- Email: [email protected]
Seasonally anovulatory ewes fail to respond to progestogen treatment in the absence of gonadotropin stimulation
Theriogenology
42: 1329-l
336, 1994
SEASONALLY ANOVULATORY EWES FAIL TO RESPOND TO PROGESTOGEN TREATMENT IN THE ABSENCE OF GONADOTROPIN STIMULATION S.H. Umberger, G. Jabbarl and G.S. Lewis Department of Animal and Poultry Sciences Virginia Polytechnic Institute and State University Blacksburg, VA 24061-0306 Received for publication: April 6, 1994 Accepted: October 20, 1994 ABSTRACT The induction of synchronized estrus for June-July breeding of ewes treated with melengestrol acetate (MGA) or Norgestomet implants (SMB) was evaluated in relation to the ram effect and treatment with PG-600 at the time of progestogen withdrawal. Anovulatory Dorset, Suffolk, and Hampshire ewes (n=140) were randomly assigned within breed groups to 1 of 5 treatments: 1) control; 2) MGA only (MGA); 3) MGA + PG-600 (PMGA); 4) SMB only (SMB); and 5) SMB + PG-600 @MB). Beginning June 15, MGA- and PMGA-treated ewes were fed 0.3 mg MGA/d in a mixture of shelled corn and a commercially prepared pelleted supplement containing MGA. Concomitantly, the SMB- and PSMB-treated ewes were given a 3-mg SMB implant inserted subcutaneously at the back of the ear. At the end of the 10-d treatment period, MGA supplementation was discontinued, the SMB implants were removed, and both the PMGA- and PSMB-treated ewes were given a single intramuscular injection of PG600 (400 IU PMSG + 200 IU hCG). One-half of the ewes in each treatment group were placed with fertile rams equipped with marking harnesses on June 24 for a 30-d breeding period, while the other ewes remained isolated t?om the rams. To monitor luteal activity of ewes exposed or not exposed to rams, blood samples for progesterone analysis were collected at 0,4, 7 and 10 d after termination of the progestogen treatments. At least 79% of all the ewes exposed to rams had luteal activity. In the absence of rams, only ewes treated with PG-600 had an increase (P < 0.0001) in luteal activity. Fertility for control and MGA- and SMB-treated ewes was not different, but the progestogen-treated ewes lambed an average of 12 d earlier in the lambing period than the control ewes. These data indicate that ram exposure or administration of an exogenous source of gonadotropin after progestogen withdrawal is necessary for the induction of ovulation and subsequent corpus luteum formation for the June-July breeding of anovulatory ewes. Key words:
melengestrol acetate, Norgestomet, anestrous ewes, PMSG, ram effect
Research was supported by the U&AID/University of Illinois TIPAN Project, NWFP, Pakistan. *Present address: Village and Post Office Ningolai, District Swat, NWFP, Pakistan.
Copyright
Q 1994 Butterworth-Heinemann
1330
Theriogenology
INTRODUCTION Progestogen treatment of seasonally anovular ewes is used to synchronize estrus for out-ofseason breeding (4). To promote the outward signs of estrus and cause a closer synchrony of ovulation, it is recommended that approximately 500 IU PMSG be given at the time of progestogen withdrawal (3). However, in studies that used natural mating, acceptable lambing rates and intervals from ram introduction to lambing were obtained without gonadotropin treatment (5, 14, 15). Seasonally anovulatory ewes previously isolated from rams exhibit estrus 18 to 25 d after ram introduction; a phenomenon referred to as the ram effect (8). Priming anovular ewes with progesterone before ram introduction advances the first estrus to within 5 d after ram exposure and eliminates premature luteal regression in ewes responding to the ram effect (11). The decreasing size of the sheep industry and the limited use of artificial insemination with sheep in the United States has resulted in a reluctance on the part of manufacturers of synthetic progestogens and suppliers of exogenous sources of gonadotropins for estrus synchronization to make the substantial investment required for product approval. Products commercially available for estrus synchronization with other species of livestock have been used for the control of reproduction in sheep. Melengestrol acetatea (MGA), administered orally for the suppression of estrus and ovulation in feedlot heifers, and Syncro-Mate-Bb (SMB), administered by subcutaneous ear implant for estrus synchronization in beef cattle, have been used for the control of estrus and ovulation in seasonally anovular ewes (l-2, 6, 12, 14). Until recently, sources of PMSG were limited. The introduction of PG-600C for the induction of e&us in prepuberal gilts provides a commercially available supply of PMSG. One S-n& dose of PG-600 contains 400 IU of PMSG and 200 IU of hCG. To evaluate the relationship of gonadotropin treatment and ram effect on progestogen-primed ewes in seasonal anestrus, a study was conducted measuring luteal activity (in the absence and presence of rams) and lambing performance of ewes treated with MGA and SMB with and without PG-600. MATERIALS AND METHODS Blood samples were collected from nonlactating, multiparous Dorset, Suffolk and Hampshire ewes (n=220) on June 4 and 9 by jugular venipuncture to assess estrual status via blood serum progesterone analysis. Ewes (n=80) with blood serum progesterone concentrations of 0.5 ng/mL or greater were considered cyclic and were not included in the study. The remaining ewes (n=I40) were characterized as being seasonally anovular and were randomly assigned within breed groups (50% Dorset and 50% blackfaced ewes) to 1 of 5 treatments (Table 1): 1) control; 2) 10 d MGA only (MGA; fed at 0.3 mg/ewe/d); 3) 10 d MGA + PG-600 (5 mL i.m.; PMGA); 4) 3 mg Norgestomet (Sycro-Mate-B) implanted for 10 d (SMB); and 5) 3 mg Norgestomet + PG-600 (5 mL i.m.; PSMB). Thus, this study was designed to include a negative aupjohn, I&WIZOO, MI, USA. bSanofi Animal Health, Overland Park, KS, USA. CIntervet, Millsboro, DE, USA.
