Plasma gonadotropin and progesterone concentrations during the estrous cycle of Finn, Suffolk and Targhee ewes

THERIOGENOLOGY

PLASMAGoNADCTROPINANDPRa3ESIERCNECCNCEt?IRATIoNS DURING TBEE.STROUSCYCLEOFFINN,SUFFOLKANDTARGHEEEWES J.E. Wheaton,J.M. Marchek,H.A. Hamra and S.N. Al-Raheem Departmentof Animal Science Universityof Minnesota 55108 St. Paul, MN Receivedfor publication: JULY 22, 1987 Accepted:May 3, 1988

Hormonalprofilesduring the estrouscycle of Finn, Suffolkand Targheeewes were canparedin six ewes of each breed. Blood samples Were drawn by venipunctureat 8-h intervalsfran onset to onset of consecutiveestrousperiods. Nun&r of corporalutea (CL) and ovarian follicles23 m in diameteron Day 10 (estrus= Day 0) wre observed using endoscapy. Estrous cycle lengthWas 14.9, 15.6 and 16.4 d (PO.l)in Finn, Suffolkand Targheeewss, respectively. Results indicatethat the higher ovulationrate of the Finn ewe is not elicitedby increasedESH levels at any stage of the estrouscycle. Key Words: sheep,gonadotropins, ovulationrate, estrouscycle Acknowledgments Appreciationis expressedto Dr. G.D. N&mender for providingLH antiserumand to Dr. L.E. Reichert,Jr., for the highly purifiedwine LH for radioiodination.Antiserumto ovine FSH was a gift fran the USDAAuimal HormoneProgram. Ovine IH and FSH referencepreparations and wine FSH for radioicdination wre suppliedby the National Hormoneand PituitaryProgram,Universityof MarylandSchool of Medicine,NIADDK. The authorsthank W. Effler,T. Knudson and C. Youngs for their technicalassistance. Reprint requests: Departmentof Animal Science,495 Animal Sciencefleterinarv MedicineBldc.. _. 1988 Fitch Ave.. St. Paul. MN 55108. Publishedas paper No. 00,000of the scientificjournalseries of the Minnesota AgriculturalExperimentStationon researchconducted under MiMeSOta AgriculturalExperimentStationProjectNo. 0302-4816-75.

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I??IRODlJCl!IoN Ovulationrates of one to two are typicalof most breeds of sheep. Prolificsheep breeds,which includethe RussianRamnov, MoroccanD'Man and FinnishLandrace (Finn)have ovulationrates of three to four, and the highly prolificHooroolaMerino ovulateson average five to six ova (l-4). Gonadotropichormoneconcentrations have been cunparedin breeds of sheep that vary in ovulationrate to determinewhether this genetictrait is expressedthroughalteredhormonal levelsand patterns. Recent studiesconcerningendocrinephysiologyof the HooroolaMerino have led to the conclusionthat increasedFSH secretiondoss contributeto the higher ovulationrate of this Merino strain. The HcoroolaMerino, canparedto the control Merino, has higher circulatingand urinaryFSH levels during the periovulatoryperiod (5). D'Man and Rarenovewes also have higher FSH levels than ewes of less prolificbreeds. D'Mans have higherFSH concentrationsduring the pariovulatoryperiod as ~11 as at certain other stages of the estrouscycle (2). Rmovs have higher FSH levels during the prelutealphase (6). A canparisonof FSH levels in Finn and less prolificsheep during the estrouscycle has not been reported. Experimentalevidencegained fran ovariectanized Finn and Suffolksheep indicatesthat an underlyingbreed differencein FSH secretionmay exist (7). On the other hand, similarFSH levelswere seen in intactFinn and Suffolk ewes followingprogesteroneimplantremoval (8). In our study,FSH levels in Finn, Suffolkand Targheeewes were cazparedto determine whetherFiMS conformto other prolificbreeds in having higher FSH levels at one time or anotherduring the estrous cycle.

