Boshoff, D.A.

Morgenthal, J.C.

van Niekerk, C.H.

English

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TiME OF OVULA nON IN THE KARAKUL EWE FOLLOWING SYNCHRONIZA nONOF OESTRUSDie mvloed van medroksi-progesteroonasetaat geiinpregneerde intravaginale sponse en dragtige merrie serum gonadotroCien (DMSGIop die lengte van die estrusperiode. die tyd vanaf sponsonttrekking tot die begin van estrus. die tyd van ovulasie en dIe aantal ovulasies isondersoek. Die proef is binne en buite die teelseisoen met gusooie sowel as post partum-ooie gedoen. DMSG het nie die lengte van die estrus-periode beiJlvloed nie. maar het wel die tyd vanaf sponsonttrekking tot die begin van estrus verkort. die tyd van ovulasie, bepaal vanaf spons-onltrekking en die begin van estrus, vervroeg en die aantal ovulasies per ooi vermeerder. Volgens die resultate wat verkry is. word kUllsmatigeinseminasie 36, 48 en 60 uur na sponsonttrekking aanbeveel. sonder om die begin van estrus met koggelramme vas te stet. Dieselfde tye vaninseminasie geld vir gU5- en post partum ooie. ongeag watter stadium van die teelseisoen sinkronisasie toegepas word.The mfluence of medroxyproge,terone acetate impregnated intravaginal sponges and pregnant mare serum (PMSG) on the length ofoestrus. thl length of the interval from sponge withdrawal to the beginning of oestrus. the length of the interval from the beginning ofoestrus to ovulat ion and the number of ovulations per ewe was investigated. Barren and post partum ewes were used during both the breed-ing and nOli-breeding seasons. PMSG had no effect on the length of oestrus. but shortened the period from sponge withdrawal to the begin-ning of oestrus. advanced the time of ovulation in relation to both the beginning of oestrus and sponge withdrawal, and inl-1"eased the numberof ovulatiors per ewe. The time interval from sponge withdrawal to the beginning of oestrus was found to be shorter, and the length of oestruslonger in the normal breeding as compared to the non-breeding season. The number of ovulations per ewe. and the interval from sponge with-drawal to ovulation were not subject to seasonal influences: and no differences were apparent between barren and post partum ewes.Without thl' predetermination of the beginning of oestrus by teaser rams. artificial insemination at 36, 48 and 60 hr after sponge with-drawal is recommended irrespective of the season during which synchronization is applied.In th~ ewe ovulation occurs towards the end of oestrus.Few cases are known where this happens, under naturalconditions, within 24 hours of the beginning of oestrus(Anderson, 1938). Information concerning the time ofovulation I'ollowing synchronization of oestrus in the ewewith progesterone impregnated sponges and pregnant mareserum gonadotrophin is limited. Van Niekerk & Belonje(1970) fomd that Merino ewes ovulate from 70 to 90hours after the removal of intravaginal sponges impregnatedwith medroxyprogesterone acetate (MAP, Upjohn). How-ever wher~ fluorogestone acetate impregnated sponges(FGA, G.D. Searly & Co.) were employed in Dormer ewes,ovulation took place as early as 45 to 80 hours after spongewithdrawal, or two and a half hours after the end of oestrus(Van der Westhuizen, Van Niekerk & Hunter, 1970).The purpose of the present study was to determinethe time 0 r' ovulation in Karakul ewes after treatment withmedroxyplOgesterone acetate impregnated intravaginalsponges (Rl~promap Plus, Upjohn) and pregnant mare serum*Present address: Agricultural Research Station, P.O. Box 37,Upington.gonadotrophin in order to establish the critical time forartificial insemination following sponge withdrawal. Appli-cation of this information could then be used to excludethe need to use teaser rams for oestrus detection p"jorto artificial insemination.Both barren and post partum Karakul ewes wereused within as well as outside the normal breedingseason (which lasts from the second half of January to thefirst half of August) to determine (a) the period from spongewithdrawal to the beginning of oestrus, (b) the length ofthe oestrus period, (c) the time of ovulation and thetotal number of ovulations per ewe. In the case of theparturient ewes the lambs were removed within 24 hoursof birth, allowing the uterus to be fully involuted by the28th. day post partum (Van Wyk, Van Niekerk & Belonje,1972), when the sponges were inserted. The allocation ofexperimental animals into the various groups is given inTable 1.As a precaution against vaginal infection each animalSeasonIBreeding Non-breedingNo. of ewesI48 48Reproductive status Barren I Post-partum~Barren Post PartumimNo. of ewes 24 24 oL"o 24 24I.U. PMSG* 750 500 250 0 500 250 500 250 0 750 500 250 0No. of ewes 6 6 6 6 I 6 6 6 6 1 6 6 6 6 6 6 6 6received two ml of a five per cent (w/v) dehydrostrepto-mycin solution (Agavin, May & Baker) intravaginally,after which sponges impregnated with 40 mg medroxy-progesterone acetate (Repromap Plus, Upjohn) were in-serted into the vagina of each ewe