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Ovarian activity of Yankasa Sheep using abattoir specimens
THERIOGENOLOGY OVARIAN ACTIVITY OF YANKASA SHEEP USING ABATTOIR SPECIMENS J. 0. Hambolua S. A. Ojo, M. N. Jamdar, and E. C. I. Molokwu' Ahmadu Belle University, Zaria, Nigeria Department of Anatomy Faculty of Veterinary Medicine 1 Department of Physiology and Pharmacology Faculty of Veterinary Medicine Received for publication: January 30, 1984 Accepted: November 29, 1984 ABSTRACT Seventy-five pairs of ovaries from Yankasa Sheep aged 1% to 3 years were collected from a Zaria abattoir for 12 months, to study the ovarian activity. It was observed that ovarian activity in Yankasa sheep was year-round with maximum activity occurring during the rainy and pre-rain seasons. These periods of maximum ovarian activity might be caused by the availability of pasture during the rainy and pre-rain seasons, since Nigerian sheep obtain most of their food by grazing available pasture. Key words:
Yankasa, sheep, ovarian activity INTRODUCTION
Sheep production in Nigeria is mainly in the hands of smallholders who keep a few sheep primarily for meat and as a quick source of income (1). In Zaria, sheep are sold for slaughter throughout the year without any regard to reproductive efficiency and reasons for slaughter are not affected by season and age (1). The sale of sheep is never on a commercial basis, but a family would usually sell some animals from the flock to meet an occasional financial need, except during muslim festivals when a lot of rams are sold (2). Breeding seasons of domestic sheep vary in some breeds (3). In the tropics, ewes show oestrus throughout the year (due to an equal light and dark ratio) (4) and breeding season is not restricted (3,s). Hampshire ewes at the equator lamb year-round with peak
aCurrent address: Kansas State University, Department of Anatomy and Physiology, Manhattan, KS 66506. Acknowledgement: The authors wish to thank Ahmadu Belle University, Zaria, for funding this research.
FEBRUARY
198.5 VOL. 23 NO. 2
263
THERIOGENOLOGY
lambing activity in April and October (6). The Indian native sheep are nonseasonal in sexual activity but show concentration of lambing in certain seasons (4,5). Yankasa sheep are said to be year-round breeders, although lambing activity is greater in certain months (7). Reports on ovarian activity in Yankasa sheep are lacking. This study reports ovarian activity in Yankasa sheep using ovarian biometric parameters obtained from abattoir specimens. MATERIALS AND METHODS In Zaria environs, each year may be considered to be made up of four seasons: dry, January to March; pre-rain, April to May; rainy, June to September; and pre-dry, October to December. For one year during each season ovaries were collected Monday, Wednesday and Friday of each week between 06:OO and 08:OO hours at a Zaria abattoir. Prior to slaughter, each sheep was aged by examining the incisor teeth (8). To ensure that only sexually mature ewes were considered, only samples of open animals aged 1.5 to 3 years were used; thus, samples were not available on certain days. Seventy-five pairs of ovaries were collected during the 12 months of study. The pairs of ovaries were collected in sample bottles containing physiological saline. The length (distance between the cranial and caudal poles) and width (distance between free and attached borders) were measured in millimeters using screw-gauge calipers. The weights were measured in milligrams using a Mettler balance. Following morphometric measurements, the ovaries were placed in Bouin's fixative solution for 24 hours. Each ovary was sectioned sagittally and processed for microscopic studies using standard histotechnics. Haematoxylin and eosin (H&E) were the stains employed. The stained slides were examined under low power (x40). Ovarian follicles (Graafian, atretic Graafian, secondary and atretic secondary) corpora lutea and corpora albicantia were identified using the method of Hafez (3). The number of secondary follicles, Graafian follicles, atretic i;raafianand atretic secondary follicles, corpora lutea and corpora albicantia were counted in each section. Three slides per ovary were examined. The data was then subjected to analysis of variance (9). RESULTS The data revealed no significant differences between seasons (P > 0.05) (Table 1). Figures 1 and 2 show that length and width measurements were high during rainy season, dropped during the pre-dry season, and then increased during the pre-rain season. Figure 3 shows that weights were greater during the pre-rain and rainy seasons than during the pre-dry and dry seasons. The number of Graafian follicles fell gradually from rainy season to pre-dry season but fell sharply during the dry season; they increased again, however, during the pre-rain season (Fig. 4).
