Agriculture Reference
In-Depth Information
Table 7.3
The effect of season on semen production and motility for the different collection
techniques in Boer and Angora goat bucks.
Electrical stimulation
Artifi cial vagina
Boer goat
Boer goat
Angora goat
Mean
monthly
Temp. ° C
Semen
volume (ml)
Motility
(1 - 5)
Semen
volume (ml)
Motility
(1 - 5)
Semen
volume (ml)
Motility
(1 - 5)
Month
Jan
20.8
1.54
±
0.78
2.77
±
0.93
3.56
±
2.32
2.29
±
0.99
1.86
±
0.64
3.19
±
1.19
Feb
19.0
1.52 ± ± 0.73
3.73 ± 0.52
2.89 ± 2.28
2.13 ± 1.36
1.68 ± 1.37
3.63 ± 0.88
Mar
17.4
1.31 ± 0.46
3.46 ± 0.78
1.78 ± 0.30
2.80 ± 1.01
1.33 ± 0.43
3.20 ± 0.71
Apr
16.6
1.73 ± 0.75
3.42 ± 0.51
1.89 ± 0.97
2.36 ± 0.75
1.54 ± 0.78
3.13 ± 0.95
May
12.4
1.50 ± 0.68
3.65 ± 0.34
1.62 ± 1.05
2.17 ± 0.82
1.83 ± 0.85
3.38 ± 0.48
Jun
9.4
1.53 ± 0.54
2.83 ± 0.88
1.46 ± 0.59
1.65 ± 0.71
1.46 ± 0.46
3.00 ± 0.78
Jul
10.4
2.03 ± 1.21
1.96 ± 0.72
2.78 ± 1.60
1.75 ± 0.85
1.87 ± 1.00
2.94 ± 0.78
Aug
18.7
1.60 ± 0.30
2.69 ± 0.46
1.50 ± 0.67
1.75 ± 1.08
1.75 ± 0.79
2.42 ± 1.66
Sept
15.3
1.20
±
0.30
2.75
±
1.06
2.40
±
1.02
2.31
±
0.37
1.40
±
0.82
2.06
±
1.24
Oct
19.3
1.56
±
0.84
2.04
±
0.99
3.05
±
1.17
1.50
±
0.89
1.25
±
0.54
3.69
±
0.46
Nov
18.3
1.52
±
0.57
3.38
±
0.83
3.05
±
1.35
2.00
±
0.93
1.88
±
1.06
3.13
±
1.30
Dec
19.9
1.73
±
0.51
3.14
±
0.82
3.82
±
2.01
2.05
±
0.98
1.69
±
0.54
3.45
±
0.86
Mean
16.46
1.56
2.99
2.48
2.06
1.63
3.10
Source: Greyling and Grobbelaar, 1983 .
the onset of gestation becomes important (Table 7.3).
Nutritional management is important during gestation for
the maintenance of the nutritional status of the dam (with
body condition score being an indicator) and also for
meeting the needs of the developing fetus(es). It is known
that approximately 70% of fetal growth occurs during the
last trimester of pregnancy (Greyling, 1988; Jainudeen
et al., 2000 ).
In the goat, it would seem as if there is a slight time lapse
prior to stimulation of the corpus luteum to maintain preg-
nancy. A response of major biological signifi cance to the
presence of a developing embryo in the uterus is the pro-
longation of the lifespan of the corpus luteum with a con-
tinuing secretion of progesterone. This is referred to (and
somewhat misleading) as the conversion of the corpus
luteum of the estrous cycle into one of pregnancy, but no
dramatic form of conversion occurs. The physiological
events are more concerned with the prevention of regres-
sion of the corpus luteum, although the synthesis of pro-
gesterone by the luteal structures may increase after this
critical stage is passed because of the luteotrophic infl uence
of the embryo and its membranes and also trophic hormone
secretion by the anterior pituitary gland. It is a known fact
that in the goat, the corpus luteum is essential for the main-
tenance of pregnancy throughout gestation, contrary to the
ewe where the corpus luteum is essential only during the
fi rst 3 months of pregnancy. It does seem as if the caprine
placental production of progesterone is small, and it would
be unlikely to infl uence the level of this hormone in the
maternal circulation. In does bearing twins, a substantial
rise in the serum progesterone is noted during the last
weeks of pregnancy, which could suggest the caprine pla-
centa produces small but detectable amounts of progester-
one. Insuffi cient evidence of any dramatic increase in
serum progesterone concentration above the levels attained
during the luteal phase of the estrous cycle suggests the
corpus luteum as being the main source of progesterone
(Hunter, 1980). A positive relationship between multiple
pregnancies and maternal serum progesterone levels has
not been observed. Serum LH data demonstrate that lutein-
izing hormone (LH) levels in the Boer goat during preg-
nancy are not static but fl uctuate apparently at random,
relatively low levels. This is consistent with evidence that
the physiological levels of progesterone (which is high
during gestation) decrease the frequency of the LH peaks.
The mean serum LH concentration was found to be
1.3 ± 0.6 ng/ml during the luteal phase of the estrous cycle,
compared to 0.4 ± 1.2 ng/ml throughout pregnancy in the
goat. Among Boer goats under extensive production
systems in South Africa, a kidding percentage of 180% is