and left in situ for13 days. Thirty two hours before sponge withdrawal,pregnant mare serum gonadotrophin (PMSG, Upjohn)was administered intramuscularly at the following dosages:Group 1: 750 International UnitsGroup 2: 500 International UnitsGroup 3: 250 International UnitsGroup 4: Controls.Following sponge withdrawal the ewes were joinedby teaser rams and kept under constant observation foroestrus. On exhibiting oestrus, each ewe was removedfrom the rams and during the breeding season, laparotom-ized twenty hours afterwards for visual examination of theovaries. The laparotomies were repeated thereafter atfive-hourly intervals until such time as ovulation occurred.In the part of the experiment which took place in the non-breeding season, each of the ewes concerned was laparotom-ized 25 hours after the observed commencement of oestrusas indicated by the teaser rams. The end of oestrus wasdetermined in the ewes by observing their response toteaser rams which were rejoined with the ewes at 24hours after the beginning of oestrus, and at two-hourlyintervals thereafter until all the ewes had ceased to ex-hibit oestrus. The total number of ovulations per ewe wasdetermined by laparotomy of each ewe eight days afterthe end of oestrus, when the total number of corporalutea on the ovaries of each ewe was recorded.Results and discussionI. Interval from sponge withdrawal to beginning of .oestrus (Table 2)Fig. I. - The relationship between the dosage PMS and theinterval from sponge withdrawal to the beginningof oestrus.shortened the interval between sponge withdrawal and thebeginning of oestrus. Furthermore, there was a highly sig-nificant (P < 0,01) linear as well as quadratic relationshipbetween dosage of PMSG administered and the intervalfrom sponge withdrawal to the beginning of oestrus(Fig. 1). The quadratic relationship indicates that thisinterval is not always directly proportional to an increaseAverage period (hr.) from sponge withdrawal tobeginning of oestrusLV. !)MSG Breeding season Non-breedingseason° 48.9 72,1250 33,8 43,851)0 27.1 33.6750 25.1 27,4in PMSG levels; it will not be shortened by merely in-creasing tbe PMSG dosage. In accordance with the resultsof Holst (1969), the interval from sponge withdrawal tothe beginning of oestrus was found to be significantlyshorter within the breeding season than without (Table 2).The average length of oestrus induced during thenon-breedi!lg season (29,0 ± 0,56 hr) was highly significant-ly shorter (P < 0,01) than among ewes treated within thebreeding season (35,58 ± 0,56 hr) which is in accord-ance with the observations of Lamond (I 962) and Lamond& Bindon (I962). PMSG at the levels used in this study,did not influence the length of oestrus, and no notabledifferences were observed in this respect between barrenand post partum ewes.3. The interval from the beginning of oestrus toovuwtion (Table 3)The time of ovulation relative to the beginning ofoestrus was highly significantly (P < 0,0 I) and linearlyshortened by PMSG in both barren and post partum ewes,between which no notable difference could be detected.However, seasonal influences were important as exemplifiedby the fact that ovulation occurred significantly earlierin both barren and post partum ewes during the non-breeding season again without differences between thetwo groups. In addition a highly significant (P < 0,01)interaction occurred between breeding season on the onehand and the reproductive status of the ewes, (barren andpost partum) on the other.4. The interval between sponge withdrawal and ovuw-tion (Table 3)PMSG highly significantly (P < 0,0 I) decreased thetime from sponge withdrawal to ovulation, and a highlysignificant (P < 0,0 I), linear as well as quadratic relation-ship was found to occur between the level of PMSGadministered and the time of ovulation (Fig. 2). Incontrast to the seasonal effect on the interval betweenthe beginning of oestrus and ovulation as describedabove, it was noted that the time between sponge with-drawal and ovulation did not differ within or without thebreeding season. In view of the lack of any perceptibledifference between barren and post partum ewes, theresults of the two groups were combined, and from this itis evident that the groups to which 0; 250; 500 and 750LV. PMSG were administered respectively ovulated on theaverage 96,69; 71,88; 59,73 and 51,63 hours after spongewithdrawal.I Time of ovulation (hr.)I IAfter beginning of oestrus After sponge withdrawalLV. PMSG* 750 500 250 0 750 500 250 0During breeding B I 23.3 30.0 32,5 38.3 46.8 56.3 62,8 88.1season P 31.7 25,8 38.3 40.0 I 58,3 63,8 75,4 87.8During ne'n- B 23.3 26,7 33,3 34.8 50.5 60,0 79.8 95,4breeding ,;easonP 23.3 25,0 28.3 32.5 50.9 58.0 69.5 115.5*Internation,il Vnits of Pregnant Mare Serum GonadotrophinB = Barren ewesP = Post par' urn ewes.~.Fig. 2. - The time of ovulation in hours after sponge with-drawalThe total number of ovulations per ewe was directlyrelated to the dosage levels of PMSG administered. In the 0;250; 500 and 750 I.V. PMSG groups the average number ofovulations per ewe were respectively. 