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Comparative studies on the effectiveness of Sil-estrus implants, Veramix sheep sponges and prostaglandin F2α in synchronizing estrus in West African dwarf sheep
THERIOGENOLOGY
COMPARATIVE STUDIESON THF EFFFCTIVENESS OF SIL-ESTRUS IMPLANTS, VERAMIX SHEEPSPONGESAND PROSTAGLANDIN FM IN SYNCHRONIZING ESTRUSIN WEST AFRICANDWARFSHEEP M.O. Akusu2and G.N. Egbunikelg" G.O. Oyedijil, 'Department of AnimalScienceand departmentof Veterinary Surgeryand Reproduction, University of Ibadan Nigeria F&eceived for publication: February 3, 1990 Accepted:July 2, 1990 ABSTRACT Sil-estrus implants, Veramixspongesand PGF2* were successfully used to synchronize estrusin normocyclic West Africandwarfsheep. The intervalsfromend of treatmentto onsetof observable estrusin the threegroupsof treatment were 42.33+ 1.99,77.67 + 15.20and 41.62+ 2.23h respectively, for Sil-estrus, veramixspongezand PGF2oC(p)U.G5). Of all the treatedsheep,10% of thosetreatedwith Sil-estrus and PGFa and 66.6% of the sheeptreatedwith Veramixspongeswere in estruswithin48 h post treatment.Neitherthe durationof standing estrusnor the succeeding estruscyclelengthwas significantly affected by the treatment.Theseresultsindicatethat progestogens and prostaglandinF2OC can be usefullyemployedin the management of reproduction of West Africandwarfsheep. Key words: Estrussynchronization, Sil-estrus implants, Veramix sponges,PGF2& , sheep INTRODUCTION Estrussynchronization has beccmea vitalinstrument in the management of reproduction in domesticanimals. Its benefitsincludea planned breedingprogramne and a reductionin laborcostsin termsof estrus detection and care of the newborn. Whileestrussynchronization has beenused widelyin artificial insemination programs,it has not been practiced extensively in handmatedherds. It wouldalso be convenient for the smallfarmer. Estrussynchronization has also becomean important tool for the studyof reproductive physiology and embryotransfer. Variousprogestogens have beenused in the regulation of the estrous cyclein sheep. They are administered orallyor intravenously, incorporatedinto silasticimplants, or impregnated into vaginalsponges(I-5). Ewes are usuallytreatedfor 14 to 16 d to preventfollicular formation and ovulation.Estrusis synchronized at varioustimesfollowingthe Acknowledgements We wish to thankTogopharma NigeriaLimitedfor the generousgift of Lutalyse(PGF2Qc1. The standardcanmercial sheepand goat ration was obtainedfranLivestockFeedsLtd.,Pfizer,Lagos a Correspondence Addressto G.N.Egbunike. SEPTEMBER WSOVOL. 34 NO. 3
613
THERIOGENOLOGY
to estrus termination of treatment.The intervalfromend of treatment has beenreportedto be shortened when pregnantmare serumgonadotrophin (PM%) is administered (61,whileovulationtime is facilitated by the administration of humanchorionic gonadotrophin (hCG;7) at the end of treatment. Sinceprostaglandin F2y has been recognized as the luteolysin in the ewe (8,91, it has been used in syochronizing estrusin this Species of PGF2e or its with encouraging results(10,11). Two administrations analogueduringmidcycleensuresa high degreeof synchrony and a return to estrus(12). Estrussynchronization trialsin goatsand cattlein Nigeriahave used PGF2q (13,14). The objectives of our studywere to evaluatethe effectiveness of two progestogens (Sil-estrus implantsand Veramixsheepsponges), and a PGF20(analogue(Lutalyse) in synchronizing estrusin the West African dwarfsheepin southwestern Nigeria. The breedis foundpredominantly in the humidzone. It is a meat breed,usuallywhitein colorand attainsan averagematureweightof about36 kg (15). MATERIALSANDMETBODS Eighteenpluriparous normocyclic West Africandwarfewes,aged 4 to 5 yr and weighing20 to 40 kg, were assignedinto threegroupsof six ewes per groupafterequalization of weights. The eweswere housedin roofedconcretefloor-pens with low woodenwalls. Theywere fed a standardcmercial palm-kernel cake-based sheepand goat rationat the rate of 1 kg per ewe per day. Waterand freshgiantstargrass (Cynodon plectostachyum) were suppliedad libitum. The dailydry-bulb