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Estrus induction following PGF2α treatment in the superovulated buffalo (Bubalus bubalis)
Theriogenology 59 (2003) 1203±1207
Estrus induction following PGF2a treatment in the superovulated buffalo (Bubalus bubalis) A.K. Misra*, H.C. Pant Sabarmati Ashram Gaushala, Lali 387 120, Kaira, Gujarat, India Received 25 July 2001; accepted 22 May 2002
Abstract Early return-to-estrus after embryo collection would shorten the interval between consecutive superovulations and improve ef®ciency of embryo production. Following superovulation and embryo collection, 80 buffaloes were treated with 15.0 mg Luprostiol (PGF2a analogue) for the induction of luteolysis and early return-to-estrus. A total of 67.5% donor animals returned to estrus, on average 11:8 0:84 days after the PGF2a treatment. The number of ovulations (5 or >5 CL) had no signi®cant effect on the percentage of donors returning to estrus within 30 days, as 70% of the buffaloes with 5 CL and 65% with >5 CL returned to estrus during this time. However, an increase in the number of ovulations signi®cantly delayed the return to estrus as this duration was 9:7 0:93 days in the buffaloes with 5 CL compared to 14:1 1:29 days in those having >5 CL. # 2002 Elsevier Science Inc. All rights reserved. Keywords: Buffalo; Superovulation; Embryo collection; Luteolysis; Estrus
1. Introduction Superovulation is the key step for embryo production. The number of repeated superovulations that can be performed on a donor buffalo in a given time depends on rapid return to normal estrous cycle after embryo collection. Also, if a buffalo is to become pregnant soon after embryo collection, a prerequisite for this would be rapid normalization of her estrus cyclicity. Prostaglandin F2 alpha or its analogues (PG) have been used extensively for estrus induction following embryo collection in cattle [1±9]. An average of 60±65% of superovulated cows exhibited estrus within 10 d after PG treatment [4,7]. However, similar * Corresponding author. Present address: Department of Animal Reproduction, Gynaecology and Obstetrics, College of Veterinary Sciences, G.B. Pant University of Agriculture and Technology, Pantnagar 263 145, Udham Singh Nagar, Uttaranchal, India. Tel.: 91-5944-33067; fax: 91-5944-33473. E-mail address: [email protected] (A.K. Misra).
0093-691X/02/$ ± see front matter # 2002 Elsevier Science Inc. All rights reserved. PII: S 0 0 9 3 - 6 9 1 X ( 0 2 ) 0 1 1 6 7 - 6
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A.K. Misra, H.C. Pant / Theriogenology 59 (2003) 1203±1207
reports are scanty in buffalo. Except for our earlier reports on 24 Surti [10] and 35 Murrah [11] buffaloes, and a contradictory report on 18 Surti buffaloes [12], we are not aware of any other reports of return-to-estrus interval following PG treatment in superovulated buffaloes. Therefore, the objective of this study was to substantiate our earlier observations of the return-to-estrus interval following PG treatment using a larger number (n 80) of superovulated buffaloes. 2. Materials and methods Eighty parous, cyclic Murrah-type buffaloes aged 6±7 years and weighing between 450 and 550 kg were used as donors. All animals were maintained under hygienic and optimum management conditions. This experiment was conducted in the winter season (ambient temperature: 18±24 8C) which is also the normal breeding season for the buffalo. All the buffaloes were treated with 600 mg NIH-FSH-P1(Folltropin, Vetrepharm, London, Ontario, Canada) to induce superovulation. After examination per rectum on Day 5.5±6 to count the number of ovulations (CL), embryos were collected nonsurgically using standard methods [13]. Immediately after embryo collection donors were treated with 15 mg Luprostiol (Prosolvin, Intervet, Holland) i.m. to avoid potential pregnancies of uncollected embryo(s), if any, and to expedite return-to-estrus. These buffaloes were observed for estrus for up to 30 days after Luprostiol treatment. Estrus was detected routinely with two vasectomized bulls (at 06:00, 14:00 and 22:00 h daily) and other behavioral signs such as mucus discharge from vulva, frequent micturition, swollen and edematous vulva, bellowing, and so forth. Data expressed as means were compared with the student's t-test while percentages were compared by Chi-square test [14]. 3. Results Half (n 40) of the buffaloes (50.0%) had 5 CL and the remaining 40 (50%) had >5 CL at time of embryo collection (Table 1). Table 1 Interval of return to estrus in superovulated buffalo cows following PGF2a treatment (15 mg Luprostiol i.m.) on the day of embryo collection Number of ovulations (CL)
Animals, n Buffalo cows in estrus within 30 days, n (%) Buffalo cows in standing estrus, n (%) Buffalo cows in non-standing estrus, n (%) Mean interval (days) to return to estrus (mean S.E.)
