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Synchronization of estrus in virgin beef heifers using melengestrol acetate and PGF2α: an efficacy comparison of cloprostenol and dinoprost tromethamine
Theriogenology 57 (2002) 853±858
Synchronization of estrus in virgin beef heifers using melengestrol acetate and PGF2a: an ef®cacy comparison of cloprostenol and dinoprost tromethamine R.R. Salverson, J.M. DeJarnette*, C.E. Marshall, R.A. Wallace Select Sires Inc., 11740 U.S. 42, Plain City, OH 43064, USA Received 23 February 2001; accepted 30 April 2001
Abstract This study compared the ef®cacy of two sources of PGF2a on the reproductive performance of virgin beef heifers, after synchronization of estrus using melengestrol acetate (MGA) and PGF2a. Angus-based heifers (n 1002) in ®ve herds were fed 0.5 mg per head per day of MGA for 14 days. Nineteen days after the last day of MGA feeding, heifers were randomly assigned to receive (i.m.) either 0.5 mg cloprostenol (n 504; Estrumate1, E) or 25 mg dinoprost tromethamine (n 498; Lutalyse1, L) as a source of exogenous PGF2a. Heifers were observed twice daily for 5 days for signs of estrus and arti®cially inseminated 8±12 h later, except in herd A, wherein animals not detected in estrus by 80 h after PGF2a were mass-mated and no longer monitored for signs of estrus. Estrumate and Lutalyse were equally (P > 0:1) effective among all response variables evaluated, including estrus response (E, 89% and L, 86%), conception rate (E, 67% and L, 67%), and synchronized pregnancy rate (E, 61% and L, 57%). Synchrony of estrus was not affected (P > 0:1) by PGF2a source, and peak estrus response occurred 60 h post-PGF for both treatments. Conception rate to timed insemination was not different (P > 0:1) among Estrumate- and Lutalyse-treated heifers within herd A (14%, 4/28 and 7%, 2/29, respectively). Herd had a signi®cant (P < 0:05) effect on all indicators of reproductive performance. Conception rates within herds A and D were in¯uenced by technician (P < 0:05), however, this effect was balanced across treatments and no treatment by technician interaction was detected. In conclusion, when administered 19 days after a 14-day MGA feeding period, cloprostenol and dinoprost tromethamine are equally ef®cacious for synchronous induction of a fertile estrus in virgin beef heifers. # 2002 Elsevier Science Inc. All rights reserved. Keywords: PGF2a; Cloprostenol; Dinoprost tromethamine; Estrus synchronization; Melengestrol acetate
* Corresponding author. Tel.: 1-614-8734683; fax: 1-614-8735751. E-mail address: [email protected] (J.M. DeJarnette).
0093-691X/02/$ ± see front matter # 2002 Elsevier Science Inc. All rights reserved. PII: S 0 0 9 3 - 6 9 1 X ( 0 1 ) 0 0 6 9 2 - 6
854
R.R. Salverson et al. / Theriogenology 57 (2002) 853±858
1. Introduction The ability of exogenous PGF2a to regress the corpus luteum present on the ovary of cycling females [1,2] and the subsequent induction of a fertile estrus within 3±5 days [3±5] has facilitated its use in estrus synchronization programs. However, the ability of PGF2a to induce luteal regression is in¯uenced by the stage of the estrous cycle at the time of injection. Early-cycle animals (days 5±9) are less responsive to PGF2a than late-cycle animals (days 13±17) while mid-cycle (days 10±12) animals are intermediate in response [6±8]. Based on these results, Brown et al. [9] developed a synchronization program that includes a 14-day feeding period of melengestrol acetate (MGA), followed with an injection of PGF2a 17 days later. The MGA feeding period can induce cyclicity in some peripubertal heifers and pre-synchronizes corpus luteum development in cyclic animals. Further research with this protocol found a 19-day interval between MGA feeding and PGF2a injection to be slightly more ef®cacious due to the previously described stagedependent responsiveness of the corpus luteum [10]. In most countries, cloprostenol and dinoprost tromethamine are readily available sources