temperature and relativehumidityin the barnduringthe experiment (January to June, 19891rangedfrom 26 to 310Cand 46 to 83, respectively. GroupA ewes were each givenPGF2CC(Dinoprost Tranethamine, Upjohn Canpany,Kalamazoo, US A ; 10 ng i.m.1at 11-dinterval.GroupB ewes receiveda subcutaneous implantof Sil-estrus(AbbottLaboratories, S.A. Athens,Greece)containing 375 mg progesterone in a siliconeelastomer matrix. GroupC eweswere treatedwith Veramixsheepsponges(Upjohn Ltd. FlemingWay, Crawley,Sussex,England)containing 60 mg 6-methyl-17acetoxy-progesterone. Spongeswere insertedin the anteriorvagina. Both implantsand spongeswere removed14 d later. Ewes were exposedfour timesdaily (0600,1200,1800and 2400h) post treatmentto matureapronedrams. The durationof standingestrus was assessedas reportedearlier(131,whilethe lengthof the estrous cyclewas regardedas the intervalfromthe end of estrusto the beginning of the next one in the same ewe. Data were subjectedto one-wayanalysisof varianceand Student's t-testfor the establishment of significance.
614
SEPTEMBER 1660 VOL. 34 NO. 3
THERIOGENOLOGY
RESULTS Neitherspongesnor implantswere lostduringthe treatment period. The spongeswere not infected, althoughtherewas sanedegreeof vaginal mucousmattingof the sponges. Estruswas synchronized in all ewes by the threetreatment methods. The mean + standarderrorof the mean intervalfrcxn treatmentto the onsetof G&us was 41.67+ 2.22h (36 to 48 h) in the P@ 4c ewes,while the corresponding valuesf% Sil-estrus and spongeswere 45.33f 1.96h (36 to 48 h) and 77.67+ 15.20h (48 to 150h), respectivelyfpYO.05). Ewes differedin the i&rval betweentreatment and Onsetof estrus irrespective of treatment. Estruswas not observedin any of the ewes duringthe first 24 h posttreatment.All ewes treatedwith PCF2& and Sil-estrus implants were in estruswithin48 h post treatment whereasone of the ewes treatedwith a Veramixspongewas in estrusduringthisperiod. All the rest of the ewes in the VeramiXsponggroupwere in estrus72 h post treatment. Figures1 and 2 summarize estrusdurationand estrouscyclelength respectively, in the threetreatment groupsduringthreesuccessive cycles. Estrouscyclelengthswere generallyshorterin ewes treated with Sil-estrus implants(P>O.O5)than the othertwo groups. Therewas no difinitetrendin estrouscyclelengthand estrusdurationin PCF2w and Veramixsponge- treatedewes. The over all mean + standarderror of mean for all the ewes showedthat estrouscyclelen-&hincreasedfrom 16.61+ 0.70 d duringthe imnediatepost treatment estrus(CCL I) to 17.067 0.71 and167.B3 +,O-i24 d duringthe second(CCL2) and third (CCL 3) estks, respectively:The Mediate post treatment estrusduration was shorterfor each treatment groupthan the subsequent estrusduration but the differences were not statistically significant. DISCUSSION The threeestrussynchronizing meMods effectively synchronized estrusin the West Africandwarfsheep. The high degreeof synchrony achievedwith the progestogens has been reportedby otherworkers(2, 6, 161. The variationin the onsetof estrusat the termination of treatment by individual eweswas similarto previousreports(4, 17). This variationcouldhave resultedfrom the properties of each of the progestogens used and the methodof administration (10,11, 18, 19). The degreeof synchronyand the intervalto estrusfollowingthe second administration were consistent with earlierstudies(12,20, 21). EF2 The nonsignificant difference in estrusdurationin the threegroups showedthat standingestruswas not affectedby treatment.Similarly, estrouscyclelengthswere canparable in all treatmentgroups,and were withinnormallengthsreportedfor some breedsof sheep (22). Alghough fertilitytrials were not determinedin this study,reportsindicated that fertilityof PGF& treatedewes (IO)and goats (13)are canparable to that of the controls.The poor fertilityat progestogen-induced estrusis reportedto be due to the disturbance in spermtransportand survivalin the femalegenitaltract (23). It is unlikelythat fertility will be affectedin naturalservice,whichensuresadequatespermatozoa
SEPTEMBER 1990 VOL. 34 NO. 3
615
THERIOGENOLOGY
Figure 1.