264
FEBRUARY
1985 VOL. 23 NO. 2
%! VI
Comments:
23.25
1.75
18.25
3.25
25.00
33.67
1.17
12.17
5.83
12.50
21.75
0.75
15.50
4.25
15.75
implies non-significance between seasons (P > 0.05). Standard error was used instead of standard error of difference (SED) because the unequal replications of seasons made the interpretation of comparisons difficult.
NS
17.75
3.13
No. of corpora lutea
No. of corpora albicantia
15.75
4.25
18.88
No. of atretic secondary follicles
No. of secondary follicles
No. of atretic Graafian follicles
6.12
No. of Graafian follicles 6.50
8.18
7.47
6.75
9.04
Width (mm)
5.17
10.42
9.68
8.83
11.58
Length (mm)
6.00
647.23
500.08
396.68
609.69
Weight (mg)
Pre-Rain (mean values) n = 13
Dry (mean values) n = 25
Pre-dry (mean values) n = 11
Rainy (mean values) n = 26
Effect of season on ovarian biometrical parameters in sheep
Biometrical Parameter
Table 1:
NS
1.89
16.41
1.79
10.02
3.59
15.23
4.89
NS
NS
NS
NS
NS
NS
NS
NS
166.92
1.60
Significance
SE
THERIOGENOLOGY
Fig.
1 Effect
of
season
on
ovarian
length
(Sheep1
------
Right
---8---
Laft
Ovary
---A---
Laft ond
Ovary Right Ovary
j
‘,
7-
26 _I SL3zl-
Pra-dry
RCJlny
Pro-rain
Dry
Soosons Fig.
2
Effect
of
season
on
ovarian
----*-----e----
‘I
Rainy
Pra-dry
sonson
266
DCY
width
(Sheep]
Right Ovory Loft Ovary Left and Right
Ovory
Pro-roln
5
FEBRUARY
1985 VOL. 23 NO. 2
THERIOGENOLOGY
Fig. 3
Effect
of
season
on
ovarian
weight
(Sheep)
700-
600 -
----x---
500-
_c
-o-
Right OVOrY Loft Ovary Loft and Right
Ovary
400-
t
300-
2
I ROklY
Pre-dry Sea
ig
L
Effect
FEBRUARY
of
season
on
number
Pra-roln
Dry *on
5 ot
1985 VOL. 23 NO. 2
graaflon
follicles
sheep1
267
The number of atretic Graafian and atretic secondary follicles were highest during the pre-dry season and dropped during the dry season (Figs. 5 and 6). However, the number of secondary follicles was lowest during the pre-dry season but highest during dry season (Fig. 7). The number of corpora albicantia rose during the rainy season, reached a peak during the dry season, and then dropped during the pre-rain season (Fig. 8). The number of corpora lutea reached its peak during rainy season (Fig. 9). Table 2 shows the change in rainfall from rainy to pre-dry season.
Fig. 5
Effect
of season on
number of atretlc graatlan
30-
fotllalesfihtep~
----^ -
RQhl Ovary LH ovary
-.--
Let1 ond Right Ovary
n 250 3 ._ = ,o 20z ._ ; 150 01 s b
lo-
x s =
5.
I30illy
268
Pro-dry 0rY soosons
prr-rein
FEBRUARY
1985 VOL. 23 NO. 2
THERIOGENOLOGY Fig.
6
Effect
of
season
on
number
35-
of
otretic
-- -- Rtght -Loft
;
-
30-
secondary
follicles
ISheep
Ovary Ovary
Lo,,
and
RaghI
Ovary
= ,o E IS: 2 : ul zoY ? z
15-
0 b 2 lo: 5-
R01ny
Pre-dry
OCY
P
seasons Fig.
7
FEBRUARY
Effect
of
season
on
number
1985 VOL. 23 NO. 2
of
sccondory
follicles
ISheep
---_F--
Right
-
Loft
ovary
Ovary
--
LPII
and
Rlghf
Ovary
269
THERIOGENOLOGY
m.
