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Ovarian development in Meishan pigs
THERIOGENOLOGY OVARIAN
DEVELOPMENT
IN
MEISBAN
PIGS
T. Miyano, J. Akamatsu,S. Kato, I. Nanjo and S. Kanda Departmentof Animal Reproduction,Faculty of Agriculture Kobe University,Kobe 657, Japan Receivedfor publication:September 8, 1989 Accepted:February 8, 1990 ABSTRACT Ovaries collected from a total of 35 Meishan gilts of various ages were morphologically and histologicallyexamined. Vesicular follicles were first observed in ovarian sections at 45 d of age. Simultaneously, protruding follicles appeared on the surface of the ovaries, and then ovarian weight increasedrapidlywith an increasingnumber of protrudingfollicles.About half of the gilts between 75 and 90 d of age had ovaries with corpora lutea, indicatingthat some of them had started estrous cycles before reaching75 d of age. In Meishan gilts treated with exogenous gonadotropins, ovaries were stimulatedas early as 45 d of age. These results suggest that the precocityof Meishan gilts may include the developmentof vesicularfolliclesin the ovaries at an early age. Key words: Meishan pig, ovary, follicle,puberty,gonadotropin INTRODUCTION China has the longest history of domesticationof pigs (1). Many types of pigs have developed, acclimating to the various regions, and at the present, more than 100 characteristic breeds are kept in the country (2). The Taihu, distributedin the ChangjiangRiver Basin, is known as a precociousand prolific breed. There are several subbreedsof the Taihu, such as the Meishan, Erhualian. Fengjing,Jiaxing and Shatou.Meishan gilts reach puberty at about 3 mo of age, whereas gilts of Europeanor Americanbreeds reach puberty at around 7 mo of age (3-5). Moreover,the average litter size for the Meishan is sixteen,whereas it is only approximatelyten for Europeanand American breeds (5-8). Puberty in female pigs has been considered to be related closely to prepubertal ovarian development. Morphological study of the ovaries of Yorkshiregilts demonstratesthat ovarianweight increasesgraduallyfrom birth to 70 d of age, then rapidly until 112 d of age with the development of vesicular follicles,after which it remains constantuntil puberty (9). Oxender et al. (10) reported from the histologicalexaminationof the ovaries of Dutch Landrace crossbred gilts that secondary follicles appeared near the time of birth and that only a few tertiary follicleswere present in the ovary at 62 to 90 d after birth. They also reported that ovarian response to exogenous gonadotropinsappeared at 9 wk of age, when tertiary folliclesappeared in the ovaries.
Acknowledgments: We thank Daiei, Inc., for supplyingthe Meishan pigs used in this study and for their financialsupport.
APRIL 1990 VOL. 33 NO. 4
769
THERIOGENOLOGY Since Meishan gilts reach puberty at an early age, their ovarian developmentmay be different from that of other breeds. The objectivesof this study were to characterize the morphological and histologicaldevelopment of ovaries and to examine the ovarian response to exogenous gonadotropins in prepubertalMeishan gilts. MATERIALSANDMETHODS A total of 35 female offspring from Meishan pigs imported to the experimentalfarm of Kobe Universityfrom the People'sRepublicof China in 1987 were used in our study. The pigs were housed under natural conditions of day length and temperatureand were weaned at 35 d of age. They were given a ration of syntheticmilk (NihonNosan Kogyo Co., Yokohama,Japan) between 7 and 80 d of age, followedby concentratefor meat productiontesting (Nihon Nosan Kogyo Co., Yokohama, Japan). Gilt ovaries were collected after the recording of body weights at 1, 30, 45, 50, 60, 75 and 90 d of age. The weights and shapes of ovaries,numbers and diametersof folliclesand of corpora lutea observedon the surface were recorded for all gilts. Immediatelyafter that, the ovaries were fixed in Bouin's fluid, embedded in paraffin wax, serially sectioned at 5Drn thickness,and stained with hematoxylinand eosin or periodicacid-Schiff(PAS) reagent. Follicular development was examined on the ovarian sections from prepubertalgilts, and follicleswere divided