Estrus duration (OD) in West African dwarf sheep followingsynchronization with three differentdrugs.
Figure 2.
Estrous cycle length (OCL) in West African dwarf sheep followingsynchronization with three differentdrugs.
616
SEPTEMBER 1990 VOL. 34 NO. 3
THERIOGENOLOGY
rateswere achieved(3,24) in the femaletract. Hencehigherfertility in the groupof ewes inseminated with higherspermconcentration and with freshsemen. It is concludedfromtheseobservations thatprogestogens and PGF2w are suitableagentsfor synchronizing estrusin West Africandwarfsheep. Therefore, the choiceof eitheragentsand methodswill dependon access to drugsas well as on economicconsiderations. However,the ease of administration of PGF20&makes it a clearchoicein estroussynchronizationprograms. REFERENCES 7.
on estrus Foote,W.C. and Waite,A.B. Some effectsof progesterone behaviour and fertility in the ewe J. Anim.Sci.24:151-155(1965).
2.
of medroxyDeweese,W.P.,Glimp,H.A. and Dutt,R.H. Comparison progesterone acetateorallyand in vaginalspongesfor synchronizing estrusin ewes. J. Anim.Sci.-31:394-397(1970).
3.
ewes inseminated with Colas,G. Fertilityin progestogen-treated freshor frozensemenin the breedingseason. VIIthInt.Cong. Anim.Reprod.and AI. pp.164-165(1972).
4.
Veradin,M., Nesic, L. and Pavlovic, A. The use of progestogencontaining vaginalpessariesin stimulating estrusin sheep. I. Synchronization of estrusin matingseason. Veterinaria Yugoslavia g:439-448 ('19731.
5.
D. The fertility of Tsakalof, P., Vlachos,N. and Latousakis, nulliparous anestrusewes synchronized for estruslate in autumn, afterthe end of the breedingseason. Proc.Int.Symp.Physiopath. Reprod.and AI. in SmallRuminants.pp.69-73(1974).
6.
Eastwood,K.C. and MacDonald, M.F. Maintenance of estroussynchronizationin Z-year-old ewes at secondheat afterprogestogen sponge treatment.NZ J. Agri.Res. 18:119-121 (1975).
7.
Dziuk,P-J., Cook,B., Niswender, C.D.,Kaltenbach, C.C.and Doane, B.B. Inhibition and controlof estrusand ovulationin eweswith a subcutaneous implantof Siliconerubberimpregnated with progestogen. Amer.J. Vet. Res.9:2415-2477(1968).
8.
Hearnshaw, H., Restall,B.J. and Gleeson,D.R. Observations on the luteolytic effectof PGF20(duringthe estrouscycleand earlypregnancyin the ewe. J. Reprod.Fertil.-32:322abstract(1973).
9.
Goding,J.R. The demonstration thatPGF2oLis the uterineluteolysinin the ewe. J. Reprod.Fertil.38:261-271(1974).
10. Haresign, W. Controlled breedingin sheepusingthe prostaglandin analogueICI 80996. Anim.Prod.22:137abstract(1976). 11.
Thimonier, J. Hormonalcontrolof estrouscyclein the sheep (a review). LivestockProd.Sci.6:36-50(1979).
SEPTEMBER 1990 VOL. 34 NO. 3
617
THERIOGENOLOGY 12.
Acritopoulou, S., Haresign, W., Foster,J.P.and Lamoing,G.P. Plasmaprogesterone and LH concentrations in ewesafterinjection of an analogueof PGF2w. J. Reprod.Fertil.49:337-340(1977).
13.
A~LE.u,M.O. and Egbunike, G.N.
14.
V. and Kumi-Diaka, J. Voh, A.A.,Jr.,Qyedipe,E.O. Buvanendran, Estrusresponseof indigenous NigerianZebu cattleafterPGF2# treatment undercontinuous observation for two seasons. Theriogenologyg:77-79 (1987).
15.
Williamson, G. and Payne,W.J.A. SheepBreeds. In: Williamson, G. and Payne,W.J.A.teds),An Introduction to AnimalHusbandryin the tropics. ELBS and Longman,Essex,England1978,pp.442-443.