8
Ettect
of
season
on
number
ot
corpora
alblcont~o
Iw-~eepr
40I
3530-
---+-
Right
-
LOif
-Loft
ROII-IY
Pro-dry
Ovary Ovary and
Right
Ovary
PW-rOlCT
09
Soosonr Fig.
270
9
Effoclof
Season
on number
of corpora
luleo
--x--
Right
-
Left
-+-
RughI and Ovary
(Sheep)
Ovary ovary
FEBRUARY
1985 VOL. 23 NO. 2
THERIOGENOLOGY Table 2:
Effect of season on mean temperature, day length and rainfall
Rainy
Pre-dry
Dry
Pre-Rain
Comments
Temperature ("C)
24.48
23.03
24.47
26.75
*
Mean-day length (hr)
12.52
11.70
11.77
12.45
**
223.20
13.53
0
79.05
**
Rainfall (mm)
Comments:
*Significant P < 0.01 **Significant P < 0.001 DISCUSSION
By using the ovarian parameters, it was found that the Yankasa sheep can conceive throughout the year. The number of Graafian follicles peaked during the rainy season, gradually declined during the pre-dry and fell sharply during the dry season, but began to increase again during the pre-rain season. Also, during the rainy season, the number of corpora lutea peaked indicating the period of maximum ovarian activity. Peak ovarian activity during the rainy season corresponds to abundant pasture during the same period. This study shows that ovarian activity in Yankasa sheep peaks during the rainy season and drops during the pre-dry and dry seasons, with the activity increasing again during the pre-rain season. The results of this study agree with the work of others (7). who observed that ovarian activity was year-round in Yankasa sheep based on records from Ahmadu Belle University Farm. They also deduced that maximum ovarian activity occurred in late March or early April to July. This period corresponds to the periods of maximum ovarian activity (pre-rain and parts of rainy season) observed in this study. Some workers (5) also observed year-round oestrus in tropic sheep and they suggested that an equal light and dark ratio could be responsible. The drop in number of Graafian follicles during the pre-dry and dry seasons, the highest number of atretic Graafian and atretic secondary follicles during the pre-dry season and corpora albicantia during the dry season is perhaps due to the unfavorable climatic conditions during these seasons. The rainfall dropped sharply from 223.20 mm during the rainy season to 13.53 mm and zero during pre-dry and dry seasons respectively. Since atresia is an unfavorable condition, it is expected that the number of atretic Graafian and secondary follicles and corpora albicantia would be highest during pre-dry and dry seasons, when there is a sharp change in environmental factors.
FEBRUARY
1985 VOL. 23 NO. 2
271
THERIOGENOLOGY
The number of secondary follicles was highest during the dry season; this was expected because the number of Graafian follicles during this period was lowest. In conclusion, the maximum period of ovarian activity in Yankasa sheep corresponds to rainy and pre-rain seasons when pasture is readily available for the sheep. REFERENCES 1.
Adu, I.F. and Ngere, L.O. The indigenous sheep in Nigeria. Wld. Rev. Anim. Prod., -25: 51-62 (1979).
2.
Ademosun, A.A. The development of the livestock industry in Nigeria - Ruminants. Proc. Agric. Sot. Niger. -10: 13-20 (1973).
3.
Hafez, E.S.E. Functional histology of reproduction, In: Hafez, E. S. E., 4th ed., Reproduction in Farm Animals, Lea and Febiger, Philadelphia, 1980, pp. 63-82, 141-144.
4.
Sahni, K.L., Tiwari, S.B., and Sahani, M.S. Effect of season on the occurrence of oestrus and fertility in different breeds of sheep under semi arid conditions. Ind. Vet. J. -53: 515-522 (1976).
5.
Sahni, K.L. and Roy, A.A. Study on the sexual activity of Bikaneri sheep (Ovis aries L) and conception rate through artificial insemination. Ind. J. of Vet. Sci. and Anim. Husb. -37~327-334
(1967).
6.
Anderson, J. Reproduction in improved British breeds of sheep on a tropical plateau. Proc. 5th Inter. Congr: Anim. Prod. A. I. Toronto pp. 465-469 (1965).
7.