Theriogenology control (Treatment 1) accompanied by a 2 x 2 factorial arrangement of treatments involving 2 progestogens with and without PG-600. Lambs had been weaned from ewes for 2 30 d, and were isolated from rams for 130 d before initiation of the study. Beginning 1 wk before treatment and throughout the 10-d treatment period, all the ewes were fed whole-shelled corn at the rate of 0.45 kg/ewe/d.
Table 1.
Treatment schedule
Day of treatment Treatment Control MGA only (MGA)b MGAIPG-600 (PMGA) SMB only (SMB)c SMB/PGdOO (PSMB) 14 a30-d breeding period with a 1: 18 ram to ewe ratio. b.3 mg of MGAlewelday. c3-mg Norgestomet implant. d5 mL of PG-600 (400 IU PMSG + 200 IU hCG).
-1oto-1 Corn Corn MGA MGA MGA MGA SMB SMB SMB SMB
oa
Injection of PGdOOdRam Injection of PG-60Od
Injection of PG-600d/Ram Injection of PG-60Od
Beginning on June 15, MGA- and PMGA-treated ewes were fed 0.45 kg of a 70:30 mixture of whole-shelled corn and a commercially prepared pelleted supplement (2.2 mg/kg of MGA) at the same time each morning. Concomitantly, SMB- and PSMB-treated ewes were given a 3-mg SMB implant (one-half of the cattle dosage) inserted subcutaneously at the back of the ear. At the end of the 10-d treatment period, MGA supplementation was discontinued, and the SMB implants were removed through a small incision made in the skin at the distal end of the implant. Concomitantly, PMGA- and PSMB-treated ewes were given a single intramuscular injection of PG-600 (5 mL). One-half of the ewes in each treatment group were placed with fertile rams on June 24 for a 30-d breeding period, while the other ewes remained isolated from rams. All rams were equipped with marking harnesses. Marker colors were changed on days 10 and 20 of the breeding period. Ewes were checked daily at 0900 h, and marking information was recorded. To monitor luteal activity of ewes exposed to or not exposed to rams, blood samples for progesterone analysis were collected by jugular venipuncture at 0, 4, 7 and 10 d after termination of the progestogen treatments. After collection, the blood samples were stored out of
1332
Theriogenology
direct sunlight and allowed to clot. Serum samples were collected and kept frozen until all samples could be assayed for progesterone concentration. Concentrations of progesterone were determined in 100 pl of serum, in duplicate, with the Coat-A-Counta radioimmunoassay. Samples were reevaluated if duplicate values differed by more than 25% and 0.1 ng/rnL. The intra- and inter-assay coefficients of variation were 5.2 and 11%, respectively. After breeding, the ewes were maintained under pasture conditions until approximately 4 wk before lambing, when grain supplementation was initiated. Individual ewe lambing information was collected on treatment groups with ram exposure. Lambing information was not considered for ewes with no exposure to rams during the study period. C&square analyses were conducted using the frequency procedure of SAS (13) to determine the effect of treatment on the categorical variables of mating, luteal activity and fertility. Analysis of variance was conducted using the GLM procedures of SAS to evaluate the fixed effect of treatment on lambing interval and prolificacy. Orthogonal contrasts for control vs treated ewes, and the factorial effects of progestogen, PG-600 administration, and their interactions were tested for all dependent variables using the CATMOD and GLM procedures of SAS. RESULTS Blood serum progesterone concentrations 2 0.5 ng/mL were used as an indicator of Following progestogen withdrawal, a large ovulation and corpus luteum (CL) formation. proportion of all ewes exposed to rams had increased progesterone concentrations within 10 d after ram introduction (Table 2). However, in the absence of rams, only ewes treated with PG-600 at the time of progestogen withdrawal had an increase (P < 0.0001) in luteal activity. A greater (P < 0.004) proportion of progestogen-treated ewes mated at the synchronized estrus (Table 3). Within progestogen treatments, rams marked more (P < 0.001) SMB- than MGA-treated ewes during the first 5 d of breeding. Except for the SMB treatment, repeat matings after the synchronized estrus were 2 20%. Fertility for controls and the MGA- and SMB-treated ewes was not different (Table 3). However, more (P < 0.04) Dorset than blackfaced ewes lambed (68 vs 43%) in all treatments. Progestogen-treated ewes lambed earlier (P < 0.001) in the lambing period than control ewes because the time of first mating was advanced at the synchronized estrus. Within progestogen treatments, prolificacy was increased (P < 0.03) by 0.50 lambs for the SMB-treated ewes.