into the followingclasses based on the classificationby Mossman and Duke (11) : a) primordialfollicleswith a single layer of flattened pregranulosa cells, b) primary follicles with a single layer of cuboidal granulosa cells, c) secondary follicles with stratified layers of cuboidal granulosa cells, d) follicles with one or more PAS-positive Call-Exner bodies and multilayered granulosa cells, and e) vesicular follicleswith an antrum. The percentage of each class of follicles was calculated on the basis of all follicles observed on two ovarian sections having a medulla for each ovary. For the gonadotropintreatmentexperiment,a total of 26 Meishan gilts at 30, 45, 60 or 75 d of age were used. Gilts were administrated pregnant mare serum gonadotropin (PMSG; Teikoku Zoki, Tokyo, Japan) intramuscularly,at a dose of 100 to 1000 IU per gilt, followed by intramuscularadministrationof 500 IU human chorionicgonadotropin(hCG; Sankyo Zoki, Tokyo, Japan) 72 h after PMSG treatment. Then, 41 to 47 h after hCG administration, gilts were laparotomizedand the numbers of ovulationsand of follicleslarger than 7 mm in diameter were recorded for each ovary. Ovaries recovered from 26 untreated Meishan gilts at 30, 45, 60 or 75 d of age were also examined. Data for body weight, ovarian weight, and the number of follicles and corpora lutea were representedas the mean _+ standard deviation. Statistical analysiswas performedusing Student'st-test. RESULTS MorphologicalDevelopmentof Ovaries Table 1 shows the morphologicaldevelopmentof ovaries in Meishan gilts. There was no change in ovarian weight up to 30 d of age, but it increased rapidly after 45 d of age. Since various stages of ovaries were observed, they
770
APRIL 1990 VOL. 33 NO. 4
THERIOGENOLOGY were classifiedas follows: Type 1, no follicleson the surface; Type 2, fewer than five protruding follicles (larger than 2 mm in diameter);Type 3, five or more protruding follicles and a grape-like cluster appearance; and Type 4, having corpora lutea (Figure1). As shown in Table 1, all ovaries at 1 and 30 d of age were Type 1. From 45 to 60 d of age, ovaries with protruding follicles were observed.At 75 d of age, half of the gilts had ovarieswith corpora lutea, but one gilt still had a Type-l ovary. Ovaries at 90 d of age were either Type 3 or 4, and the average number of protrudingfollicleswere 33.6 + 13.6. The number of ovulated ova, that could be distinguishedfrom the number of corpora lutea at 75 and 90 d of age, was 11.5 & 1.5 and 12.0 k 1.0 per gilt that had ovulated,respectively. FollicularDevelopmentin Ovaries In the ovarian sectionsat 1 d of age, 32% of germ cells formed egg nests. As shown in Table 2, most of the folliclesobservedat this age were primordial, but a few primary follicles were present in each section. All of the oocytes surroundedby follicularcells reached the diplotene stage in meiosis. By 30 d of age, almost all of the germ cells had formed follicles,includingprimordial,
development of ovariesin Meishangilts Tab!0I..Morphological
Ase
No.of gilts
Bodv weight
(days) examined
;
Ovarian weight
hd
Cd
Xofovaries showingTypea 12
3
4
11 4
1.1+0.3c 6.4f1Jd O.O4+-O.Old 0.04t-o.o1c*d 100
0
0
0
45 50 60
4 4 5
10.5k2.5e 0.17+0.22C*e 75 16.2k2.1' l.oS+_0.51f 13 23.6k3.21 0.52+0.49e :;
0 13 :
25 74 :
0 0 0
E
4 5
36.7+4.7l 28.9+2.lh 4.26k3.268 2.31-t_2.12f*g0
0
60
49 40
Average no.b Follicles :
Corpora lutea
d c,d
2.5f 4.3c*e 14.6+ 9.3f,g 6 4-+ 7.7e*f
0 oc
c,d
0 0 0
;*; c:d
30:8+27.4grh2.9f3.0e 33.6+13.6h 2.4+3.6d*e
a Type 1, ovarywith no follicleon the surface; Type 2, ovarywith lessthan five protruding follicles; Type 3, ovarywith fiveor more protruding follicles; Type 4, ovarywith corporalutea.See alsoFigure1. b Eachvaluerepresents the mean -t S.D.per ovary. c-lValueswith different superscripts in the samscohnnnare significantly different (P
Age (days)
follicles % of No. of with Call-Exner follicles Vesicular shapea examined Prmmxdial Primary Secondary body
Ovarian
1 xl 45-60 90
Type1 zz;
11,082 18,684
99.2 94.7
0.8 3.1
2.0
0.2
5,237 2,741 4,121 889
89.4 81.5 85.5 81.7
3.1 4.7 2.1 1.7
E 317 1.6
2.8 4.7 5.8 7.4
::: 2.7 7.6
a See footnote"a" in Table1.