5
>5
40 28 (70.0) 27 (96.4) 1 (3.6) 9.7 0.93
40 26 (65.0) 26 (100.0) ± 14.1 1.29
Total
80 54 (67.5) 53 (98.1) 1 (1.9) 11.8 0.84
A.K. Misra, H.C. Pant / Theriogenology 59 (2003) 1203±1207
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Consequent to Luprostiol treatment, 67.5% donors returned to estrus within 11:8 0:84 days. The number of ovulations (5 or >5) had no signi®cant effect on the percentage of donors returning to estrus within 30 days, as 70% of the buffaloes with 5 CL and 65% with >5 CL returned to estrus during this time. Except for one animal with 5 CL which was observed in non-standing estrus, all the remaining donors (53) exhibited standing estrus. The increase in the number of ovulations signi®cantly (t 2:81, P < 0:01) delayed the return to estrus as this duration was 14:1 1:29 days in the buffaloes with >5 CL compared to 9:7 0:93 days in those having 5 CL. 4. Discussion Overall 67.5% of buffaloes responded to PGF2a treatment and returned to estrus within 30 days. The return to estrus interval was not affected by the number of ovulations, i.e. 5 (70.0%) or >5 (65.0%). These results are in agreement with our earlier report in which 68% of buffaloes responded to treatment with 15 mg Luprostiol on Days 8±15 after superovulatory estrus, or 69% responded to 15 mg Luprostiol treatment administered twice at an interval of 12 h (on Days 6±10 after superestrus). Current results are, however, lower than the 80, 94 and 100% responses found following treatment with 30, 15 (7.5 mg each at an interval of 12 h) and 22.5 mg Luprostiol, respectively, on Days 6 to 10 after superestrus [11]. Our results are also similar to those found in superovulated cattle treated with 500 mg Cloprostenol on day 7 or 8 where a 60% return to estrus rate was achieved [7]. Mean days to return to estrus in our study (11:8 0:84) were signi®cantly less than the 23:39 3:99 days reported earlier [12], but are in agreement with 10:0 5:83 days reported following treatment with 30 mg Luprostiol (15 mg administered twice, at an interval of 12 h). Current ®ndings are greater than the 5:47 2:59 to 8:13 3:52 days reported after treatment with 15 mg (7.5 mg administered twice, at an interval of 12 h) and 30 mg (one administration) Luprostiol on Days 6±10, respectively [11]. These results are also in agreement with our earlier report [10] in which 15 mg Luprostiol treatment between 5 and 8 days after superovulatory estrus induced estrus after 253:23 43:96 h (10.6 days) in buffaloes having 3 or more CL. Similar studies in cattle have also reported a mean interval of 9:7 1:52 days after a single treatment with Fenprostalene [9]; 10:5 1:1, 10:9 1:1 and 18:7 4:0 days after treatment with Cloprostenol, Fenprostalene and Dinoprost tromethamene, respectively [8,9]. It is apparent from our results that in the superovulated buffaloes the mean interval to estrus following PGF2a treatment was considerably prolonged (by about 12 days) compared to cyclic buffaloes in which estrus is synchronized with PGF2a within 3±4 days [15,16]. It is reasonable to suggest that this delay may be attributable to an elevated concentration of circulating progesterone due to multiple CL. The consequent negative feedback effect of progesterone on luteinizing hormone secretion may have attenuated follicular growth, as reported in cattle [2,9,17]. This conclusion is supported by our observation that, as in several studies in cattle [9,18,19] and buffalo [10,11], the return to estrus interval in superovulated buffaloes increased signi®cantly with an increase in the number of CL. A higher dose of PGF2a or repeated treatments with the recommended luteolytic dose may be of interest if the delay in estrus response is linked to higher levels of circulating