aDiagnostic Products, Los Angeles, CA, USA.
1333
Theriogenology DISCUSSION
Luteal activity was greatest for ewes exposed to rams (2 79%) and for ewes treated with PG-600 at progestogen withdrawal (2 93%). The response for induction of ovulation and subsequent CL formation was low (5 21%) for ewes treated with progestogen only without ram exposure.
Table 2.
Dayc 0
4
Percentage of ewes showing first luteal activitya by blood sampling date, in the presence (+) or absence (-) of rams
+
Control 7 7
MGA 7 0
+
44
7
29 7
Treatmentn PMGA 21 0
SMB 0 0
PSMB 7 0
72 50
21 0
57 57
7
+
14 0
57 14
7 36
79 7
29 36
10
+
14 0
0 0
0 7
0 0
7 0
o- 10d
+
79f 93f 1OOf 14e 21e 93f aBlood serum progesterone concentration 2 0.5 ng/mL. bTreatment groups are defined in Table 1. cDays after progestogen withdrawal. dcumulative percentage of ewes showing luteal activity (c 0,4,7, e*fValues with different superscripts differ (P < 0.0001).
1OOf 7e
1OOf 93f
IO).
Sudden introduction of rams to seasonally anovular ewes, after 2 2 wk of isolation from rams, causes an increase in the frequency and amplitude of LH production within minutes after ram exposure, followed by ovulation approximately 50 h later (10). Typically, this ovulatory response is not accompanied by estrus and frequently results in premature luteal regression within 4 to 6 d after ram introduction, followed by a second e&us-free ovulation and CL with normal life spans (9). Subsequent ovulations are accompanied by behavioral e&us, thus yielding 2 peaks of breeding activity at 18 and 22 d after ram introduction (7). Luteal activity and mating records from this study reflect a response for control ewes that can be attributed to the ram effect. Seventy-nine percent of the control ewes exposed to rams had an increase in luteal activity within 10 d after ram introduction compared with only 14% of control ewes not
50 79 50.0 1.4ofg
25 86 64.3 1.33f
50 79 57.1 1.67fg
Repeat mating (%)d
Total ewes marked (%)
Lambing rate (%)
Lambs born per ewe lambing
1.908
50
86
20
71g
PSMB (+) 14
Days from ram 163.7 f 2.8f 154.6 f 2.88 152.8 f 3.78 148.8 f 3.48 151.2*2.618 introduction to lambinge aTreatment groups are defined in Table 1. bContrasts: 1 (Control vs MGA and SMB). 2 (MGA vs SMB). CSynchronized es&us through Day 5 for progestogen-treated ewes and through Day 17 for control ewes. dRepeat mating, % = ewes remarked/ewes marked at synchronized e&us. evalues represent least squares means f SEM. f,gValues in the same row with different superscripts differ (PcO.03). *p
1.83fg
50.0
93
8
93
43g
57g
14f
SMB (+) 14
Ewes marked at synchronized estrus (%)c
Item Number of ewes
MGA (+) 14
Treatmenta PMGA (+) 14
**
-
**
-
*
**
Contrastsb 1 2
Effect of treatment on e&us, fertility, prolificacy and interval from ram introduction to lambing for treatment groups with ram exposure
Control (+) 14
Table 3.
