Agriculture Reference
In-Depth Information
Table 7.1
Ovarian activity and ovulation rate 26, 32, and 38 hours following the onset of estrus in
does during the breeding season.
Time following the onset of estrus
26 h
32 h
38 h
No. of does
15
10
15
Mean (
±
SD) body weight of does (kg)
49.5
±
12.8
47.2
±
14.6
49.2
±
14.3
Mean (
±
SD) weight (total) of ovaries (g)
4.17
±
2.0
3.82
±
1.49
3.9
±
1.47
Mean number of follicles/doe
>
0 (
±
SD)
8.15
±
3.5
9.5
±
4.1
13.1
±
5.0
Mean (
±
SD) size of follicles/group (mm)
4.2
±
2.3
4.2
±
2.0
3.7
±
1.5
Mean (
±
SD) number of ovulations/doe ovulated
1.0
±
0.0
1.0 *
1.87
±
0.92
% does ovulated/does in estrus
13.3
10.0
86.7
* one observation only
Source: Greyling, 1988 .
(Chemineau, 1983; Kassem et al., 1989; Chemineau et al.,
1992 ).
Table 7.2
Mean (
SE) reproductive traits in
Damascus does under semiarid conditions.
±
Parameter
Time of Ovulation and Ovulation Rate
The doe is a spontaneous ovulator, ovulating near the end
of estrus. Ovulation rate as such refers to the number of
eggs or ova liberated from the ovary at a given estrous
period, with the time of ovulation being very important
especially in AI programs and even with natural mating.
Ovulation in does is generally reported as occurring a few
hours after the termination of standing estrus or toward the
end of estrus (24-36 hours after the onset of estrus) so that
the processes of mating and ovulation are synchronized
(Table 7.1). For successful fertilization, the timing of these
two processes is critical. It has been shown that the
maximum number of follicles ovulating is at approxi-
mately 48 hours after the onset of estrus in Black Bengal
nanny goats. The mean ovulation rate recorded in Boer
goat does was 1.72 ± 0.9 ovulations per doe (ranging
between 1 and 4 ovulations per doe). This is higher than
the ovulation rate of 1.43 quoted for Barbari nannies, the
1.2 for Angora does, and the 1.28 in Norwegian goats,
while being substantially lower than the 4.0 quoted for
Black Bengal nanny goats. Ovulation rate is normally
refl ected by the kidding rate (prolifi cacy) and as can be
expected, there is considerable variation in the kidding
rates among the different goat breeds. Among the environ-
mental factors infl uencing ovulation rate, season and the
level of nutrition are the most important (Table 7.2).
Generally ovulation rates are higher early in the natural
breeding season than later, but factors such as body size,
body weight and condition, and genotype may also con-
tribute to an increase in ovulation rate (Greyling, 1988;
Gordon, 1997 ; Jainudeen et al., 2000 ).
Estrous cycle length (d)
19.5
±
0.58
Gestation length (d)
149.4
±
0.35
Litter size
1.74
±
0.1
Birth weight (kg)
2.16
±
0.1
First service conception (%)
64.2
Fertility (%)
70.0
Kid mortalities to weaning (%)
23.4
Source: Shalaby et al., 2000 .
The Gestation Period
The gestation period in farm animals is usually defi ned as
the period of time from conception to parturition. The
gestation period in goats is normally 149 days, varying
between 144 and 150.8 days. There are a variety of factors,
which could infl uence the gestation period. These include
season of the year, parity, age of the dam, sex, and number
of offspring at birth. The mean gestation length in the Boer
goat is set at 148.2 ± 3.7 days, consistent with other reports
on goats. Heredity plays an important role in determining
gestation length, and the genotype of the fetus accounts for
almost two-thirds of the variation in gestation length. For
example, male kids are carried longer than female kids,
spring-born kids longer than fall-born kids, and singles
longer than twins. The effect of nutrition on fetal develop-
ment during certain months of pregnancy does tend to
shorten or lengthen the gestation period, but the variation
due to this factor is only 1.5 days. If periods as short as
this are considered to represent real differences in gesta-
tion length, then the discrepancy that exists in determining