Eighteen2- to 6-yr-oldporous ewes ware assignedrandanlywithin breed in equal.numbersto the study. Finn, Suffolkand Targheeewas were allottedfrcxnrespectiveflocks havingmaan + SlEMovulationrates of 3.09 + 0.13, 1.82 f 0.14 and 1.70 + 0.14 (4). Finn ewes weighed (Z 2 SD) 51.5 + 2.4 kg, Suffolks63.3 + 1.4 kg and Targhees64.7 + 6.3 kg. Sheep ware penned with vasect&zed marker rams and nmintgined under environmental photopericd(44'53'N). Hay and corn ware fed daily at 0800 h. In Novemberand December,marked ewes were checkedfor standing estrus at 0600, 1400 and 2200 h. A blood samplewas taken by venipunctureat time of detectionof standingestrus and thereafterat 8-h intervalsuntil standingestrus was detectedagain. The first day of standingestrus was termed Day 0, and on Day 10 endoscopicexamination was performadto record number of corporalutea and ovariansurface follicles23 mn in diameter. Animalswx-e sedatedwith acepranazine prior to endoscopy. One-wayanalysisof variancewas used to test differencesamong breeds in estrouscycle length and durationof preluteal,lutealand

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postlutealphases. Prelutealphase was the tin-eintervalfran onset of estrus to beginningof the lutealphase, the lutealphase was definedas the period in which plasma progesteronelevelswere 20.4 ng/ml, and the postlutealphase was the time fran the end of the luteal phase to onset of estrus. One-wayanalysisof variancewas also performedon other data where there was oneobservationper animal. Plasma IHandESHvalues during the estrouscycle ware examinedstatisticallyin a split-plot Breed and blocd samplingtine design for repeatedmeasures (9). were consideredmain and subplots,respectively. Individualrnaans were tested for significantdifferencesusing Duncan'snew multiple range test. Harologous,double-antibody radioimnunoassays were used to measure plasma LH and FSH levels (10,111. Antiserumand hormonalpreparationsfor radioicdination and referencein the LH assay ware GDN-15,LER-1056x2 and NM-IH-S19, respectively; and in the FSH assay corresponding materialsCnRreDJB-RS-4IA,NIWDD-oFSH-I-1and NIAMDD-oFSH-13.Assay sensitivities were 0.3 ng/ml LH and 3 ng/inl FSH. Duplicate100 ul plasnm aliquotswere assayedfor LH and all samplesware includedin one assay. The intra-assayccefficientof variation(CV) was 10%. Cne FSH radioinmuncassay was conductedin which duplicate300 ul plasma aliguotsware assayedand the intraassay CV was 11%. A notablemodificationto the ovine FSH radioimmunoassayproceduredescribedby Bolt (11)was that the radioiodination mixturewas chrcxnatcgraphed CBIa Sepharose 4B-Concanavalin A calm followingthe protocolof Chap@ (12). Progesteronewas measuredusing a solid phase radioismuncassay that had been previouslyvalidatedfor use with sheep plasma (13). Sensitivitywas 0.1 ng/ml and the intra-assayCV was 7%. Mean and standarderror are presentedin the text.

FlEsJLTs

Length of estrouscycleswere different(P
Ovulationrate of Finns (3.5+ 0.2) was greater (P
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THERIOGENOLOGY

10

1

FlNN

10

TARGHEE

HOUR AFTER LH SURGE Figure I. Plasrrka progesteroneconcentrations(X + SE?41during the estrouscycle. Time 0 correspondsto plasm sampleshaving highestKH levels,~typicall~ 9 to 17 h after onset of estrus. Blood samplesware taken at 8-h intervalsfran six Finn, Suffolkand Targheeewas.

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. Z,

Number of corporalutea was not relatedto peak progesterone area under the curve or durationof the lutealphase.

Plasma LH levels are also presented(Figure21. Ths interval fran onset of estrus to highestpreovulatoryLH surge level tended (P = 0.1) to be lonuer in Finns (17.3+ 3.4 h) than in Suffolks (9.3 + 2.7 h) and Targhees (9.3 + 2.7 h). -Adding these intervalsto thosG of the postlutealphase est&tes total time availablefor preovulatory folliculargrowth. This lengthof time varied (PCO.011among breed and was longer in Targees (40 + 2 h) than in Finns (30 f.3 hl and Suffolks (29 + 2 h). HighestpreovulatoryIH surge levelsdetected were lower (PO.l). Levels of LH-werehigher (P
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>lO

-I PARGHEE S-

0

-24

1*1‘,,.....,““.,*....,.**..,.....,*....,....*,.....,~

0 24

72

120

168

216

264

312

360

408

HOUR AFTER LH SURGE

Figure 2. Plasma Ii-I levelsduring the estrous cycle. At 0 h, Finn = 45 + 15, Suffolk= 108 + 31 and Targhee= 189 + 35 ng/ml.

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40-

6UFFOLK

? ol c 20i?

20-

during the estrouscycle. Figure 3. Plasma ESH ccncentrations At 0 h, Targee = 55 + 16 ng/ml.