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771
THERIOGENOLOGY
Figure 1. Various categoriesof ovariandevelopmentin Meishan gilts: a) Type 1, 30 days of age, with no protrudingfollicleson the surface;b) Type 2, 60 days of age, showingonly one large vesicularfollicle; c) Type 3, 60 days of age with five or more protrudingfollicleson the surface;and d) Type 4, 75 days of age with corpora lutea.
772
APRIL 1990 VOL. 33 NO. 4
THERIOGENOLOGY primary and secondaryfolliclesand follicleswith Call-Rxnerbodies. There was no egg nest in the ovarian sections.Vesicularfollicleswere first observed in the ovaries at 45 d of age. Follicular development was summarized in each category of ovary from 45 d to 60 d of age. The percentagesof follicleswith Call-Rxnerbodies and vesicular folliclesincreasedas the shape of the ovaries proceeded from Type 1 to Type 3. At 90 d of age, the percentages of these folliclesincreasedfurther. Responseof Ovaries to ExogenousGonadotropins Table 3 shows the response of ovaries to exogenousgonadotropins.At 30 d of age, no response was observed. At 45 d of age, ovaries from only one (14%) of the gilts that had been administrated500 IU PMSG had follicles larger than 7 mm in diameter, but no ovulationpoint was observed.At 60 d of age, ovaries from two gilts (33%) administrated500 or 1000 Illof PMSG had ovulated and/or had follicles larger than 7 mm in diameter. By contrast, the ovaries of untreated gilts at the same age had no stimulated follicles. At 75 d of age, all of the ovaries respondedto the gonadotropins. The mean number of the sum of recently ovulated folliclesand follicles larger than 7 mm in diameter was 8.8 & 7.4 per gilt. Of the four untreatedgilts, two had ovarieswith corpora lutea at 75 d of age, but neither gilt ovulatednor had follicleslarger than 7 mm in diameter.
Table3. Ovarianresponsein Meishangiltsto PMSG and KG F?EG
Age (days)
(IU)
hrx
No.of gilts (IU) ~ned
3U
0 0 100tolOOO XK)
45
0 MOtolCcO
60
0 MOtolOOO
75
No. of giltshaving Body Totalno. of weight stinulated follicles Recentlyovulated (kg) gilts(%) Z7mn in dianmter follicles
11 7
6.4+1.8b 0 (0) 5.8+_0.7b 0 (0)
0 0
0 0
0 500
5 7
11.2k2.6' 0 (0) 11.8+2.8c 1 (14)
0 1 t41a
0 0
0 500
6 6
23.4k3.6 0 (0) 24.8+l.6d 2 (33)
0 1 [O to 41
0 2 [3 to 61
0 0 5COtolOOO 5UU
4 6
28.9+2.1e 0 (0) 25.O+3.od*e6(1OU)
0 5 [O to 151
0 3 [O to 121
a Figuresin bracketsrepresent the rangein the numberof follicles per gonadotropin stinulated gilt. b-e Valueswith different superscripts in the sanmcolumnare significantly different (P
APRlL 1990 VOL. 33 NO. 4
773
THERIOGENOLOGY Yorkshire gilts (9), and vesicular follicles appear at about 10 wk of age in European and American breeds (10, 14, 15). Our results suggest that vesicular follicles appear at an earlier age in Meishan gilts than in other breeds, although the appearance of secondary follicles occurs later in this breed. From 45 d of age, ovarian weight in Meishan gilts increases rapidly with an increase in the number of protruding follicles. This increase in ovarian weight with the appearance of protruding follicles is consistent with results of studies in Yorkshire gilts (9). About half of the Meishan gilts had ovaries with corpora lutea at 75 to 90 d of age, indicating that some of them had ovulated and started estrous cycles before 75 d of age. European and American breeds reach puberty at about 7 mo of age (3, 4); our