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progesterone secreted by the increased number of CL. In superovulated cattle a prolonged interval from PG treatment to estrus occurs when follicular development does not take place and an antagonistic relationship between CL and the follicle appears to exist [17]. Others have reported secretion of inhibin by the CL of sheep [20], rats [21] and humans [22]. If buffalo CL also secretes inhibin then higher amounts of inhibin from the multiple CL of superovulated buffaloes may also lead to suppression of follicular development. Further investigations are warranted to test these suggestions. Acknowledgements Financial assistance from the Department of Biotechnology, Govt. of India under the National Science and Technology Project on Embryo Transfer, is gratefully acknowledged. References [1] Greve T, Lehn-Jensen H. Fertility of high yielding dairy cows following superovulation and nonsurgical recovery of embryos. Theriogenology 1978;9:353±62. [2] Greve T. Bovine egg transplantation in Denmark. Carl Fr. Mortensen A/S Copenhagen, 1981. [3] Drost M. In: Roberts SJ, editor. Veterinary obstetrics and genital diseases, Theriogenology. Ann Arbor, MI: Edwards Brothers, Inc.; 1986, p. 927±41. [4] Chupin D, Touze JL, Procurer R. Early rebreeding of donor cows. Theriogenology 1984;21:231 [abstract]. [5] Boland MP, MacDonell HF, Ahmed TS, Reid JFS. Use of Fenprostalene in superovulated beef heifers. Vet Rec 1986;119:241±2. [6] Jones AL, Staples TR, Page RD. Enhanced return to estrus in superovulated heifers using fenprostalene. Theriogenology 1986;25:161 [abstract]. [7] Ali Dinar M, Diskin M, McDonagh T, Sreenan JM. Estrous and ovarian responses in repeatedly superovulated cows. Theriogenology 1987;27:201 [abstract]. [8] Halbert GW, Leslie KE, Walton JS, Betteridge KJ. Evaluation of return to estrus in superovulated dairy heifers following prostaglandin treatment. Theriogenology 1989;31:201 [abstract]. [9] Desaulniers DM, Guay P, Vaillancourt D. Estrus induction with prostaglandin F2a, Cloprostenol or Fenprostalene during the normal estrous cycle, superovulation and after embryos recovery. Theriogenology 1990;34:667±83. [10] Yadav MC, Misra AK, Motwani KT, Rajeshwaran S, Joshi BV. Ef®cacy of Luprostiol for inducing estrus in superovulated buffaloes. In: Proceedings of II World Buffalo Congress, vol. II. New Delhi, India; 1988, p. 128 [abstract]. [11] Rajeshwaran S, Trivedi KR, Misra AK, Joshi BV. Post superovulatory return to estrus with prostaglandin in buffalo (Bubalus bubalis). Indian Vet J 1993;70:131±3. [12] Sarvaiya NP, Chauhan FS, Mehta VM. Induction of oestrus in normal cyclic Surti buffaloes, during superovulation and after embryo recovery. Indian J Anim Sci 1993;63:1240±3. [13] Misra AK, Mutha Rao M, Kasiraj R, Rangareddy NS, Pant HC. Bull speci®c effect on fertilization rate and viable embryo recovery in the superovulated buffalo (Bubalus bubalis). Theriogenology 1999;52: 701±7. [14] Steel RGD, Torrie JH. Principles and procedures of statistics. New York: McGraw Hill; 1960. [15] Bachalus NK, Arora RC, Prasad A, Pandey RS. Effect of prostaglandin F2a tham salt and Estrumate (ICI 80996) on plasma progesterone levels in Indian water buffaloes (Bulabus bubalis). Theriogenology 1980;13:297±302. [16] Rao AR, Rao SV. Synchronization of oestrus in buffaloes with cloprostenol. Vet Rec 1978;103:288.