of PGF2a; however, limited research has been conducted comparing the ef®cacy of these products [11,12]. Although, limited results indicate the two products are of comparable ef®cacy, no research has compared these products in conjunction with MGA-feedinginduced pre-synchronization of luteal development. The objective of this study was to compare the effects of cloprostenol and dinoprost tromethamine on the reproductive performance of virgin beef heifers synchronized to estrus using MGA and PGF2a. 2. Materials and methods Angus and Angus-based crossbred beef heifers (n 1002) in ®ve herds were fed a grain carrier containing 0.5 mg per head per day of MGA for 14 days. The animals were randomly assigned to receive (i.m.) either 0.5 mg cloprostenol (Estrumate1, Bayer Animal Health, Shawnee Mission, KS; n 504) or 25 mg dinoprost tromethamine (Lutalyse1, Pharmacia Animal Health, Kalamazoo, MI; n 498) 19 days after the last day of MGA feeding as exogenous sources of PGF2a. Four locations observed animals twice daily for signs of estrus for 5 days following the PGF2a injection and bred the heifers by AI 8±12 h after estrus was detected. In herd A, animals were observed and inseminated as previously described until 80 h after the PGF2a, at which time non-responding heifers were ®xed-time inseminated (TAI). Heifers were not exposed to herd bulls for at least 10 days following the last AI. Pregnancy diagnosis was determined via rectal palpation in herd E and by transrectal ultrasonography in all other herds, 30±60 days following a breeding season not exceeding 60 days in length. Data were analyzed using logistic regression and Chi-square procedures. Dependent variables were evaluated in full factorial logistic regression models that included the main effects of herd and treatment (Estrumate or Lutalyse). Due to the shortened estrus detection period, data from herd A (n 292) were not included in analyses of synchrony of estrus. Conception rates per AI were analyzed in the previously described model, with the addition of nested effects of sire within herd and technician with herd. In the absence of signi®cant
Table 1 Within- and across-herd effects of treatment on estrus response, conception, and pregnancy rates Herd
Treatmenta
Detected in estrus (%, number)
Conception rate Standing estrus (%, number)
TAI (%, number) 14 (4/28) 7 (2/29)
Synchronized pregnancy rate (%, number)
A
Estrumate Lutalyse
81 (119/147) 80 (116/145)
67 (80/119) 72 (83/116)
B
Estrumate Lutalyse
97 (87/90) 95 (86/91)
55 (48/87) 46 (40/86)
± ±
53 (48/90) 44 (40/91)
C
Estrumate Lutalyse
90 (46/51) 80 (36/45)
43 (20/46) 50 (18/36)
± ±
39 (20/51) 40 (18/45)
Dc
Estrumate Lutalyse
88 (92/104) 89 (96/108)
85 (77/91) 77 (72/94)
± ±
74 (77/103) 68 (72/106)
Ec
Estrumate Lutalyse
92 (103/112) 86 (94/109)
74 (74/100) 75 (69/92)
± ±
68 (74/109) 64 (69/107)
Totalc
Estrumate Lutalyse
89 (447/504) 86 (428/498)
67 (299/443) 67 (282/424)
a
14 (4/28) 7 (2/29)
57 (84/147) 59 (85/145)
61 (303/500) 57 (284/494)
All heifers received melengestrol acetate (0.5 mg per head per day) for 14 days and an injection (i.m.) of either Estrumate or Lutalyse 19 days after the last day of MGA feeding. b Heifers in herd A that were not detected in estrus by 80 h after prostaglandin treatment were fixed-timed inseminated (TAI). c Discrepancies in n values are due to heifers that were culled, sold, or died subsequent to synchronization of estrus, but prior to pregnancy diagnosis.
R.R. Salverson et al. / Theriogenology 57 (2002) 853±858
b
855
856
R.R. Salverson et al. / Theriogenology 57 (2002) 853±858
Fig. 1. Effects of Estrumate or Lutalyse on the synchrony of estrus in virgin beef heifers. Heifers were fed melengestrol acetate (0.5 mg per head per day) for 14 days followed with an injection (i.m.) of either cloprostenol (0.5 mg; Estrumate) or dinoprost tromethamine (25 mg; Lutalyse) 19 days later. Heifers were observed twice daily for signs of estrus and those not detected in estrus were considered non-responders (NR).