results indicate that Meishan gilts reach puberty at an earlier age than other breeds. In Yorkshire gilts, ovarian development ceases for a period of about 2 mo before puberty, and this period is called the ” resting period ” (9, 16). The role of this period in the development of the ovaries is not clear. It is that the Meishan breed has no, or a very short, resting thought, however, since the ovarian weight and the number of protruding follicles period, increases from 45 d of age up to puberty. Elsaesser (17) suggested that puberty was brought about by a reduction in the intrinsic central nervous system inhibitory mechanism and/or a decrease in the negative feedback action of resulting in stimulation of pulsatile LH releasing hormone gonadal steroids, release and, consequently, of episodic LH secretion. It is possible that in Meishan gilts the central nervous system-pituitary-ovarian axis develops rapidly before puberty, and the gilts attain the onset of puberty at an early age without a resting period in ovarian development. It has been reported that a single injection of PMSG followed by a single injection of hCG induced ovulation after 100 d of age in immature crossbred gilts (18). Using the same method of administration of gonadotropins in Meishan gilts, the ovaries of only one gilt at 45 d, some gilts at 60 d, and all gilts Vesicular follicles were observed in a few at 75 d of age were stimulated. ovaries of Meishan gilts at 45 d of age in the histological examination. It has been assumed that the response of ovaries to exogenous gonadotropins occurs when the vesicular follicles appear in the ovaries of gilts (10). Our results It is suggested by this study that the precocity of support this assumption. Meishan gilts may include the development of vesicular follicles in the ovaries at an early age. REFERENCES 1.
Peilieu, C. Pig breeds. In: Peilieu, C. (ed.), Livestock China Academic Publishers, Beijing, 1984, pp. 159-168.
2.
Sasazaki,
3.
Factors affecting the natural attainment of puberty in the Hughes, P.E. gilt. In: Cole, D.J.A. and Foxcroft, G.R. (eds.), Control of Pig Reproduction, Butterworth, London, 1982, pp. 117-138.
4.
L’experimentation Legault, C. and Caritez, J.C. France. 1. Performance de reproduction en race G&et. Sel. Evol. l&:225-240 (1983).
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T. and Shimizu,
H.
Livestock
in China.
Breeds of China.
Youkendou,
Tokyo,
sur le port chinois pure et en croisement.
1984.
en
APRIL 1990 VOL. 33 NO. 4
THERIOGENOLOGY F. and Terqui,M. Sexual 5. Bazer, F.W., Thatcher,W.W., Martinat-Botte, maturationand morphologicaldevelopmentof the reproductivetract in Large White and prolificChineseMeishan pigs. J. Reprod. Fertil. a:723-728 (1988). 6. Bill, W.G. and Webb, A.J. Geneticsof Reproductionin the Pig. I&: Cole, D.J.A. and Foxcroft,G.R. (eds.), Control of Pig Reproduction, Butterworth,London, 1982, pp. 541-564. 7. Cheng, P.L. A highly prolificpig breed of China-the Taihu pig. Parts m and Iv. Pig News and Information5:13-18 (1984). F., Locatelli,A., Gruand, J., Terqui,M. and 8. Bolet, G., Martinat-Botte, Berthelot,F. Componentsof prolificacyin hyperprolificLarge White sows comparedwith the Meishan and Large White breeds. G&et. Sel. Evol. l&333-342 (1986). 9.
Dyck, G.W. and Swierstra,E.E. Growth of the reproductivetract of the gilt from birth to puberty. Can. J. Anim. Sci. a:81-87 (1983).