Molokwu, E.C.I. and Umunna, N.N. Reproductive performance of the Yankasa sheep of Nigeria. Theriogenology -14: 239-249 (1980).
a.
Sisson, S. and Grossman, J.D. The Anatomy of the Domestic Animals. 5th ed., W.B. Saunders Co., Philadelphia, 1975, pp. 866-871.
9.
Walpole, R.E. Introduction to Statistics. NY, 1974, pp. 226-229, 267-275.
272
2nd ed. MacMillan,
FEBRUARY
1985 VOL. 23 NO. 2
Yankasa, sheep, ovarian activity INTRODUCTION
Sheep production in Nigeria is mainly in the hands of smallholders who keep a few sheep primarily for meat and as a quick source of income (1). In Zaria, sheep are sold for slaughter throughout the year without any regard to reproductive efficiency and reasons for slaughter are not affected by season and age (1). The sale of sheep is never on a commercial basis, but a family would usually sell some animals from the flock to meet an occasional financial need, except during muslim festivals when a lot of rams are sold (2). Breeding seasons of domestic sheep vary in some breeds (3). In the tropics, ewes show oestrus throughout the year (due to an equal light and dark ratio) (4) and breeding season is not restricted (3,s). Hampshire ewes at the equator lamb year-round with peak
aCurrent address: Kansas State University, Department of Anatomy and Physiology, Manhattan, KS 66506. Acknowledgement: The authors wish to thank Ahmadu Belle University, Zaria, for funding this research.
FEBRUARY
198.5 VOL. 23 NO. 2
263
THERIOGENOLOGY
lambing activity in April and October (6). The Indian native sheep are nonseasonal in sexual activity but show concentration of lambing in certain seasons (4,5). Yankasa sheep are said to be year-round breeders, although lambing activity is greater in certain months (7). Reports on ovarian activity in Yankasa sheep are lacking. This study reports ovarian activity in Yankasa sheep using ovarian biometric parameters obtained from abattoir specimens. MATERIALS AND METHODS In Zaria environs, each year may be considered to be made up of four seasons: dry, January to March; pre-rain, April to May; rainy, June to September; and pre-dry, October to December. For one year during each season ovaries were collected Monday, Wednesday and Friday of each week between 06:OO and 08:OO hours at a Zaria abattoir. Prior to slaughter, each sheep was aged by examining the incisor teeth (8). To ensure that only sexually mature ewes were considered, only samples of open animals aged 1.5 to 3 years were used; thus, samples were not available on certain days. Seventy-five pairs of ovaries were collected during the 12 months of study. The pairs of ovaries were collected in sample bottles containing physiological saline. The length (distance between the cranial and caudal poles) and width (distance between free and attached borders) were measured in millimeters using screw-gauge calipers. The weights were measured in milligrams using a Mettler balance. Following morphometric measurements, the ovaries were placed in Bouin's fixative solution for 24 hours. Each ovary was sectioned sagittally and processed for microscopic studies using standard histotechnics. Haematoxylin and eosin (H&E) were the stains employed. The stained slides were examined under low power (x40). Ovarian follicles (Graafian, atretic Graafian, secondary and atretic secondary) corpora lutea and corpora albicantia were identified using the method of Hafez (3). The number of secondary follicles, Graafian follicles, atretic i;raafianand atretic secondary follicles, corpora lutea and corpora albicantia were counted in each section. Three slides per ovary were examined. The data was then subjected to analysis of variance (9). RESULTS The data revealed no significant differences between seasons (P > 0.05) (Table 1). Figures 1 and 2 show that length and width measurements were high during rainy season, dropped during the pre-dry season, and then increased during the pre-rain season. Figure 3 shows that weights were greater during the pre-rain and rainy seasons than during the pre-dry and dry seasons. The number of Graafian follicles fell gradually from rainy season to pre-dry season but fell sharply during the dry season; they increased again, however, during the pre-rain season (Fig. 4).
264
FEBRUARY
1985 VOL. 23 NO. 2
%! VI
Comments:
23.25
1.75
18.25
3.25
25.00
33.67
1.17
12.17
5.83
12.50
21.75
0.75
15.50
4.25
15.75
implies non-significance between seasons (P > 0.05). Standard error was used instead of standard error of difference (SED) because the unequal replications of seasons made the interpretation of comparisons difficult.