interactions, main effects were evaluated using Chi-square procedures. All statistical analyses were performed using SAS JMP1 Statistical Discovery Software, Version 4.0.2 (SAS Inst., Cary, NC). 3. Results Prostaglandin source had no effect (P > 0:1), within or across herds, on the measures of reproductive performance evaluated in this study. Estrus response was similar (P > 0:1) between treatments (Estrumate, 89% versus Lutalyse, 86%; Table 1), and peak estrus response occurred on an average of 60 h after the PGF2a injection in both treatments (Fig. 1). Irrespective of treatment, herd had a signi®cant effect (P < 0:05) on all indicators of reproductive performance. Conception rates within herds A and D were affected (P < 0:05) by technician; however, this effect was balanced across treatments, and no treatment by technician interaction was detected. Conception rate to timed insemination in herd A did not differ (P > 0:1) between treatments (Estrumate, 14% and Lutalyse, 7%). 4. Discussion Lutalyse and Estrumate demonstrated comparable ef®cacy for synchronous induction of a fertile estrus when administered 19 days following the 14-day period of MGA feeding. However, herd was found to in¯uence all indicators of reproductive performance evaluated. These results are similar to those of Seguin et al. [12], wherein reproductive performance of Holstein dairy cows was similar, following an injection of either Estrumate or
R.R. Salverson et al. / Theriogenology 57 (2002) 853±858
857
Lutalyse on Day 8 of the estrous cycle or at a random stage of diestrus. Their study also revealed signi®cant differences in estrus response and conception rates between herds ranging from 56.6 to 74.4% and from 31.8 to 64.7%, respectively. In contrast, Sudweeks et al. [11] detected more Estrumate (65.7%) than Lutalyse-treated heifers (42.7%) in estrus after a single injection. However, they observed no differences in conception rate or total synchrony after a second injection; therefore, the authors concluded Estrumate and Lutalyse were equally effective for synchronization of estrus in heifers. In addition to the lack of MGA pretreatment, the study of Seguin et al. [12] selectively administered PGF2a to cows after ovarian palpation of a corpus luteum or 8 days after a detected standing estrus, which makes any direct comparison to the current study dif®cult. However, all studies suggest that Estrumate and Lutalyse are comparable in their ability to synchronize estrus with no detrimental effect on fertility. Synchrony of estrus was similar between Estrumate- and Lutalyse-treated heifers. Lamb et al. [10] compared the synchrony of estrus after a PGF2a injection administered 17 or 19 days following a 14-day period of MGA feeding. In that study, the 19-day interval resulted in a signi®cant reduction in the average interval to estrus (56 h) compared to the 17-day interval (73 h). Interval to estrus in the present study (64 h) was numerically intermediate to those of Lamb [10]. In both studies, the interval to estrus was shorter than that reported after PGF2a injection during the late-luteal phase (72 h; 7), however, the precision of synchrony in these studies suggests the 14-day MGA PGF2a (19 days later) protocol is capable of producing acceptable pregnancy rates to a single ®xed-time insemination performed at 64±72 h post-PGF2a. In conclusion, cloprostenol (Estrumate) and dinoprost tromethamine (Lutalyse) were equally ef®cacious for synchronous induction of a fertile estrus in virgin beef heifers when administered 19 days after a 14-day MGA feeding period. Although, further research is necessary to con®rm ef®cacy, these results suggest the synchrony of estrus following this protocol is amendable to a ®xed-time insemination protocol with minimal compromise to conception and pregnancy rates.
Acknowledgements The authors thank Bart Kissack, Gillette, WY; Colin Schmidt, Manning, ND; North Dakota State University, Dickinson, ND; Ken Synder, Piedmont, SD; Staurt Land and Cattle Co., Rosedale, VA for the use of their cattle and facilities. We thank the AI technicians at each herd for their technical support and Bayer Animal Health (Shawnee Mission, KS) for the generous donation of the Estrumate1 used in these ®eld trials.
References [1] Lauderdale JW. Effects of PGF2a on pregnancy and estrous cycle of cattle. J Anim Sci 1972;35:246 [Abstract]. [2] Rowson LEA, Tervit R, Brand A. The use of prostaglandin for synchronization of oestrus in cattle. J Reprod Fertil 1972;29:145 [Abstract].