2 g
1335
Theriogenology
exposed to rams. Premature luteal regression, a common occurrence associated with the ram effect, was evident, with peaks of breeding activity at 17.3 and 23.2 d after ram introduction. Progestogen treatment of seasonally anovular ewes, advanced the onset of estrus to witbin 5 d after ram introduction and eliminated premature regression of the CL in ewes responding to the ram effect (11). In our study, 82% of the SMB-treated ewes and 50% of MGA-treated ewes were marked by rams within the first 5 d of the breeding period. More than 98% of the progestogen-treated ewes had increased serum progesterone concentmtions within 10 d after ram introduction, an indication that ovulation and subsequent CL formation had occurred as a result of the ram effect. The induction of synchronized estrus through progestogen treatment resulted in an average interval from ram introduction to lambing of 12 fewer days than obtained with the control ewes. These results are consistent with other studies in which MGA (12, 14) and SMB (6) were used to induce synchronized estrus in seasonally anovulatory ewes. They also support the unpublished results of a previous study in which intervals from ram introduction to lambing were shortest for SMB-treated ewes (152 d), intermediate for MGA-treated ewes (155 d), and longest for the control ewes (167 d). In both studies, a greater proportion of SMB-treated ewes were marked at synchronized estrus than MGA-treated ewes, but there was no difference in subsequent fertility for the MGA, SMB and the untreated control ewes. In the absence of rams, the mean incidence of luteal activity for control, MGA and SMB ewes after progestogen withdrawal was low (14%). Conversely, PMGA and PSMB ewes not exposed to rams had a frequency of luteal activity similar to that of ewes with rams. Consequently, progestogen treatment alone was inadequate for the induction of synchronized estrus in seasonally anovular ewes. Gonadotropin stimulation either through the introduction of a ram or through the administration of an exogenous source of gonadotropin after progestogen withdrawal was required for the induction of ovulation and subsequent CL formation. The ram effect was just as effective in stimulating luteal activity in progestogen-primed ewes as PG-600. Neither synchronized estrus nor fertility was improved through gonadotropin treatment. In conclusion, these findings indicate that progestogen-treatment of ewes for out-of-season breeding is ineffective without gonadotropin stimulation. Sudden introduction of a ram after progestogen withdrawal was as effective as exogenous treatment with PG-600. Progestogen treatment did not improve fertility, but it did shorten the interval from ram introduction to lambing. REFERENCES 1.
2. 3.
Alifakiotis T, Michailidis I, Gavrilidis G. Induced breeding in anestrous milking ewes of dairy breeds: comparison of norgestomet, medroxyprogesterone and flourogestone in two regimes of PMSG. Theriogenology 1982; 17:603-6 10. Carpenter RH, Spitzer JC. Response of anestrous ewes to norgestomet and PMSG. Theriogenology 1981;15:389-393. Gordon I. Induction of early breeding in sheep by standard and modified progestogen-PMS treatments. J Agric Sci 1971;76:337-341.
1336 4. 5.
6.
10.
11.
12. 13. 14. 15.
Theriogenology
Gordon I. Hormonal control of reproduction in sheep. Proc Br Sot Anim Prod 1975;4:7993. Hunter GL, Belonje PC, Van Niekerk CH. Synchronized mating and lambing in spring-bred Merino sheep: the use of progestogen-impregnated intravaginal sponges and teaser ram. Agroanimalia 1971;3:133-140. Jabbar G, Umberger SH, Lewis GS. A comparison of melengestrol acetate and norgestomet used alone or in combination with reran01 or PMSG and hCG for improved spring-breeding performance in auestrous ewes. J Anim Sci 1993;71 (Suppl. 1):242 abstr. Knight TW, Tervit HR, Fairclough RJ. Corpus luteum function in ewes stimulated by rams. Theriogenology 1981;15:183-190. Martin GB, Oldham CM, Cognie Y, Pearce DT. The physiological responses of anovulatory ewes to the introduction of rams - a review. Livest Prod Sci 1986;15:219-247. Oldham CM, Martin GB. Stimulation of seasonally anovular Merino ewes by rams. II. Premature regression of ram-induced corpora lutea. Anim Reprod Sci 1978; 1:291-295. Oldham CM, Martin GB, Knight TW. Stimulation of seasonally anovular Merino ewes by rams. I. Time from introduction of the rams to the preovulatory surge and ovulation. Anim Reprod Sci 1978;1:283-290. Pearce DT, Martin GB, Oldham CM. Corpora lutea with a short life-span induced by rams in seasonally anovulatory ewes are prevented by progesterone delaying the preovulatory surge of LH. J Reprod Fertil 1985;75:79-84. Safianski TJ, Lamberson WR, Keisler DH. Use of melengestrol acetate and gonadotropins to induce fertile estrus in seasonally anestrous ewes. J Anim Sci 1992;70:2935-2939. SAS. SAS/STAT User’s Guide, Version 6, Vol. 1. Cary, NC, 1990. Umberger SH, Lewis GS. Melengestrol acetate (MGA) for estrous synchronization and induction of estrus in spring-breeding ewes. Sheep Res J 1992;8:59-62. Wheaton JR, Windels HF, Johnston LJ. Aceeleramd lambing using exogenous progesterone and the ram effect. J Anim Sci 1992;70:2628-2635.
