Serrana goats were used, through two successive oestrous cycles, in order to
characterize their ovulation time with regard to the number of ovulations after induced and natural oestrus during the
breeding season. The onset of oestrus was detected by the amount of vasectomized bucks after oestrus synchronization
with prostaglandin, given 10 days apart, and in the following two expected natural oestrus. The preovulatory LH peak was
determined from blood samples collected 0, 4, 8, 12, 16, 20 and 24 h after onset of oestrus. A transrectal ovarian ultrasound
scanning was performed 20, 24, 28, 32, 36, 40, 44 and 60 h after onset of oestrus, for the detection of ovulations by means of
the disappearance of large follicles (.4 to 5 mm). Single ovulations were observed in 76% of oestrous periods in nulliparous
goats and in 18% of nulliparous goats. The onset of oestrus to LH peak interval was lower in nulliparous (12.160.9 h, n538)
than in multiparous (15.661.0 h, n522, P,0.05) goats with no oestrus interaction effects (P.0.05). The LH peak to first
ovulation interval was higher after natural (18.960.7 h, n536) than after induced (15.861.2 h, n524, P,0.05) oestrus.
The onset of oestrus to total ovulation interval was influenced by parity (P,0.01) and oestrus type (P,0.05) with a length
of 30.161.1 h (n515) and 33.461.5 h (n59) for induced oestrus of nulliparous and multiparous goats, respectively, and
32.561.0 h (n523) and 36.561.1 h (n513) for natural oestrus of nulliparous and multiparous goats, respectively. The onset
of oestrus to first ovulation interval was not influenced by parity, but an interval of 8.061.6 h was observed between the
first and second ovulations in polyovulatory oestrus. Consequently, nulliparous goats that are predominantly monovular ovulate
earlier than multiparous goats that are predominantly polyovulatory. In conclusion, significant differences occurred in the
number and time of ovulations between nulliparous and multiparous goats. More research is necessary for a deeper
understanding of the mechanisms regulating monovularory and polyovulatory oestrous cycles regarding the parity of goats.
Keywords: ovulation, luteinizing hormone, oestrus, ultrasonography, goats
Introduction
The correct temporal relationship between timed artificial
insemination (TAI) and ovulation is crucial for obtaining
high fertility rates in different animal production industries
(Leboeuf et al., 2003; Menchaca et al., 2004; Roelofs et al.,
2006). This can be achieved by knowing the time from
onset of oestrus to ovulation in natural oestrus and in
hormone-induced oestrus.
In goats, several works for determining ovulation time
after natural and induced oestrus by serial laparoscopies
have been reported over the last two decades (Gonzalez-
Stagnaro et al., 1984; Baril and Vallet, 1990; Leboeuf et al.,
1996). However, the serial laparoscopic ovarian examination
is a stressful method that is gradually becoming
unacceptable (Baril et al., 2000). In order to control the
laparoscopic stress effect, the number of serial laparoscopies
in goats can be restricted (Leboeuf et al., 1996).
There is a great deal of proof that the stress can affect
reproductive parameters and consequently modify the precise
time of ovulation (Dobson et al., 2000). In contrast,
ultrasonography is a safe non-invasive technique for ovarian
scanning in goats (Baril et al., 2000; Simo˜ es et al.,
2006). In cattle, it was already demonstrated that repeated
rectal ultrasound does not alter behavioural oestrus and
peri-ovulatory hormonal profiles (Roelofs et al., 2004).
Ultrasonographic studies on ovulation in goats were
first reported by Gonzalez-Bulnes et al. (2004). The time
of ovulation was determined by ultrasonography after
oestrus synchronization in goats using oestradiol benzoate,
medroxiprogesterone acetate and/or fluorogestone acetate
- (FGA) (Valenzuela-Jime´ nez et al., 2004; Martı´nez-A´ lvarez E-mail: jsimoes@utad.pt
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