10.
Oxender,W.D., Colenbrander,B., van deWie1,D.F.M. and Wensing,C.J.G. Ovarian developmentin fetal and prepubertalpigs. Biol. Reprod. a:715-721 (1979).
11.
Mossman,H.W. and Duke, K.L. ComparativeMorphologyof the Mammalian Ovary. Universityof WisconsinPress, Madison,1973.
12. Hadek, R. and Getty, R. Age-changestudiesof the ovary of the domesticatedpig. Am. J. Vet. Res. a:578-584 (1959). 13. Colenbrander,B., vanRossum_Kok,C.M.J.E.,Oxender,W.D. and Wensing, C.J.G Ovarian developmentin controland decapitatedpig fetuses. Biol. Reprod. 3:217-223 (1983). 14. Casida, L.E. Prep&era1 developmentof the pig ovary and its relationto stimulationwith gonadotropichormones. Anat. Rec. a:389-396 (1935). 15. Bballa,R.C., First, N.L., Chapman,A.B. and Casida,L.E. Quantitative variationin ovarianand folliculardevelopmentin four geneticgroups of pigs at differentages. J. Anim. Sci. 3~780-784 (1969). 16. Dyck, G.W. Factors influencingsexualmaturation,pubertyand reproductive efficiencyin the gilt. Can. J. Anim. Sci. @:l-13 (1988). 17. Elsaesser,F. Endocrinecontrolof sexual maturationin the female pig and sexual differentiation of the stimulatoryoestrogenfeedbackmechanism. @: Cole, D.J.A. and Foxcroft,G.R (eds.), Control of Pig Reproduction, Butter-worth, London, 1982, pp. 93-116. 18.
Dial, G.D., Dial, O.K., Wilkinson,R.S. and Dziuk, P.J. Endocrineand ovulatoryresponsesof the gilt to exogenousgonadotropinsand estradiol during sexual maturation. Biol. Reprod. jQ:289-299(1984).
APRIL 1990 VOL. 33 NO. 4
775
DEVELOPMENT
IN
MEISBAN
PIGS
T. Miyano, J. Akamatsu,S. Kato, I. Nanjo and S. Kanda Departmentof Animal Reproduction,Faculty of Agriculture Kobe University,Kobe 657, Japan Receivedfor publication:September 8, 1989 Accepted:February 8, 1990 ABSTRACT Ovaries collected from a total of 35 Meishan gilts of various ages were morphologically and histologicallyexamined. Vesicular follicles were first observed in ovarian sections at 45 d of age. Simultaneously, protruding follicles appeared on the surface of the ovaries, and then ovarian weight increasedrapidlywith an increasingnumber of protrudingfollicles.About half of the gilts between 75 and 90 d of age had ovaries with corpora lutea, indicatingthat some of them had started estrous cycles before reaching75 d of age. In Meishan gilts treated with exogenous gonadotropins, ovaries were stimulatedas early as 45 d of age. These results suggest that the precocityof Meishan gilts may include the developmentof vesicularfolliclesin the ovaries at an early age. Key words: Meishan pig, ovary, follicle,puberty,gonadotropin INTRODUCTION China has the longest history of domesticationof pigs (1). Many types of pigs have developed, acclimating to the various regions, and at the present, more than 100 characteristic breeds are kept in the country (2). The Taihu, distributedin the ChangjiangRiver Basin, is known as a precociousand prolific breed. There are several subbreedsof the Taihu, such as the Meishan, Erhualian. Fengjing,Jiaxing and Shatou.Meishan gilts reach puberty at about 3 mo of age, whereas gilts of Europeanor Americanbreeds reach puberty at around 7 mo of age (3-5). Moreover,the average litter size for the Meishan is sixteen,whereas it is only approximatelyten for Europeanand American breeds (5-8). Puberty in female pigs has been considered to be related closely to prepubertal ovarian development. Morphological study of the ovaries of Yorkshiregilts demonstratesthat ovarianweight increasesgraduallyfrom birth to 70 d of age, then rapidly until 112 d of age with the development of vesicular follicles,after which it remains constantuntil puberty (9). Oxender et al. (10) reported from the histologicalexaminationof the ovaries of Dutch Landrace crossbred gilts that secondary follicles appeared near the time of birth and that only a few tertiary follicleswere present in the ovary at 62 to 90 d after birth. They also reported that ovarian response to exogenous gonadotropinsappeared at 9 wk of age, when tertiary folliclesappeared in the ovaries.