42: 1329-l
336, 1994
SEASONALLY ANOVULATORY EWES FAIL TO RESPOND TO PROGESTOGEN TREATMENT IN THE ABSENCE OF GONADOTROPIN STIMULATION S.H. Umberger, G. Jabbarl and G.S. Lewis Department of Animal and Poultry Sciences Virginia Polytechnic Institute and State University Blacksburg, VA 24061-0306 Received for publication: April 6, 1994 Accepted: October 20, 1994 ABSTRACT The induction of synchronized estrus for June-July breeding of ewes treated with melengestrol acetate (MGA) or Norgestomet implants (SMB) was evaluated in relation to the ram effect and treatment with PG-600 at the time of progestogen withdrawal. Anovulatory Dorset, Suffolk, and Hampshire ewes (n=140) were randomly assigned within breed groups to 1 of 5 treatments: 1) control; 2) MGA only (MGA); 3) MGA + PG-600 (PMGA); 4) SMB only (SMB); and 5) SMB + PG-600 @MB). Beginning June 15, MGA- and PMGA-treated ewes were fed 0.3 mg MGA/d in a mixture of shelled corn and a commercially prepared pelleted supplement containing MGA. Concomitantly, the SMB- and PSMB-treated ewes were given a 3-mg SMB implant inserted subcutaneously at the back of the ear. At the end of the 10-d treatment period, MGA supplementation was discontinued, the SMB implants were removed, and both the PMGA- and PSMB-treated ewes were given a single intramuscular injection of PG600 (400 IU PMSG + 200 IU hCG). One-half of the ewes in each treatment group were placed with fertile rams equipped with marking harnesses on June 24 for a 30-d breeding period, while the other ewes remained isolated t?om the rams. To monitor luteal activity of ewes exposed or not exposed to rams, blood samples for progesterone analysis were collected at 0,4, 7 and 10 d after termination of the progestogen treatments. At least 79% of all the ewes exposed to rams had luteal activity. In the absence of rams, only ewes treated with PG-600 had an increase (P < 0.0001) in luteal activity. Fertility for control and MGA- and SMB-treated ewes was not different, but the progestogen-treated ewes lambed an average of 12 d earlier in the lambing period than the control ewes. These data indicate that ram exposure or administration of an exogenous source of gonadotropin after progestogen withdrawal is necessary for the induction of ovulation and subsequent corpus luteum formation for the June-July breeding of anovulatory ewes. Key words:
melengestrol acetate, Norgestomet, anestrous ewes, PMSG, ram effect
Research was supported by the U&AID/University of Illinois TIPAN Project, NWFP, Pakistan. *Present address: Village and Post Office Ningolai, District Swat, NWFP, Pakistan.
Copyright
Q 1994 Butterworth-Heinemann
1330
Theriogenology
INTRODUCTION Progestogen treatment of seasonally anovular ewes is used to synchronize estrus for out-ofseason breeding (4). To promote the outward signs of estrus and cause a closer synchrony of ovulation, it is recommended that approximately 500 IU PMSG be given at the time of progestogen withdrawal (3). However, in studies that used natural mating, acceptable lambing rates and intervals from ram introduction to lambing were obtained without gonadotropin treatment (5, 14, 15). Seasonally anovulatory ewes previously isolated from rams exhibit estrus 18 to 25 d after ram introduction; a phenomenon referred to as the ram effect (8). Priming anovular ewes with progesterone before ram introduction advances the first estrus to within 5 d after ram exposure and eliminates premature luteal regression in ewes responding to the ram effect (11). The decreasing size of the sheep industry and the limited use of artificial insemination with sheep in the United States has resulted in a reluctance on the part of manufacturers of synthetic progestogens and suppliers of exogenous sources of gonadotropins for estrus synchronization to make the substantial investment required for product approval. Products commercially available for estrus synchronization with other species of livestock have been used for the control of reproduction in sheep. Melengestrol acetatea (MGA), administered orally for the suppression of estrus and ovulation in feedlot heifers, and Syncro-Mate-Bb (SMB), administered by subcutaneous ear implant for estrus synchronization in beef cattle, have been used for the control of estrus and ovulation in seasonally anovular ewes (l-2, 6, 12, 14). Until recently, sources of PMSG were limited. The introduction of PG-600C for the induction of e&us in prepuberal gilts provides a commercially available supply of PMSG. One S-n& dose of PG-600 contains 400 IU of PMSG and 200 IU of hCG. To evaluate the relationship of gonadotropin treatment and ram effect on progestogen-primed ewes in seasonal anestrus, a study was conducted measuring luteal activity (in the absence and presence of rams) and lambing performance of ewes treated with MGA and SMB with and without PG-600. MATERIALS AND METHODS Blood samples were collected from nonlactating, multiparous Dorset, Suffolk and Hampshire ewes (n=220) on June 4 and 9 by jugular venipuncture to assess estrual status via blood serum progesterone analysis. Ewes (n=80) with blood serum progesterone concentrations of 0.5 ng/mL or greater were considered cyclic and were not included in the study. The remaining ewes (n=I40) were characterized as being seasonally anovular and were randomly assigned within breed groups (50% Dorset and 50% blackfaced ewes) to 1 of 5 treatments (Table 1): 1) control; 2) 10 d MGA only (MGA; fed at 0.3 mg/ewe/d); 3) 10 d MGA + PG-600 (5 mL i.m.; PMGA); 4) 3 mg Norgestomet (Sycro-Mate-B) implanted for 10 d (SMB); and 5) 3 mg Norgestomet + PG-600 (5 mL i.m.; PSMB). Thus, this study was designed to include a negative aupjohn, I&WIZOO, MI, USA. bSanofi Animal Health, Overland Park, KS, USA. CIntervet, Millsboro, DE, USA.