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frcanRaMnovs,D'mans and_roolaMerinosin thatevlRsof these prolific breeds have higher ESH levelsat certainstages of the estrous cycle than ewes of nonprolificbreeds (2,6,14). Results at hand discountthe possibilitythat elevatedperiperalFSH concentrations contributeto the high ovulationrate of the Finn as they have been proposedto do in ths D'Man, Rarmnov and BooroolaMerino. A side-byside canparisonof FSH levels in ewes of these breeds is needed to revealwhether FSH concentrations actuallydo differ among them. Three to four secretoryepisodeswere discerniblein FSH profiles of most ewas. Periodicfluctuationsin RSH concentrations have been reportedby other investigators and have been presumedto reflect waves of folliculargrowth (15,16). Driancourtet al. (171,on the contrary,have suggestedthatfolliculargrowth occurs atrandanand that folliclescan enlargeunder a wide range of hormonallevels. They observedfolliclesof various size on the surfaceof the ovary regardlessof stage of the estrous cycle. We found no relationship betweennumber of visable follicles23 mn in diameterand FSH level on Day 10. The intervalfran onset of estrus to the preovulatoryLH surge tended to be longer in Finns than in Suffolksand Targhees. Excluding BcoroolaMerinos,longer intervalsare typical in ewes having high ovulationrates (14). Althoughlength of the intervalhas been correlated with ovulationrate, Cahill et al. (6) point out that the length of the intervalis not a determinantof ovulationrate becauseat the onset of estrus,ovulatoryfolliclesalreadyhave been selected. Preselectionof ovulatoryfolliclesprecludesa role of the preovulatory gonadotropinsurge in determinationof ovulationrate. This is supportedby resultsof Land et al. (18),who found ovulationrate to be independentof maxim~~~ LS concentration, and by our findingsthat the amplitudeof the LH dischargewas higher in Targees than in FiMS and Suffolks. The higher LR surge levels in Targheesmay have induced a greaterextent of pituitaryTdJdepletionandtorIdown-regulation and, in this manner, caused the lower I.&I concentrations seen in these ewes just after the surge. Targheesalso had more tine availablefor preovulatoryfolliculargro&h, which was estimatedby adding postluteal and estrus-to-LHsurge intervals. Thus, time availablefor preovulatoryfolliculargrowth does not appear to be an importantfactor in bringingabout a high ovulationrate. A portionof the preovulatorygonadotropinsurge was detectedin each ewa and a positiverelationshipexisted betweenLH and FSH surge levels. Atothertimes during the estrous cycle, plasma IHandE'SH patternsbore no resemblance. Hcx+?ver, wz did find suna evidencethat suggestsDH and FSH secretionare not entirelyindependent.When plasma 'U-l and ESH levelswere averagedwithin sheep,excludingpreovulatory gonadotropinsurge values, there was a strong relationshipbstween nraanLH and FSH levels. A ewe that had a high aean I-Hvalue also had a high mean FSH value and vice versa. &e possibilityin this regard is that there is a prcportionalsynthesisof gonadotrqins and size of pituitaryLH and ESH pools set the overall level of hormonal output. Anotherpossibilityis that E-land FSH output are tied to the number of gonadotrophs.Wan plasma LH and J?SHlevelsand L,Rto FSH ratios ware similar in Finn, Suffolkand Targheeewes.

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Similarityof systemicgonadotropinconcentrations points to intraovarian mechanismsas primary sites for genotypicregulationof ovulationrate. The size of folliclesat mturity is importantin determiningovulationrate, since the smallerthe follicleis at maturity,the greaterthe pool of potentialovulatoryfollicles(19). Early follicularmaturationseems to be a characteristic of Finn sheep. Webb and Gauld (20) found more antralestrcgenicfolliclesin Finn than Suffolkewes even though the follicleswere of similarsize. Ovulatoryfolliclesrange fran 4 to 6 mn in Finn ewas and from 7 to 8 mn in Suffolkewes. Mechanism elicitingearly sensitivityof folliclesto gonadotropinsappearsto be a likely site for genotypic regulationof ovulationrate.