A.K. Misra, H.C. Pant / Theriogenology 59 (2003) 1203±1207
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[17] Lucy MC, Macmillan KL, Thatcher WW, Drost M, Tan HS. Effect of timing of prostaglandin PGF2a injection subsequent to embryo collection on the resumption of normal follicular development following superovulatory treatment in cattle. Theriogenology 1990;34:7±19. [18] Critser JK, Rowe RF, Del Campo MR, Ginther OJ. Embryo transfer in cattle: factors affecting superovulatory response, number of transferable embryos and length of post-treatment estrous cycle. Theriogenology 1980;13:397±406. [19] Mapletoft RJ, Bo GA, Willmott N, Pierson RA. The effect of dose of cloprostenol on return to estrus of superovulated donor cows. Theriogenology 1991;35:237 [abstract]. [20] Tsonis CG, McNeilly AS, Baird DT. Inhibin secretion by the sheep ovary during the luteal and follicular phases of the oestrous cycle and following stimulation with FSH. Endocrinol 1988;117:283±91. [21] Davis SR, Dench F, Nokolaidis I, Clements JA, Forage RG, Krozowski Z, et al. Inhibin A-subunit gene expression in the ovaries of immature female rats is stimulated by pregnant mare serum gonadotrophin. Biochem Biophys Res Comm 1986;138:1191±5. [22] Tsonis CG, Mesinis IE, Templeton AA, McNeilly AS, Baird DT. Gonadotropic stimulation of inhibin secretion by the human ovary during the follicular and early luteal phase of the cycle. J Clin Endocr Metab 1988;66:915±21.
Estrus induction following PGF2a treatment in the superovulated buffalo (Bubalus bubalis) A.K. Misra*, H.C. Pant Sabarmati Ashram Gaushala, Lali 387 120, Kaira, Gujarat, India Received 25 July 2001; accepted 22 May 2002
Abstract Early return-to-estrus after embryo collection would shorten the interval between consecutive superovulations and improve ef®ciency of embryo production. Following superovulation and embryo collection, 80 buffaloes were treated with 15.0 mg Luprostiol (PGF2a analogue) for the induction of luteolysis and early return-to-estrus. A total of 67.5% donor animals returned to estrus, on average 11:8 0:84 days after the PGF2a treatment. The number of ovulations (5 or >5 CL) had no signi®cant effect on the percentage of donors returning to estrus within 30 days, as 70% of the buffaloes with 5 CL and 65% with >5 CL returned to estrus during this time. However, an increase in the number of ovulations signi®cantly delayed the return to estrus as this duration was 9:7 0:93 days in the buffaloes with 5 CL compared to 14:1 1:29 days in those having >5 CL. # 2002 Elsevier Science Inc. All rights reserved. Keywords: Buffalo; Superovulation; Embryo collection; Luteolysis; Estrus
1. Introduction Superovulation is the key step for embryo production. The number of repeated superovulations that can be performed on a donor buffalo in a given time depends on rapid return to normal estrous cycle after embryo collection. Also, if a buffalo is to become pregnant soon after embryo collection, a prerequisite for this would be rapid normalization of her estrus cyclicity. Prostaglandin F2 alpha or its analogues (PG) have been used extensively for estrus induction following embryo collection in cattle [1±9]. An average of 60±65% of superovulated cows exhibited estrus within 10 d after PG treatment [4,7]. However, similar * Corresponding author. Present address: Department of Animal Reproduction, Gynaecology and Obstetrics, College of Veterinary Sciences, G.B. Pant University of Agriculture and Technology, Pantnagar 263 145, Udham Singh Nagar, Uttaranchal, India. Tel.: 91-5944-33067; fax: 91-5944-33473. E-mail address: [email protected] (A.K. Misra).