Theriogenology control (Treatment 1) accompanied by a 2 x 2 factorial arrangement of treatments involving 2 progestogens with and without PG-600. Lambs had been weaned from ewes for 2 30 d, and were isolated from rams for 130 d before initiation of the study. Beginning 1 wk before treatment and throughout the 10-d treatment period, all the ewes were fed whole-shelled corn at the rate of 0.45 kg/ewe/d.
Table 1.
Treatment schedule
Day of treatment Treatment Control MGA only (MGA)b MGAIPG-600 (PMGA) SMB only (SMB)c SMB/PGdOO (PSMB) 14 a30-d breeding period with a 1: 18 ram to ewe ratio. b.3 mg of MGAlewelday. c3-mg Norgestomet implant. d5 mL of PG-600 (400 IU PMSG + 200 IU hCG).
-1oto-1 Corn Corn MGA MGA MGA MGA SMB SMB SMB SMB
oa
Injection of PGdOOdRam Injection of PG-60Od
Injection of PG-600d/Ram Injection of PG-60Od
Beginning on June 15, MGA- and PMGA-treated ewes were fed 0.45 kg of a 70:30 mixture of whole-shelled corn and a commercially prepared pelleted supplement (2.2 mg/kg of MGA) at the same time each morning. Concomitantly, SMB- and PSMB-treated ewes were given a 3-mg SMB implant (one-half of the cattle dosage) inserted subcutaneously at the back of the ear. At the end of the 10-d treatment period, MGA supplementation was discontinued, and the SMB implants were removed through a small incision made in the skin at the distal end of the implant. Concomitantly, PMGA- and PSMB-treated ewes were given a single intramuscular injection of PG-600 (5 mL). One-half of the ewes in each treatment group were placed with fertile rams on June 24 for a 30-d breeding period, while the other ewes remained isolated from rams. All rams were equipped with marking harnesses. Marker colors were changed on days 10 and 20 of the breeding period. Ewes were checked daily at 0900 h, and marking information was recorded. To monitor luteal activity of ewes exposed to or not exposed to rams, blood samples for progesterone analysis were collected by jugular venipuncture at 0, 4, 7 and 10 d after termination of the progestogen treatments. After collection, the blood samples were stored out of
1332
Theriogenology
direct sunlight and allowed to clot. Serum samples were collected and kept frozen until all samples could be assayed for progesterone concentration. Concentrations of progesterone were determined in 100 pl of serum, in duplicate, with the Coat-A-Counta radioimmunoassay. Samples were reevaluated if duplicate values differed by more than 25% and 0.1 ng/rnL. The intra- and inter-assay coefficients of variation were 5.2 and 11%, respectively. After breeding, the ewes were maintained under pasture conditions until approximately 4 wk before lambing, when grain supplementation was initiated. Individual ewe lambing information was collected on treatment groups with ram exposure. Lambing information was not considered for ewes with no exposure to rams during the study period. C&square analyses were conducted using the frequency procedure of SAS (13) to determine the effect of treatment on the categorical variables of mating, luteal activity and fertility. Analysis of variance was conducted using the GLM procedures of SAS to evaluate the fixed effect of treatment on lambing interval and prolificacy. Orthogonal contrasts for control vs treated ewes, and the factorial effects of progestogen, PG-600 administration, and their interactions were tested for all dependent variables using the CATMOD and GLM procedures of SAS. RESULTS Blood serum progesterone concentrations 2 0.5 ng/mL were used as an indicator of Following progestogen withdrawal, a large ovulation and corpus luteum (CL) formation. proportion of all ewes exposed to rams had increased progesterone concentrations within 10 d after ram introduction (Table 2). However, in the absence of rams, only ewes treated with PG-600 at the time of progestogen withdrawal had an increase (P < 0.0001) in luteal activity. A greater (P < 0.004) proportion of progestogen-treated ewes mated at the synchronized estrus (Table 3). Within progestogen treatments, rams marked more (P < 0.001) SMB- than MGA-treated ewes during the first 5 d of breeding. Except for the SMB treatment, repeat matings after the synchronized estrus were 2 20%. Fertility for controls and the MGA- and SMB-treated ewes was not different (Table 3). However, more (P < 0.04) Dorset than blackfaced ewes lambed (68 vs 43%) in all treatments. Progestogen-treated ewes lambed earlier (P < 0.001) in the lambing period than control ewes because the time of first mating was advanced at the synchronized estrus. Within progestogen treatments, prolificacy was increased (P < 0.03) by 0.50 lambs for the SMB-treated ewes.