NS
17.75
3.13
No. of corpora lutea
No. of corpora albicantia
15.75
4.25
18.88
No. of atretic secondary follicles
No. of secondary follicles
No. of atretic Graafian follicles
6.12
No. of Graafian follicles 6.50
8.18
7.47
6.75
9.04
Width (mm)
5.17
10.42
9.68
8.83
11.58
Length (mm)
6.00
647.23
500.08
396.68
609.69
Weight (mg)
Pre-Rain (mean values) n = 13
Dry (mean values) n = 25
Pre-dry (mean values) n = 11
Rainy (mean values) n = 26
Effect of season on ovarian biometrical parameters in sheep
Biometrical Parameter
Table 1:
NS
1.89
16.41
1.79
10.02
3.59
15.23
4.89
NS
NS
NS
NS
NS
NS
NS
NS
166.92
1.60
Significance
SE
THERIOGENOLOGY
Fig.
1 Effect
of
season
on
ovarian
length
(Sheep1
------
Right
---8---
Laft
Ovary
---A---
Laft ond
Ovary Right Ovary
j
‘,
7-
26 _I SL3zl-
Pra-dry
RCJlny
Pro-rain
Dry
Soosons Fig.
2
Effect
of
season
on
ovarian
----*-----e----
‘I
Rainy
Pra-dry
sonson
266
DCY
width
(Sheep]
Right Ovory Loft Ovary Left and Right
Ovory
Pro-roln
5
FEBRUARY
1985 VOL. 23 NO. 2
THERIOGENOLOGY
Fig. 3
Effect
of
season
on
ovarian
weight
(Sheep)
700-
600 -
----x---
500-
_c
-o-
Right OVOrY Loft Ovary Loft and Right
Ovary
400-
t
300-
2
I ROklY
Pre-dry Sea
ig
L
Effect
FEBRUARY
of
season
on
number
Pra-roln
Dry *on
5 ot
1985 VOL. 23 NO. 2
graaflon
follicles
sheep1
267
The number of atretic Graafian and atretic secondary follicles were highest during the pre-dry season and dropped during the dry season (Figs. 5 and 6). However, the number of secondary follicles was lowest during the pre-dry season but highest during dry season (Fig. 7). The number of corpora albicantia rose during the rainy season, reached a peak during the dry season, and then dropped during the pre-rain season (Fig. 8). The number of corpora lutea reached its peak during rainy season (Fig. 9). Table 2 shows the change in rainfall from rainy to pre-dry season.
Fig. 5
Effect
of season on
number of atretlc graatlan
30-
fotllalesfihtep~
----^ -
RQhl Ovary LH ovary
-.--
Let1 ond Right Ovary
n 250 3 ._ = ,o 20z ._ ; 150 01 s b
lo-
x s =
5.
I30illy
268
Pro-dry 0rY soosons
prr-rein
FEBRUARY
1985 VOL. 23 NO. 2
THERIOGENOLOGY Fig.
6
Effect
of
season
on
number
35-
of
otretic
-- -- Rtght -Loft
;
-
30-
secondary
follicles
ISheep
Ovary Ovary
Lo,,
and
RaghI
Ovary
= ,o E IS: 2 : ul zoY ? z
15-
0 b 2 lo: 5-
R01ny
Pre-dry
OCY
P
seasons Fig.
7
FEBRUARY
Effect
of
season
on
number
1985 VOL. 23 NO. 2
of
sccondory
follicles
ISheep
---_F--
Right
-
Loft
ovary
Ovary
--
LPII
and
Rlghf
Ovary
269
THERIOGENOLOGY
m.
8
Ettect
of
season
on
number
ot
corpora
alblcont~o
Iw-~eepr
40I
3530-
---+-
Right
-
LOif
-Loft
ROII-IY
Pro-dry
Ovary Ovary and
Right
Ovary
PW-rOlCT
09
Soosonr Fig.