Acknowledgments: We thank Daiei, Inc., for supplyingthe Meishan pigs used in this study and for their financialsupport.
APRIL 1990 VOL. 33 NO. 4
769
THERIOGENOLOGY Since Meishan gilts reach puberty at an early age, their ovarian developmentmay be different from that of other breeds. The objectivesof this study were to characterize the morphological and histologicaldevelopment of ovaries and to examine the ovarian response to exogenous gonadotropins in prepubertalMeishan gilts. MATERIALSANDMETHODS A total of 35 female offspring from Meishan pigs imported to the experimentalfarm of Kobe Universityfrom the People'sRepublicof China in 1987 were used in our study. The pigs were housed under natural conditions of day length and temperatureand were weaned at 35 d of age. They were given a ration of syntheticmilk (NihonNosan Kogyo Co., Yokohama,Japan) between 7 and 80 d of age, followedby concentratefor meat productiontesting (Nihon Nosan Kogyo Co., Yokohama, Japan). Gilt ovaries were collected after the recording of body weights at 1, 30, 45, 50, 60, 75 and 90 d of age. The weights and shapes of ovaries,numbers and diametersof folliclesand of corpora lutea observedon the surface were recorded for all gilts. Immediatelyafter that, the ovaries were fixed in Bouin's fluid, embedded in paraffin wax, serially sectioned at 5Drn thickness,and stained with hematoxylinand eosin or periodicacid-Schiff(PAS) reagent. Follicular development was examined on the ovarian sections from prepubertalgilts, and follicleswere divided into the followingclasses based on the classificationby Mossman and Duke (11) : a) primordialfollicleswith a single layer of flattened pregranulosa cells, b) primary follicles with a single layer of cuboidal granulosa cells, c) secondary follicles with stratified layers of cuboidal granulosa cells, d) follicles with one or more PAS-positive Call-Exner bodies and multilayered granulosa cells, and e) vesicular follicleswith an antrum. The percentage of each class of follicles was calculated on the basis of all follicles observed on two ovarian sections having a medulla for each ovary. For the gonadotropintreatmentexperiment,a total of 26 Meishan gilts at 30, 45, 60 or 75 d of age were used. Gilts were administrated pregnant mare serum gonadotropin (PMSG; Teikoku Zoki, Tokyo, Japan) intramuscularly,at a dose of 100 to 1000 IU per gilt, followed by intramuscularadministrationof 500 IU human chorionicgonadotropin(hCG; Sankyo Zoki, Tokyo, Japan) 72 h after PMSG treatment. Then, 41 to 47 h after hCG administration, gilts were laparotomizedand the numbers of ovulationsand of follicleslarger than 7 mm in diameter were recorded for each ovary. Ovaries recovered from 26 untreated Meishan gilts at 30, 45, 60 or 75 d of age were also examined. Data for body weight, ovarian weight, and the number of follicles and corpora lutea were representedas the mean _+ standard deviation. Statistical analysiswas performedusing Student'st-test. RESULTS MorphologicalDevelopmentof Ovaries Table 1 shows the morphologicaldevelopmentof ovaries in Meishan gilts. There was no change in ovarian weight up to 30 d of age, but it increased rapidly after 45 d of age. Since various stages of ovaries were observed, they
770
APRIL 1990 VOL. 33 NO. 4