16.
C. and Duque,M. Controlof the estrous Mazzarri,G.B.,Fuenmayor, cyclein ewes by meansof vaginalspongesimpregnated with fluorogestone acetate. Agron.Trop.23:315-321(1973).
17.
Wishart,D.F. Synchronization of estrusin sheep. The use of pessaries.Vet. Rec.8_l:276-287 (1967).
18.
to controlthe estrouscycle Corteel,J.M. The use of progestogens of the dairygoat. Annls.Biol.Anim.Biochem.Biophys.2:353-363
Fertilityof the West Africandwarf goat in its nativeenvironment following PGF% inducedestrus. Vet.Quart.5:173-176(1984).
(1975). 19.
Robertson, H.A. Reproduction in the ewe and the goat. In: Cole, H.H. and Cupps,P.T. teds.), Reproduction in DanesticAnimals. AcademicPress,New York, 1977,pp.477-498.
20.
Acritopoulou, S., Haresign, W. and Lamming,G.E. Timeof ovulation in ewes aftertreatment with a PGF20(, analogue.J. Reprod.Fertil. (1978). -54:189-191
21.
Haresign, W. Ovulationcontrolin the sheep. In: Cryghton, D.B., Haynes,N.B.,Foxcroft,G.R. and Lamning,G.E. teds),Controlof Ovulation, Butterworth, London,1978,pp.435-451.
22.
Deans,D.W.,Laing,J.A.,Malrose,D.R.,Reed,H.C.and Vandeplassche, M. The management of ovarianfunction.In: Laing, J.A. ted),Fertilityand Infertility in Daestic Animals,ELBSand BailliereTindall,London,1978,pp.108-136.
23.
Quinlivan, T.D. and Robinson, T.J. Numbersof spermatozoa in the genitaltractafterAI of progesterone-treated ewes. J. Reprod. Fertil.x:73-86 (1969).
24.
Allison,A.J. and Robinson,T.J. Fertilityof progestogen-treated ewes in relationto the numberand concentration of spermatozoa in the inseminate.Austr.J. Biol.Sci.24:1001-1008 (1971).
618
SEPTEMBER 1990 VOL. 34 NO. 3
COMPARATIVE STUDIESON THF EFFFCTIVENESS OF SIL-ESTRUS IMPLANTS, VERAMIX SHEEPSPONGESAND PROSTAGLANDIN FM IN SYNCHRONIZING ESTRUSIN WEST AFRICANDWARFSHEEP M.O. Akusu2and G.N. Egbunikelg" G.O. Oyedijil, 'Department of AnimalScienceand departmentof Veterinary Surgeryand Reproduction, University of Ibadan Nigeria F&eceived for publication: February 3, 1990 Accepted:July 2, 1990 ABSTRACT Sil-estrus implants, Veramixspongesand PGF2* were successfully used to synchronize estrusin normocyclic West Africandwarfsheep. The intervalsfromend of treatmentto onsetof observable estrusin the threegroupsof treatment were 42.33+ 1.99,77.67 + 15.20and 41.62+ 2.23h respectively, for Sil-estrus, veramixspongezand PGF2oC(p)U.G5). Of all the treatedsheep,10% of thosetreatedwith Sil-estrus and PGFa and 66.6% of the sheeptreatedwith Veramixspongeswere in estruswithin48 h post treatment.Neitherthe durationof standing estrusnor the succeeding estruscyclelengthwas significantly affected by the treatment.Theseresultsindicatethat progestogens and prostaglandinF2OC can be usefullyemployedin the management of reproduction of West Africandwarfsheep. Key words: Estrussynchronization, Sil-estrus implants, Veramix sponges,PGF2& , sheep INTRODUCTION Estrussynchronization has beccmea vitalinstrument in the management of reproduction in domesticanimals. Its benefitsincludea planned breedingprogramne and a reductionin laborcostsin termsof estrus detection and care of the newborn. Whileestrussynchronization has beenused widelyin artificial insemination programs,it has not been practiced extensively in handmatedherds. It wouldalso be convenient for the