aDiagnostic Products, Los Angeles, CA, USA.
1333
Theriogenology DISCUSSION
Luteal activity was greatest for ewes exposed to rams (2 79%) and for ewes treated with PG-600 at progestogen withdrawal (2 93%). The response for induction of ovulation and subsequent CL formation was low (5 21%) for ewes treated with progestogen only without ram exposure.
Table 2.
Dayc 0
4
Percentage of ewes showing first luteal activitya by blood sampling date, in the presence (+) or absence (-) of rams
+
Control 7 7
MGA 7 0
+
44
7
29 7
Treatmentn PMGA 21 0
SMB 0 0
PSMB 7 0
72 50
21 0
57 57
7
+
14 0
57 14
7 36
79 7
29 36
10
+
14 0
0 0
0 7
0 0
7 0
o- 10d
+
79f 93f 1OOf 14e 21e 93f aBlood serum progesterone concentration 2 0.5 ng/mL. bTreatment groups are defined in Table 1. cDays after progestogen withdrawal. dcumulative percentage of ewes showing luteal activity (c 0,4,7, e*fValues with different superscripts differ (P < 0.0001).
1OOf 7e
1OOf 93f
IO).
Sudden introduction of rams to seasonally anovular ewes, after 2 2 wk of isolation from rams, causes an increase in the frequency and amplitude of LH production within minutes after ram exposure, followed by ovulation approximately 50 h later (10). Typically, this ovulatory response is not accompanied by estrus and frequently results in premature luteal regression within 4 to 6 d after ram introduction, followed by a second e&us-free ovulation and CL with normal life spans (9). Subsequent ovulations are accompanied by behavioral e&us, thus yielding 2 peaks of breeding activity at 18 and 22 d after ram introduction (7). Luteal activity and mating records from this study reflect a response for control ewes that can be attributed to the ram effect. Seventy-nine percent of the control ewes exposed to rams had an increase in luteal activity within 10 d after ram introduction compared with only 14% of control ewes not
50 79 50.0 1.4ofg
25 86 64.3 1.33f
50 79 57.1 1.67fg
Repeat mating (%)d
Total ewes marked (%)
Lambing rate (%)
Lambs born per ewe lambing
1.908
50
86
20
71g
PSMB (+) 14
Days from ram 163.7 f 2.8f 154.6 f 2.88 152.8 f 3.78 148.8 f 3.48 151.2*2.618 introduction to lambinge aTreatment groups are defined in Table 1. bContrasts: 1 (Control vs MGA and SMB). 2 (MGA vs SMB). CSynchronized es&us through Day 5 for progestogen-treated ewes and through Day 17 for control ewes. dRepeat mating, % = ewes remarked/ewes marked at synchronized e&us. evalues represent least squares means f SEM. f,gValues in the same row with different superscripts differ (PcO.03). *p
1.83fg
50.0
93
8
93
43g
57g
14f
SMB (+) 14
Ewes marked at synchronized estrus (%)c
Item Number of ewes
MGA (+) 14
Treatmenta PMGA (+) 14
**
-
**
-
*
**
Contrastsb 1 2
Effect of treatment on e&us, fertility, prolificacy and interval from ram introduction to lambing for treatment groups with ram exposure
Control (+) 14
Table 3.