THERIOGENOLOGY were classifiedas follows: Type 1, no follicleson the surface; Type 2, fewer than five protruding follicles (larger than 2 mm in diameter);Type 3, five or more protruding follicles and a grape-like cluster appearance; and Type 4, having corpora lutea (Figure1). As shown in Table 1, all ovaries at 1 and 30 d of age were Type 1. From 45 to 60 d of age, ovaries with protruding follicles were observed.At 75 d of age, half of the gilts had ovarieswith corpora lutea, but one gilt still had a Type-l ovary. Ovaries at 90 d of age were either Type 3 or 4, and the average number of protrudingfollicleswere 33.6 + 13.6. The number of ovulated ova, that could be distinguishedfrom the number of corpora lutea at 75 and 90 d of age, was 11.5 & 1.5 and 12.0 k 1.0 per gilt that had ovulated,respectively. FollicularDevelopmentin Ovaries In the ovarian sectionsat 1 d of age, 32% of germ cells formed egg nests. As shown in Table 2, most of the folliclesobservedat this age were primordial, but a few primary follicles were present in each section. All of the oocytes surroundedby follicularcells reached the diplotene stage in meiosis. By 30 d of age, almost all of the germ cells had formed follicles,includingprimordial,
development of ovariesin Meishangilts Tab!0I..Morphological
Ase
No.of gilts
Bodv weight
(days) examined
;
Ovarian weight
hd
Cd
Xofovaries showingTypea 12
3
4
11 4
1.1+0.3c 6.4f1Jd O.O4+-O.Old 0.04t-o.o1c*d 100
0
0
0
45 50 60
4 4 5
10.5k2.5e 0.17+0.22C*e 75 16.2k2.1' l.oS+_0.51f 13 23.6k3.21 0.52+0.49e :;
0 13 :
25 74 :
0 0 0
E
4 5
36.7+4.7l 28.9+2.lh 4.26k3.268 2.31-t_2.12f*g0
0
60
49 40
Average no.b Follicles :
Corpora lutea
d c,d
2.5f 4.3c*e 14.6+ 9.3f,g 6 4-+ 7.7e*f
0 oc
c,d
0 0 0
;*; c:d
30:8+27.4grh2.9f3.0e 33.6+13.6h 2.4+3.6d*e
a Type 1, ovarywith no follicleon the surface; Type 2, ovarywith lessthan five protruding follicles; Type 3, ovarywith fiveor more protruding follicles; Type 4, ovarywith corporalutea.See alsoFigure1. b Eachvaluerepresents the mean -t S.D.per ovary. c-lValueswith different superscripts in the samscohnnnare significantly different (P
Age (days)
follicles % of No. of with Call-Exner follicles Vesicular shapea examined Prmmxdial Primary Secondary body
Ovarian
1 xl 45-60 90
Type1 zz;
11,082 18,684
99.2 94.7
0.8 3.1
2.0
0.2
5,237 2,741 4,121 889
89.4 81.5 85.5 81.7
3.1 4.7 2.1 1.7
E 317 1.6
2.8 4.7 5.8 7.4
::: 2.7 7.6
a See footnote"a" in Table1.
APRIL 1990 VOL. 33 NO. 4
771
THERIOGENOLOGY
Figure 1. Various categoriesof ovariandevelopmentin Meishan gilts: a) Type 1, 30 days of age, with no protrudingfollicleson the surface;b) Type 2, 60 days of age, showingonly one large vesicularfollicle; c) Type 3, 60 days of age with five or more protrudingfollicleson the surface;and d) Type 4, 75 days of age with corpora lutea.
772
APRIL 1990 VOL. 33 NO. 4
THERIOGENOLOGY primary and secondaryfolliclesand follicleswith Call-Rxnerbodies. There was no egg nest in the ovarian sections.Vesicularfollicleswere first observed in the ovaries at 45 d of age. Follicular development was summarized in each category of ovary from 45 d to 60 d of age. The percentagesof follicleswith Call-Rxnerbodies and vesicular folliclesincreasedas the shape of the ovaries proceeded from Type 1 to Type 3. At 90 d of age, the percentages of these folliclesincreasedfurther. Responseof Ovaries to ExogenousGonadotropins Table 3 shows the response of ovaries to exogenousgonadotropins.At 30 d of age, no response was observed. At 45 d of age, ovaries from only one (14%) of the gilts that had been administrated500 IU PMSG had follicles larger than 7 mm in diameter, but no ovulationpoint was observed.At 60 d of age, ovaries from two gilts (33%) administrated500 or 1000 Illof PMSG had ovulated and/or had follicles larger than 7 mm in diameter. By contrast, the ovaries of untreated gilts at the same age had no stimulated follicles. At 75 d of age, all of the ovaries respondedto the gonadotropins. The mean number of the sum of recently ovulated folliclesand follicles larger than 7 mm in diameter was 8.8 & 7.4 per gilt. Of the four untreatedgilts, two had ovarieswith corpora lutea at 75 d of age, but neither gilt ovulatednor had follicleslarger than 7 mm in diameter.