smallfarmer. Estrussynchronization has also becomean important tool for the studyof reproductive physiology and embryotransfer. Variousprogestogens have beenused in the regulation of the estrous cyclein sheep. They are administered orallyor intravenously, incorporatedinto silasticimplants, or impregnated into vaginalsponges(I-5). Ewes are usuallytreatedfor 14 to 16 d to preventfollicular formation and ovulation.Estrusis synchronized at varioustimesfollowingthe Acknowledgements We wish to thankTogopharma NigeriaLimitedfor the generousgift of Lutalyse(PGF2Qc1. The standardcanmercial sheepand goat ration was obtainedfranLivestockFeedsLtd.,Pfizer,Lagos a Correspondence Addressto G.N.Egbunike. SEPTEMBER WSOVOL. 34 NO. 3
613
THERIOGENOLOGY
to estrus termination of treatment.The intervalfromend of treatment has beenreportedto be shortened when pregnantmare serumgonadotrophin (PM%) is administered (61,whileovulationtime is facilitated by the administration of humanchorionic gonadotrophin (hCG;7) at the end of treatment. Sinceprostaglandin F2y has been recognized as the luteolysin in the ewe (8,91, it has been used in syochronizing estrusin this Species of PGF2e or its with encouraging results(10,11). Two administrations analogueduringmidcycleensuresa high degreeof synchrony and a return to estrus(12). Estrussynchronization trialsin goatsand cattlein Nigeriahave used PGF2q (13,14). The objectives of our studywere to evaluatethe effectiveness of two progestogens (Sil-estrus implantsand Veramixsheepsponges), and a PGF20(analogue(Lutalyse) in synchronizing estrusin the West African dwarfsheepin southwestern Nigeria. The breedis foundpredominantly in the humidzone. It is a meat breed,usuallywhitein colorand attainsan averagematureweightof about36 kg (15). MATERIALSANDMETBODS Eighteenpluriparous normocyclic West Africandwarfewes,aged 4 to 5 yr and weighing20 to 40 kg, were assignedinto threegroupsof six ewes per groupafterequalization of weights. The eweswere housedin roofedconcretefloor-pens with low woodenwalls. Theywere fed a standardcmercial palm-kernel cake-based sheepand goat rationat the rate of 1 kg per ewe per day. Waterand freshgiantstargrass (Cynodon plectostachyum) were suppliedad libitum. The dailydry-bulb temperature and relativehumidityin the barnduringthe experiment (January to June, 19891rangedfrom 26 to 310Cand 46 to 83, respectively. GroupA ewes were each givenPGF2CC(Dinoprost Tranethamine, Upjohn Canpany,Kalamazoo, US A ; 10 ng i.m.1at 11-dinterval.GroupB ewes receiveda subcutaneous implantof Sil-estrus(AbbottLaboratories, S.A. Athens,Greece)containing 375 mg progesterone in a siliconeelastomer matrix. GroupC eweswere treatedwith Veramixsheepsponges(Upjohn Ltd. FlemingWay, Crawley,Sussex,England)containing 60 mg 6-methyl-17acetoxy-progesterone. Spongeswere insertedin the anteriorvagina. Both implantsand spongeswere removed14 d later. Ewes were exposedfour timesdaily (0600,1200,1800and 2400h) post treatmentto matureapronedrams. The durationof standingestrus was assessedas reportedearlier(131,whilethe lengthof the estrous cyclewas regardedas the intervalfromthe end of estrusto the beginning of the next one in the same ewe. Data were subjectedto one-wayanalysisof varianceand Student's t-testfor the establishment of significance.