0093-691X/02/$ ± see front matter # 2002 Elsevier Science Inc. All rights reserved. PII: S 0 0 9 3 - 6 9 1 X ( 0 2 ) 0 1 1 6 7 - 6
1204
A.K. Misra, H.C. Pant / Theriogenology 59 (2003) 1203±1207
reports are scanty in buffalo. Except for our earlier reports on 24 Surti [10] and 35 Murrah [11] buffaloes, and a contradictory report on 18 Surti buffaloes [12], we are not aware of any other reports of return-to-estrus interval following PG treatment in superovulated buffaloes. Therefore, the objective of this study was to substantiate our earlier observations of the return-to-estrus interval following PG treatment using a larger number (n 80) of superovulated buffaloes. 2. Materials and methods Eighty parous, cyclic Murrah-type buffaloes aged 6±7 years and weighing between 450 and 550 kg were used as donors. All animals were maintained under hygienic and optimum management conditions. This experiment was conducted in the winter season (ambient temperature: 18±24 8C) which is also the normal breeding season for the buffalo. All the buffaloes were treated with 600 mg NIH-FSH-P1(Folltropin, Vetrepharm, London, Ontario, Canada) to induce superovulation. After examination per rectum on Day 5.5±6 to count the number of ovulations (CL), embryos were collected nonsurgically using standard methods [13]. Immediately after embryo collection donors were treated with 15 mg Luprostiol (Prosolvin, Intervet, Holland) i.m. to avoid potential pregnancies of uncollected embryo(s), if any, and to expedite return-to-estrus. These buffaloes were observed for estrus for up to 30 days after Luprostiol treatment. Estrus was detected routinely with two vasectomized bulls (at 06:00, 14:00 and 22:00 h daily) and other behavioral signs such as mucus discharge from vulva, frequent micturition, swollen and edematous vulva, bellowing, and so forth. Data expressed as means were compared with the student's t-test while percentages were compared by Chi-square test [14]. 3. Results Half (n 40) of the buffaloes (50.0%) had 5 CL and the remaining 40 (50%) had >5 CL at time of embryo collection (Table 1). Table 1 Interval of return to estrus in superovulated buffalo cows following PGF2a treatment (15 mg Luprostiol i.m.) on the day of embryo collection Number of ovulations (CL)
Animals, n Buffalo cows in estrus within 30 days, n (%) Buffalo cows in standing estrus, n (%) Buffalo cows in non-standing estrus, n (%) Mean interval (days) to return to estrus (mean S.E.)
5
>5
40 28 (70.0) 27 (96.4) 1 (3.6) 9.7 0.93
40 26 (65.0) 26 (100.0) ± 14.1 1.29
Total
80 54 (67.5) 53 (98.1) 1 (1.9) 11.8 0.84
A.K. Misra, H.C. Pant / Theriogenology 59 (2003) 1203±1207
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Consequent to Luprostiol treatment, 67.5% donors returned to estrus within 11:8 0:84 days. The number of ovulations (5 or >5) had no signi®cant effect on the percentage of donors returning to estrus within 30 days, as 70% of the buffaloes with 5 CL and 65% with >5 CL returned to estrus during this time. Except for one animal with 5 CL which was observed in non-standing estrus, all the remaining donors (53) exhibited standing estrus. The increase in the number of ovulations signi®cantly (t 2:81, P < 0:01) delayed the return to estrus as this duration was 14:1 1:29 days in the buffaloes with >5 CL compared to 9:7 0:93 days in those having 5 CL. 4. Discussion Overall 67.5% of buffaloes responded to PGF2a treatment and returned to estrus within 30 days. The return to estrus interval was not affected by the number of ovulations, i.e. 5 (70.0%) or >5 (65.0%). These results are in agreement with our earlier report in which 68% of buffaloes responded to treatment with 15 mg Luprostiol