2 g
1335
Theriogenology
exposed to rams. Premature luteal regression, a common occurrence associated with the ram effect, was evident, with peaks of breeding activity at 17.3 and 23.2 d after ram introduction. Progestogen treatment of seasonally anovular ewes, advanced the onset of estrus to witbin 5 d after ram introduction and eliminated premature regression of the CL in ewes responding to the ram effect (11). In our study, 82% of the SMB-treated ewes and 50% of MGA-treated ewes were marked by rams within the first 5 d of the breeding period. More than 98% of the progestogen-treated ewes had increased serum progesterone concentmtions within 10 d after ram introduction, an indication that ovulation and subsequent CL formation had occurred as a result of the ram effect. The induction of synchronized estrus through progestogen treatment resulted in an average interval from ram introduction to lambing of 12 fewer days than obtained with the control ewes. These results are consistent with other studies in which MGA (12, 14) and SMB (6) were used to induce synchronized estrus in seasonally anovulatory ewes. They also support the unpublished results of a previous study in which intervals from ram introduction to lambing were shortest for SMB-treated ewes (152 d), intermediate for MGA-treated ewes (155 d), and longest for the control ewes (167 d). In both studies, a greater proportion of SMB-treated ewes were marked at synchronized estrus than MGA-treated ewes, but there was no difference in subsequent fertility for the MGA, SMB and the untreated control ewes. In the absence of rams, the mean incidence of luteal activity for control, MGA and SMB ewes after progestogen withdrawal was low (14%). Conversely, PMGA and PSMB ewes not exposed to rams had a frequency of luteal activity similar to that of ewes with rams. Consequently, progestogen treatment alone was inadequate for the induction of synchronized estrus in seasonally anovular ewes. Gonadotropin stimulation either through the introduction of a ram or through the administration of an exogenous source of gonadotropin after progestogen withdrawal was required for the induction of ovulation and subsequent CL formation. The ram effect was just as effective in stimulating luteal activity in progestogen-primed ewes as PG-600. Neither synchronized estrus nor fertility was improved through gonadotropin treatment. In conclusion, these findings indicate that progestogen-treatment of ewes for out-of-season breeding is ineffective without gonadotropin stimulation. Sudden introduction of a ram after progestogen withdrawal was as effective as exogenous treatment with PG-600. Progestogen treatment did not improve fertility, but it did shorten the interval from ram introduction to lambing. REFERENCES 1.
2. 3.
Alifakiotis T, Michailidis I, Gavrilidis G. Induced breeding in anestrous milking ewes of dairy breeds: comparison of norgestomet, medroxyprogesterone and flourogestone in two regimes of PMSG. Theriogenology 1982; 17:603-6 10. Carpenter RH, Spitzer JC. Response of anestrous ewes to norgestomet and PMSG. Theriogenology 1981;15:389-393. Gordon I. Induction of early breeding in sheep by standard and modified progestogen-PMS treatments. J Agric Sci 1971;76:337-341.
1336 4. 5.
6.
10.
11.
12. 13. 14. 15.
Theriogenology
Gordon I. Hormonal control of reproduction in sheep. Proc Br Sot Anim Prod 1975;4:7993. Hunter GL, Belonje PC, Van Niekerk CH. Synchronized mating and lambing in spring-bred Merino sheep: the use of progestogen-impregnated intravaginal sponges and teaser ram. Agroanimalia 1971;3:133-140. Jabbar G, Umberger SH, Lewis GS. A comparison of melengestrol acetate and norgestomet used alone or in combination with reran01 or PMSG and hCG for improved spring-breeding performance in auestrous ewes. J Anim Sci 1993;71 (Suppl. 1):242 abstr. Knight TW, Tervit HR, Fairclough RJ. Corpus luteum function in ewes stimulated by rams. Theriogenology 1981;15:183-190. Martin GB, Oldham CM, Cognie Y, Pearce DT. The physiological responses of anovulatory ewes to the introduction of rams - a review. Livest Prod Sci 1986;15:219-247. Oldham CM, Martin GB. Stimulation of seasonally anovular Merino ewes by rams. II. Premature regression of ram-induced corpora lutea. Anim Reprod Sci 1978; 1:291-295. Oldham CM, Martin GB, Knight TW. Stimulation of seasonally anovular Merino ewes by rams. I. Time from introduction of the rams to the preovulatory surge and ovulation. Anim Reprod Sci 1978;1:283-290. Pearce DT, Martin GB, Oldham CM. Corpora lutea with a short life-span induced by rams in seasonally anovulatory ewes are prevented by progesterone delaying the preovulatory surge of LH. J Reprod Fertil 1985;75:79-84. Safianski TJ, Lamberson WR, Keisler DH. Use of melengestrol acetate and gonadotropins to induce fertile estrus in seasonally anestrous ewes. J Anim Sci 1992;70:2935-2939. SAS. SAS/STAT User’s Guide, Version 6, Vol. 1. Cary, NC, 1990. Umberger SH, Lewis GS. Melengestrol acetate (MGA) for estrous synchronization and induction of estrus in spring-breeding ewes. Sheep Res J 1992;8:59-62. Wheaton JR, Windels HF, Johnston LJ. Aceeleramd lambing using exogenous progesterone and the ram effect. J Anim Sci 1992;70:2628-2635.