270
9
Effoclof
Season
on number
of corpora
luleo
--x--
Right
-
Left
-+-
RughI and Ovary
(Sheep)
Ovary ovary
FEBRUARY
1985 VOL. 23 NO. 2
THERIOGENOLOGY Table 2:
Effect of season on mean temperature, day length and rainfall
Rainy
Pre-dry
Dry
Pre-Rain
Comments
Temperature ("C)
24.48
23.03
24.47
26.75
*
Mean-day length (hr)
12.52
11.70
11.77
12.45
**
223.20
13.53
0
79.05
**
Rainfall (mm)
Comments:
*Significant P < 0.01 **Significant P < 0.001 DISCUSSION
By using the ovarian parameters, it was found that the Yankasa sheep can conceive throughout the year. The number of Graafian follicles peaked during the rainy season, gradually declined during the pre-dry and fell sharply during the dry season, but began to increase again during the pre-rain season. Also, during the rainy season, the number of corpora lutea peaked indicating the period of maximum ovarian activity. Peak ovarian activity during the rainy season corresponds to abundant pasture during the same period. This study shows that ovarian activity in Yankasa sheep peaks during the rainy season and drops during the pre-dry and dry seasons, with the activity increasing again during the pre-rain season. The results of this study agree with the work of others (7). who observed that ovarian activity was year-round in Yankasa sheep based on records from Ahmadu Belle University Farm. They also deduced that maximum ovarian activity occurred in late March or early April to July. This period corresponds to the periods of maximum ovarian activity (pre-rain and parts of rainy season) observed in this study. Some workers (5) also observed year-round oestrus in tropic sheep and they suggested that an equal light and dark ratio could be responsible. The drop in number of Graafian follicles during the pre-dry and dry seasons, the highest number of atretic Graafian and atretic secondary follicles during the pre-dry season and corpora albicantia during the dry season is perhaps due to the unfavorable climatic conditions during these seasons. The rainfall dropped sharply from 223.20 mm during the rainy season to 13.53 mm and zero during pre-dry and dry seasons respectively. Since atresia is an unfavorable condition, it is expected that the number of atretic Graafian and secondary follicles and corpora albicantia would be highest during pre-dry and dry seasons, when there is a sharp change in environmental factors.
FEBRUARY
1985 VOL. 23 NO. 2
271
THERIOGENOLOGY
The number of secondary follicles was highest during the dry season; this was expected because the number of Graafian follicles during this period was lowest. In conclusion, the maximum period of ovarian activity in Yankasa sheep corresponds to rainy and pre-rain seasons when pasture is readily available for the sheep. REFERENCES 1.
Adu, I.F. and Ngere, L.O. The indigenous sheep in Nigeria. Wld. Rev. Anim. Prod., -25: 51-62 (1979).
2.
Ademosun, A.A. The development of the livestock industry in Nigeria - Ruminants. Proc. Agric. Sot. Niger. -10: 13-20 (1973).
3.
Hafez, E.S.E. Functional histology of reproduction, In: Hafez, E. S. E., 4th ed., Reproduction in Farm Animals, Lea and Febiger, Philadelphia, 1980, pp. 63-82, 141-144.
4.
Sahni, K.L., Tiwari, S.B., and Sahani, M.S. Effect of season on the occurrence of oestrus and fertility in different breeds of sheep under semi arid conditions. Ind. Vet. J. -53: 515-522 (1976).
5.
Sahni, K.L. and Roy, A.A. Study on the sexual activity of Bikaneri sheep (Ovis aries L) and conception rate through artificial insemination. Ind. J. of Vet. Sci. and Anim. Husb. -37~327-334
(1967).
6.
Anderson, J. Reproduction in improved British breeds of sheep on a tropical plateau. Proc. 5th Inter. Congr: Anim. Prod. A. I. Toronto pp. 465-469 (1965).
7.
Molokwu, E.C.I. and Umunna, N.N. Reproductive performance of the Yankasa sheep of Nigeria. Theriogenology -14: 239-249 (1980).
a.
Sisson, S. and Grossman, J.D. The Anatomy of the Domestic Animals. 5th ed., W.B. Saunders Co., Philadelphia, 1975, pp. 866-871.
9.
Walpole, R.E. Introduction to Statistics. NY, 1974, pp. 226-229, 267-275.
272
2nd ed. MacMillan,
FEBRUARY
1985 VOL. 23 NO. 2