on Days 8±15 after superovulatory estrus, or 69% responded to 15 mg Luprostiol treatment administered twice at an interval of 12 h (on Days 6±10 after superestrus). Current results are, however, lower than the 80, 94 and 100% responses found following treatment with 30, 15 (7.5 mg each at an interval of 12 h) and 22.5 mg Luprostiol, respectively, on Days 6 to 10 after superestrus [11]. Our results are also similar to those found in superovulated cattle treated with 500 mg Cloprostenol on day 7 or 8 where a 60% return to estrus rate was achieved [7]. Mean days to return to estrus in our study (11:8 0:84) were signi®cantly less than the 23:39 3:99 days reported earlier [12], but are in agreement with 10:0 5:83 days reported following treatment with 30 mg Luprostiol (15 mg administered twice, at an interval of 12 h). Current ®ndings are greater than the 5:47 2:59 to 8:13 3:52 days reported after treatment with 15 mg (7.5 mg administered twice, at an interval of 12 h) and 30 mg (one administration) Luprostiol on Days 6±10, respectively [11]. These results are also in agreement with our earlier report [10] in which 15 mg Luprostiol treatment between 5 and 8 days after superovulatory estrus induced estrus after 253:23 43:96 h (10.6 days) in buffaloes having 3 or more CL. Similar studies in cattle have also reported a mean interval of 9:7 1:52 days after a single treatment with Fenprostalene [9]; 10:5 1:1, 10:9 1:1 and 18:7 4:0 days after treatment with Cloprostenol, Fenprostalene and Dinoprost tromethamene, respectively [8,9]. It is apparent from our results that in the superovulated buffaloes the mean interval to estrus following PGF2a treatment was considerably prolonged (by about 12 days) compared to cyclic buffaloes in which estrus is synchronized with PGF2a within 3±4 days [15,16]. It is reasonable to suggest that this delay may be attributable to an elevated concentration of circulating progesterone due to multiple CL. The consequent negative feedback effect of progesterone on luteinizing hormone secretion may have attenuated follicular growth, as reported in cattle [2,9,17]. This conclusion is supported by our observation that, as in several studies in cattle [9,18,19] and buffalo [10,11], the return to estrus interval in superovulated buffaloes increased signi®cantly with an increase in the number of CL. A higher dose of PGF2a or repeated treatments with the recommended luteolytic dose may be of interest if the delay in estrus response is linked to higher levels of circulating
1206
A.K. Misra, H.C. Pant / Theriogenology 59 (2003) 1203±1207
progesterone secreted by the increased number of CL. In superovulated cattle a prolonged interval from PG treatment to estrus occurs when follicular development does not take place and an antagonistic relationship between CL and the follicle appears to exist [17]. Others have reported secretion of inhibin by the CL of sheep [20], rats [21] and humans [22]. If buffalo CL also secretes inhibin then higher amounts of inhibin from the multiple CL of superovulated buffaloes may also lead to suppression of follicular development. Further investigations are warranted to test these suggestions. Acknowledgements Financial assistance from the Department of Biotechnology, Govt. of India under the National Science and Technology Project on Embryo Transfer, is gratefully acknowledged. References [1] Greve T, Lehn-Jensen H. Fertility of high yielding dairy cows following superovulation and nonsurgical recovery of embryos. Theriogenology 1978;9:353±62. [2] Greve T. Bovine egg transplantation in Denmark. Carl Fr. Mortensen A/S Copenhagen, 1981. [3] Drost M. In: Roberts SJ, editor. Veterinary obstetrics