1. Cahill,L.P., Mariana,J.C. and Mauleon,P. Total follicular populationsin ewes of high and low ovulationrates. J. Reprcd. Fertil.-55:27-36 (1979). A., Schams,D. and Glatzel,P. Plasma gonadotropin 2. Iahlou-Kassi, concentrations during the cestrouscycle and after ovariectcmyin two breeds of sheep with low and high fecundity. J. Reprcd. Fertil.70:X5-173 (1984). 3. Driancourt,M.A., Cahill,L.P. and Bindon,B.M. Ovarianfollicular populationsand preovulatoryenlargementin Boorcolaand controlMerino ewes. J. Reprcd. Fertil.-73:93-107(1985). 4. Youngs, C.R. GeneticVariationin OvulationRate, Litter Size and mryonic Loss in Sheep. Ph.D. Thesis. Universityof Minnesota,St. Paul, 1985. 5. Bindon, B.M., Piper, L.R., Cumnins,L.J., O'Shea,T., Hillard, M-A., Findlay,J.K. and Robertson,D.M. Reproductiveendocrinology of prolificsheep: studiesof the Boxoola Nerino. In: Iand, R.B. and Robinson,D.W. (eds.). Geneticsof Reprcdu&on in Sheep. Buttermrths, Lcodon,1985, pp. 217-235. 6. Cahill,L.P., Samande, ,J.,Ravault,J.P., Blanc,M., Thin-mier, J ., Mariana,J.C. and Mauleon,P. Hormonaland follicular relationshipsin ewes of high and low ovulationrates. J. Reprcd. Fertil.-62:141-150(1981). 7. Webb, R., Baxter,G., Preece,R.D., Land, R.B. and Springbett, A.J. Cmtrol of gonadotrophinreleasein ScottishBlackface and FinnishLandraceewes during seasonalanoestrus. J. Reprod. Fertil.-73:369-378(1985). of the ovulatory 8. Webb, R. and Eugland,B.G. Identification folliclein the ewe: Associatedchangesin follicularsize, thecal and granulosacell luteinizinghornme receptors, antral fluid steroids,and circulatinghormonesduring the preovulatoryperiod. Endocrinology -110:873-881(1982). 9. Gill, J.L. and Hafs, H.D. Analysisof repeatedmeasurementsof animals. J. Anim. Sci. 2:331-336 (1971).

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10.

Niswxder, G.D., Reichert,L.E., Jr., Midgley,A.R., Jr. and Nal!xmdov,A.V. Radioimnunoassay for bovine and ovine luteinizinghome. Endocrinology -84:1166-1173(1969).

for 11. Bolt, D.J. Eevelopnentof a hamlogous radioimnuncassay ovine folliclestimulatinghorn-me: Studiesafter estrus, ovariectcmy,estracliol and releasingtinnone. J. Anim. Sci. 53:730-741(1981). 12. Chappel,S.C. The presenceof two speciesof follicle-stimulating hornme within hamsteranteriorpituitaryglands as disclosedby 109:935-942(1981). CcncanavalinA chramtqraphy. Endocrinology 13. Hamra,Ad, Massri,Y.G., Marcek, J.M. and wheaton,J.E. Plasm progesteronelevels in ewes treatedwith progesteronecontrolledinternaldrug-releasedispensers,implantsand sponges. Anim. Reprcd. Sci. a:187-194 (1986). 14. Bindcn,B.M., Piper, L.R. and Thimmier, J. PreovulatoryLH characteristics and tine of ovulationin the prolificBcoroola Merino ewe. J. Reprod.Fertil.2:519-523 (1984). 15. Miller,K.F., Nordheim,E.V. and Ginther,O.J. Periodicfluctuationsin FSH concentrations during the ovine estrouscycle. Thericgenology x:669-679 (1981). 16. Bister,J.L. and Paquay, R. Fluctuationsin the plasma levels of the follicle-stimulating hormoneduring estrouscycle, anestrus,gestationand lactationin the ewe: Bvidenosfor an endcgenousrhythm of ESH release. Thericgenolcgy -19:565-582 (1983). 17. Driancourt,M.A., Gibson,W.R. and Cahill,L.P. Follicular dynamicsthroughoutthe cestruscycle in sheep. A review. Reprod.N&r. Develop.-25:1-15 (1985). 18. T&d, R-B., Pelletier,J., Thimonier,J. and Mauleon,P. A quantitativestudy of geneticdifferencesin the incidenceof oestrus,ovulationma plasm luteinizinghormoneconcentration in the sheep. J. Endoxinol. 8:305-317 (1973). 19. McNatty,K.P., Lun, S., Heath, D.A., Ball, K., Smith, P., Hudson, N-L., McDiarmid,J., Gibe, M. and Henderson,K.M. Differencesin ovarianactivitybetweenBmroola x Merino ewes which wsre hano_ zygous,heterozygousand non-carriersof a mjor gene influencing their ovulationrate. ,J.Repro& Fertil.z:193-205 (1986). 20. Webb, R. and Gaul& I.K. Folliculogenesis in sheep: Controlof ovulationrate. In: Land, R.B. ad Robinson,D.W. teds.). Geneticsof Reprc&ction in Sheep. Buttermxths, London, 1985, pp. 267-274.

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