614
SEPTEMBER 1660 VOL. 34 NO. 3
THERIOGENOLOGY
RESULTS Neitherspongesnor implantswere lostduringthe treatment period. The spongeswere not infected, althoughtherewas sanedegreeof vaginal mucousmattingof the sponges. Estruswas synchronized in all ewes by the threetreatment methods. The mean + standarderrorof the mean intervalfrcxn treatmentto the onsetof G&us was 41.67+ 2.22h (36 to 48 h) in the P@ 4c ewes,while the corresponding valuesf% Sil-estrus and spongeswere 45.33f 1.96h (36 to 48 h) and 77.67+ 15.20h (48 to 150h), respectivelyfpYO.05). Ewes differedin the i&rval betweentreatment and Onsetof estrus irrespective of treatment. Estruswas not observedin any of the ewes duringthe first 24 h posttreatment.All ewes treatedwith PCF2& and Sil-estrus implants were in estruswithin48 h post treatment whereasone of the ewes treatedwith a Veramixspongewas in estrusduringthisperiod. All the rest of the ewes in the VeramiXsponggroupwere in estrus72 h post treatment. Figures1 and 2 summarize estrusdurationand estrouscyclelength respectively, in the threetreatment groupsduringthreesuccessive cycles. Estrouscyclelengthswere generallyshorterin ewes treated with Sil-estrus implants(P>O.O5)than the othertwo groups. Therewas no difinitetrendin estrouscyclelengthand estrusdurationin PCF2w and Veramixsponge- treatedewes. The over all mean + standarderror of mean for all the ewes showedthat estrouscyclelen-&hincreasedfrom 16.61+ 0.70 d duringthe imnediatepost treatment estrus(CCL I) to 17.067 0.71 and167.B3 +,O-i24 d duringthe second(CCL2) and third (CCL 3) estks, respectively:The Mediate post treatment estrusduration was shorterfor each treatment groupthan the subsequent estrusduration but the differences were not statistically significant. DISCUSSION The threeestrussynchronizing meMods effectively synchronized estrusin the West Africandwarfsheep. The high degreeof synchrony achievedwith the progestogens has been reportedby otherworkers(2, 6, 161. The variationin the onsetof estrusat the termination of treatment by individual eweswas similarto previousreports(4, 17). This variationcouldhave resultedfrom the properties of each of the progestogens used and the methodof administration (10,11, 18, 19). The degreeof synchronyand the intervalto estrusfollowingthe second administration were consistent with earlierstudies(12,20, 21). EF2 The nonsignificant difference in estrusdurationin the threegroups showedthat standingestruswas not affectedby treatment.Similarly, estrouscyclelengthswere canparable in all treatmentgroups,and were withinnormallengthsreportedfor some breedsof sheep (22). Alghough fertilitytrials were not determinedin this study,reportsindicated that fertilityof PGF& treatedewes (IO)and goats (13)are canparable to that of the controls.The poor fertilityat progestogen-induced estrusis reportedto be due to the disturbance in spermtransportand survivalin the femalegenitaltract (23). It is unlikelythat fertility will be affectedin naturalservice,whichensuresadequatespermatozoa
SEPTEMBER 1990 VOL. 34 NO. 3
615
THERIOGENOLOGY
Figure 1.
Estrus duration (OD) in West African dwarf sheep followingsynchronization with three differentdrugs.
Figure 2.
Estrous cycle length (OCL) in West African dwarf sheep followingsynchronization with three differentdrugs.
616
SEPTEMBER 1990 VOL. 34 NO. 3
THERIOGENOLOGY
rateswere achieved(3,24) in the femaletract. Hencehigherfertility in the groupof ewes inseminated with higherspermconcentration and with freshsemen. It is concludedfromtheseobservations thatprogestogens and PGF2w are suitableagentsfor synchronizing estrusin West Africandwarfsheep. Therefore, the choiceof eitheragentsand methodswill dependon access to drugsas well as on economicconsiderations. However,the ease of administration of PGF20&makes it a clearchoicein estroussynchronizationprograms. REFERENCES 7.
on estrus Foote,W.C. and Waite,A.B. Some effectsof progesterone behaviour and fertility in the ewe J. Anim.Sci.24:151-155(1965).
2.
of medroxyDeweese,W.P.,Glimp,H.A. and Dutt,R.H. Comparison progesterone acetateorallyand in vaginalspongesfor synchronizing estrusin ewes. J. Anim.Sci.-31:394-397(1970).
3.
ewes inseminated with Colas,G. Fertilityin progestogen-treated freshor frozensemenin the breedingseason. VIIthInt.Cong. Anim.Reprod.and AI. pp.164-165(1972).
4.
Veradin,M., Nesic, L. and Pavlovic, A. The use of progestogencontaining vaginalpessariesin stimulating estrusin sheep. I. Synchronization of estrusin matingseason. Veterinaria Yugoslavia g:439-448 ('19731.
5.
D. The fertility of Tsakalof, P., Vlachos,N. and Latousakis, nulliparous anestrusewes synchronized for estruslate in autumn, afterthe end of the breedingseason. Proc.Int.Symp.Physiopath. Reprod.and AI. in SmallRuminants.pp.69-73(1974).
6.