and genital diseases, Theriogenology. Ann Arbor, MI: Edwards Brothers, Inc.; 1986, p. 927±41. [4] Chupin D, Touze JL, Procurer R. Early rebreeding of donor cows. Theriogenology 1984;21:231 [abstract]. [5] Boland MP, MacDonell HF, Ahmed TS, Reid JFS. Use of Fenprostalene in superovulated beef heifers. Vet Rec 1986;119:241±2. [6] Jones AL, Staples TR, Page RD. Enhanced return to estrus in superovulated heifers using fenprostalene. Theriogenology 1986;25:161 [abstract]. [7] Ali Dinar M, Diskin M, McDonagh T, Sreenan JM. Estrous and ovarian responses in repeatedly superovulated cows. Theriogenology 1987;27:201 [abstract]. [8] Halbert GW, Leslie KE, Walton JS, Betteridge KJ. Evaluation of return to estrus in superovulated dairy heifers following prostaglandin treatment. Theriogenology 1989;31:201 [abstract]. [9] Desaulniers DM, Guay P, Vaillancourt D. Estrus induction with prostaglandin F2a, Cloprostenol or Fenprostalene during the normal estrous cycle, superovulation and after embryos recovery. Theriogenology 1990;34:667±83. [10] Yadav MC, Misra AK, Motwani KT, Rajeshwaran S, Joshi BV. Ef®cacy of Luprostiol for inducing estrus in superovulated buffaloes. In: Proceedings of II World Buffalo Congress, vol. II. New Delhi, India; 1988, p. 128 [abstract]. [11] Rajeshwaran S, Trivedi KR, Misra AK, Joshi BV. Post superovulatory return to estrus with prostaglandin in buffalo (Bubalus bubalis). Indian Vet J 1993;70:131±3. [12] Sarvaiya NP, Chauhan FS, Mehta VM. Induction of oestrus in normal cyclic Surti buffaloes, during superovulation and after embryo recovery. Indian J Anim Sci 1993;63:1240±3. [13] Misra AK, Mutha Rao M, Kasiraj R, Rangareddy NS, Pant HC. Bull speci®c effect on fertilization rate and viable embryo recovery in the superovulated buffalo (Bubalus bubalis). Theriogenology 1999;52: 701±7. [14] Steel RGD, Torrie JH. Principles and procedures of statistics. New York: McGraw Hill; 1960. [15] Bachalus NK, Arora RC, Prasad A, Pandey RS. Effect of prostaglandin F2a tham salt and Estrumate (ICI 80996) on plasma progesterone levels in Indian water buffaloes (Bulabus bubalis). Theriogenology 1980;13:297±302. [16] Rao AR, Rao SV. Synchronization of oestrus in buffaloes with cloprostenol. Vet Rec 1978;103:288.
A.K. Misra, H.C. Pant / Theriogenology 59 (2003) 1203±1207
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[17] Lucy MC, Macmillan KL, Thatcher WW, Drost M, Tan HS. Effect of timing of prostaglandin PGF2a injection subsequent to embryo collection on the resumption of normal follicular development following superovulatory treatment in cattle. Theriogenology 1990;34:7±19. [18] Critser JK, Rowe RF, Del Campo MR, Ginther OJ. Embryo transfer in cattle: factors affecting superovulatory response, number of transferable embryos and length of post-treatment estrous cycle. Theriogenology 1980;13:397±406. [19] Mapletoft RJ, Bo GA, Willmott N, Pierson RA. The effect of dose of cloprostenol on return to estrus of superovulated donor cows. Theriogenology 1991;35:237 [abstract]. [20] Tsonis CG, McNeilly AS, Baird DT. Inhibin secretion by the sheep ovary during the luteal and follicular phases of the oestrous cycle and following stimulation with FSH. Endocrinol 1988;117:283±91. [21] Davis SR, Dench F, Nokolaidis I, Clements JA, Forage RG, Krozowski Z, et al. Inhibin A-subunit gene expression in the ovaries of immature female rats is stimulated by pregnant mare serum gonadotrophin. Biochem Biophys Res Comm 1986;138:1191±5. [22] Tsonis CG, Mesinis IE, Templeton AA, McNeilly AS, Baird DT. Gonadotropic stimulation of inhibin secretion by the human ovary during the follicular and early luteal phase of the cycle. J Clin Endocr Metab 1988;66:915±21.