1.12; 1.44; 2,66and 4.88; this relationship between dosage of PMSG andovulations per ewe was found to be linear and highlysignificant (P < 0,01) and it was not influenced by seasonor by the reproductive status of the ewe. Fifty five per centof ovulations occurred on the right ovary as against 45 %on the left.Since laparotomies were not continued from whenthe first ovulations had been recorded until the establish-ment of the total number of ovulations per ewe (i.e.eight days later) the period during which multi-ovulationshad occurred is not known. However. it is possible tostate that this could not have been much longer than the12hr. described by Kil\een & Moore (1966), for the numberof ovulations per ewe recorded at the first ins tance did notvary much from the number of corpora lutea round in eachewe eight days later. In the 750 I.V. PMSG-groups it wasfound for example that the total number of ,'orpora luteabetween the two laparotomies were 108 and 117 respect-ively.Triplets are undesirable in the Karakul industry inview of the smaller, less valuable pelts prodl ced by suchlambs. In this study the average number of i)vulations ingroups having received 250 I.V. PMSG was found to be1,44; and it would seem highly unlikely that this couldhave resulted in significant numbers of multiple births.Even a dosage of 500 I.V. PMSG, which resulted in anaverage of 2,66 ovulations per ewe, should not have pro-duced too many twins if the observations of Van Rensburg(1964)- who indicated that the loss of ova could be ofthe order of 47 % - are taken into account. The possibilitythat triplets would ensue from the treatmi:nt at thesedosages. is thus very small and even the number of twinsshould not pose any particular problem.While environmental factors could pahaps exertan influence, it is evident from this study that the numberof ovulations per ewe is not affected by se,sonal differ-ences. Therefore. the same dosages of PMSG could be usedirrespective of whether synchronisation is applied withinthe breeding season or not. During the breeding season itwould be advisable - at least in the Karakul - to ad-minister PMSG at a shorter time prior to sponge withdrawalthan at other times of the year thereby, according to Hulet& Foote (1967), averting multi-ovulations. It would not beadvisable for this purpose to decrease the dosage of PMSGas this would tend to decrease the efficiency 0 f' synchroniz-ation.6. The application of artificial insemination of synchron-ized ewes without the use of teaser ram:; for the pre-determination of oestrusThe respective groups of ewes which'eceived 500I.V. PMSG ovulated between 45 and 75 hr. after spongewithdrawal during the non-breeding season. and between45 and 80 hr. in the breeding season. Therefore, threeinseminations at 12 hourly intervals beginning 36 hr.after sponge withdrawal should be sufficient irrespectiveof the season. Teaser rams may be useful at the thirdinsemination. when only those ewes still in oestrus areinseminated. Although such a recommendatic n should bepracticable under farming conditions. further investigationsare required in order to decrease the numbeJ of insemin-ations from three to two.ANDERSON, J., 1938. Ovulation in the ewe. J. agric. Sci.. Camb. 28, 64.HOLST, P.J., 1969. The ovarian response to pregnant mare serum (PMS) administered after intravaginal proge~togen treat-ment of cyclic and anoestrous ewes. Aust. J. agric. Res. 20, 1143.HVLET, C.V. & FOOTE. w.e .. 1967. Physiological factors affecting frequently and rate of lambing. J. animo Sci. 26, 553.KILLEEN, 1.0. & MOORE. N.W., 1970. The effect of Pregnant Mare Serum Gonadotrophin and fertility in the ewe.Aust. J. agric. Res. 21, 807.LAMOND, D.R., 1962. Effect of season on hormonally induced ovulation in Merino ewes. J. Reprod. Ferr. 4, Ill.LAMOND, D.R. & BINDON, BM., 1962. Oestrus, ovulation and fertility following suppression of ovarian cycles in Merinoew{~sby progesterone.J. Reprod. Fert. 4. 57.VAN DER WESTHUYSEN, 1M., VAN NIEKERK, C.H. & HUNTER, G.L., 1970. Time of ovulation and possible applica-tion of artificial insemination in sheep on a time basis after the use of progesterone sponges. Proc. S. Afr. Soc. Anim.Prod. 9, 183.VAN NIEKERK, ClI. & BELONJE, P .C., 1970. The time of ovulation after synchronization of oestrus in Merino ewes, withmedroxy-progesterone acetate. Proc. S. Afr. Soc. Anim. Prod. 9, 177.VAN RE\lSBURG, SJ., 1954. Ovum production: Action of various gonadotrophins in sheep and goats. Onderstepoort J. vet.Res. 31, 97.VAN WYK, L.C., VAN NIEKERK, C.H. & BELONJE, P.C., 1972. Involution of the post partum uterus of the ewe. JIS. Afr. vet. Ass. 43, 19.

Time of ovulation in the Karakul ewe following synchronization of oestrus

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Time of ovulation in the Karakul ewe following synchronization of oestrus

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