Eastwood,K.C. and MacDonald, M.F. Maintenance of estroussynchronizationin Z-year-old ewes at secondheat afterprogestogen sponge treatment.NZ J. Agri.Res. 18:119-121 (1975).
7.
Dziuk,P-J., Cook,B., Niswender, C.D.,Kaltenbach, C.C.and Doane, B.B. Inhibition and controlof estrusand ovulationin eweswith a subcutaneous implantof Siliconerubberimpregnated with progestogen. Amer.J. Vet. Res.9:2415-2477(1968).
8.
Hearnshaw, H., Restall,B.J. and Gleeson,D.R. Observations on the luteolytic effectof PGF20(duringthe estrouscycleand earlypregnancyin the ewe. J. Reprod.Fertil.-32:322abstract(1973).
9.
Goding,J.R. The demonstration thatPGF2oLis the uterineluteolysinin the ewe. J. Reprod.Fertil.38:261-271(1974).
10. Haresign, W. Controlled breedingin sheepusingthe prostaglandin analogueICI 80996. Anim.Prod.22:137abstract(1976). 11.
Thimonier, J. Hormonalcontrolof estrouscyclein the sheep (a review). LivestockProd.Sci.6:36-50(1979).
SEPTEMBER 1990 VOL. 34 NO. 3
617
THERIOGENOLOGY 12.
Acritopoulou, S., Haresign, W., Foster,J.P.and Lamoing,G.P. Plasmaprogesterone and LH concentrations in ewesafterinjection of an analogueof PGF2w. J. Reprod.Fertil.49:337-340(1977).
13.
A~LE.u,M.O. and Egbunike, G.N.
14.
V. and Kumi-Diaka, J. Voh, A.A.,Jr.,Qyedipe,E.O. Buvanendran, Estrusresponseof indigenous NigerianZebu cattleafterPGF2# treatment undercontinuous observation for two seasons. Theriogenologyg:77-79 (1987).
15.
Williamson, G. and Payne,W.J.A. SheepBreeds. In: Williamson, G. and Payne,W.J.A.teds),An Introduction to AnimalHusbandryin the tropics. ELBS and Longman,Essex,England1978,pp.442-443.
16.
C. and Duque,M. Controlof the estrous Mazzarri,G.B.,Fuenmayor, cyclein ewes by meansof vaginalspongesimpregnated with fluorogestone acetate. Agron.Trop.23:315-321(1973).
17.
Wishart,D.F. Synchronization of estrusin sheep. The use of pessaries.Vet. Rec.8_l:276-287 (1967).
18.
to controlthe estrouscycle Corteel,J.M. The use of progestogens of the dairygoat. Annls.Biol.Anim.Biochem.Biophys.2:353-363
Fertilityof the West Africandwarf goat in its nativeenvironment following PGF% inducedestrus. Vet.Quart.5:173-176(1984).
(1975). 19.
Robertson, H.A. Reproduction in the ewe and the goat. In: Cole, H.H. and Cupps,P.T. teds.), Reproduction in DanesticAnimals. AcademicPress,New York, 1977,pp.477-498.
20.
Acritopoulou, S., Haresign, W. and Lamming,G.E. Timeof ovulation in ewes aftertreatment with a PGF20(, analogue.J. Reprod.Fertil. (1978). -54:189-191
21.
Haresign, W. Ovulationcontrolin the sheep. In: Cryghton, D.B., Haynes,N.B.,Foxcroft,G.R. and Lamning,G.E. teds),Controlof Ovulation, Butterworth, London,1978,pp.435-451.
22.
Deans,D.W.,Laing,J.A.,Malrose,D.R.,Reed,H.C.and Vandeplassche, M. The management of ovarianfunction.In: Laing, J.A. ted),Fertilityand Infertility in Daestic Animals,ELBSand BailliereTindall,London,1978,pp.108-136.
23.
Quinlivan, T.D. and Robinson, T.J. Numbersof spermatozoa in the genitaltractafterAI of progesterone-treated ewes. J. Reprod. Fertil.x:73-86 (1969).
24.
Allison,A.J. and Robinson,T.J. Fertilityof progestogen-treated ewes in relationto the numberand concentration of spermatozoa in the inseminate.Austr.J. Biol.Sci.24:1001-1008 (1971).
618
SEPTEMBER 1990 VOL. 34 NO. 3