Table3. Ovarianresponsein Meishangiltsto PMSG and KG F?EG
Age (days)
(IU)
hrx
No.of gilts (IU) ~ned
3U
0 0 100tolOOO XK)
45
0 MOtolCcO
60
0 MOtolOOO
75
No. of giltshaving Body Totalno. of weight stinulated follicles Recentlyovulated (kg) gilts(%) Z7mn in dianmter follicles
11 7
6.4+1.8b 0 (0) 5.8+_0.7b 0 (0)
0 0
0 0
0 500
5 7
11.2k2.6' 0 (0) 11.8+2.8c 1 (14)
0 1 t41a
0 0
0 500
6 6
23.4k3.6 0 (0) 24.8+l.6d 2 (33)
0 1 [O to 41
0 2 [3 to 61
0 0 5COtolOOO 5UU
4 6
28.9+2.1e 0 (0) 25.O+3.od*e6(1OU)
0 5 [O to 151
0 3 [O to 121
a Figuresin bracketsrepresent the rangein the numberof follicles per gonadotropin stinulated gilt. b-e Valueswith different superscripts in the sanmcolumnare significantly different (P
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THERIOGENOLOGY Yorkshire gilts (9), and vesicular follicles appear at about 10 wk of age in European and American breeds (10, 14, 15). Our results suggest that vesicular follicles appear at an earlier age in Meishan gilts than in other breeds, although the appearance of secondary follicles occurs later in this breed. From 45 d of age, ovarian weight in Meishan gilts increases rapidly with an increase in the number of protruding follicles. This increase in ovarian weight with the appearance of protruding follicles is consistent with results of studies in Yorkshire gilts (9). About half of the Meishan gilts had ovaries with corpora lutea at 75 to 90 d of age, indicating that some of them had ovulated and started estrous cycles before 75 d of age. European and American breeds reach puberty at about 7 mo of age (3, 4); our results indicate that Meishan gilts reach puberty at an earlier age than other breeds. In Yorkshire gilts, ovarian development ceases for a period of about 2 mo before puberty, and this period is called the ” resting period ” (9, 16). The role of this period in the development of the ovaries is not clear. It is that the Meishan breed has no, or a very short, resting thought, however, since the ovarian weight and the number of protruding follicles period, increases from 45 d of age up to puberty. Elsaesser (17) suggested that puberty was brought about by a reduction in the intrinsic central nervous system inhibitory mechanism and/or a decrease in the negative feedback action of resulting in stimulation of pulsatile LH releasing hormone gonadal steroids, release and, consequently, of episodic LH secretion. It is possible that in Meishan gilts the central nervous system-pituitary-ovarian axis develops rapidly before puberty, and the gilts attain the onset of puberty at an early age without a resting period in ovarian development. It has been reported that a single injection of PMSG followed by a single injection of hCG induced ovulation after 100 d of age in immature crossbred gilts (18). Using the same method of administration of gonadotropins in Meishan gilts, the ovaries of only one gilt at 45 d, some gilts at 60 d, and all gilts Vesicular follicles were observed in a few at 75 d of age were stimulated. ovaries of Meishan gilts at 45 d of age in the histological examination. It has been assumed that the response of ovaries to exogenous gonadotropins occurs when the vesicular follicles appear in the ovaries of gilts (10). Our results It is suggested by this study that the precocity of support this assumption. Meishan gilts may include the development of vesicular follicles in the ovaries at an early age. REFERENCES 1.
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