858
R.R. Salverson et al. / Theriogenology 57 (2002) 853±858
[3] Inskeep EK. Potential uses of prostaglandins in control of reproductive cycles of domestic animals. J Anim Sci 1973;36:1149±57. [4] Lauderdale JW, Seguin BE, Stell¯ug JN, Chenault JR, Thatcher WW, Vincent CK, Loyancano AF. Fertility of cattle following PGF2a injection. J Anim Sci 1974;38:964±7. [5] Roche JF. Synchronization of oestrus and fertility following arti®cial insemination in heifers given prostaglandin F2a. J Reprod Fertil 1974;37:135±8. [6] Tanabe TY, Hahn RC. Synchronized estrus and subsequent conception in dairy heifers treated with prostaglandin F2a. I. In¯uence of stage of cycle at treatment. J Anim Sci 1984;58:805±11. [7] Watts TL, Fuquay JW. Response and fertility of dairy heifers following injection with prostaglandin F2a during early, middle or late diestrus. Theriogenology 1985;23:655±61. [8] Beal WE. Current estrus synchronization and arti®cial insemination programs for cattle. J Anim Sci 1998;76(Suppl 3):30±8. [9] Brown LN, Odde KG, King ME, LeFever DG, Neubauer CJ. Comparison of MGA-prostaglandin F2a to syncro-mate B for estrus synchronization in beef heifers. Theriogenology 1988;30:1±12. [10] Lamb GC, Nix DW, Stevenson JS, Corah LR. Prolonging the MGA-prostaglandin F2a interval from 17 to 19 days in an estrus synchronization system for heifers. Theriogenology 2000;53:691±8. [11] Sudweeks EM, Randel RD, Tomaszewski MA. Estrous synchronization after prostaglandin injection in dairy heifers. J Dairy Sci 1983;66(Suppl 1):231 [Abstract]. [12] Seguin B, Momont H, Baumann L. Cloprostenol and dinoprost tromethamine in experimental and ®eld trials treating unobserved estrus in dairy cows. The Bovine Practitioner 1985;20:85±90.
Synchronization of estrus in virgin beef heifers using melengestrol acetate and PGF2a: an ef®cacy comparison of cloprostenol and dinoprost tromethamine R.R. Salverson, J.M. DeJarnette*, C.E. Marshall, R.A. Wallace Select Sires Inc., 11740 U.S. 42, Plain City, OH 43064, USA Received 23 February 2001; accepted 30 April 2001
Abstract This study compared the ef®cacy of two sources of PGF2a on the reproductive performance of virgin beef heifers, after synchronization of estrus using melengestrol acetate (MGA) and PGF2a. Angus-based heifers (n 1002) in ®ve herds were fed 0.5 mg per head per day of MGA for 14 days. Nineteen days after the last day of MGA feeding, heifers were randomly assigned to receive (i.m.) either 0.5 mg cloprostenol (n 504; Estrumate1, E) or 25 mg dinoprost tromethamine (n 498; Lutalyse1, L) as a source of exogenous PGF2a. Heifers were observed twice daily for 5 days for signs of estrus and arti®cially inseminated 8±12 h later, except in herd A, wherein animals not detected in estrus by 80 h after PGF2a were mass-mated and no longer monitored for signs of estrus. Estrumate and Lutalyse were equally (P > 0:1) effective among all response variables evaluated, including estrus response (E, 89% and L, 86%), conception rate (E, 67% and L, 67%), and synchronized pregnancy rate (E, 61% and L, 57%). Synchrony of estrus was not affected (P > 0:1) by PGF2a source, and peak estrus response occurred 60 h post-PGF for both treatments. Conception rate to timed insemination was not different (P > 0:1) among Estrumate- and Lutalyse-treated heifers within herd A (14%, 4/28 and 7%, 2/29, respectively). Herd had a signi®cant (P < 0:05) effect on all indicators of reproductive performance. Conception rates within herds A and D were in¯uenced by technician (P < 0:05), however, this effect was balanced across treatments and no treatment by technician interaction was detected. In conclusion, when administered 19 days after a 14-day MGA feeding period, cloprostenol and dinoprost tromethamine are equally ef®cacious for synchronous induction of a fertile estrus in virgin beef heifers. # 2002 Elsevier Science Inc. All rights reserved. Keywords: PGF2a; Cloprostenol; Dinoprost tromethamine; Estrus synchronization; Melengestrol acetate
* Corresponding author. Tel.: 1-614-8734683; fax: 1-614-8735751. E-mail address: [email protected] (J.M. DeJarnette).
0093-691X/02/$ ± see front matter # 2002 Elsevier Science Inc. All rights reserved. PII: S 0 0 9 3 - 6 9 1 X ( 0 1 ) 0 0 6 9 2 - 6
854
R.R. Salverson et al. / Theriogenology 57 (2002) 853±858
1. Introduction The ability of exogenous PGF2a to regress the corpus luteum present on the ovary of cycling females [1,2] and the subsequent induction of a fertile estrus within 3±5 days [3±5] has facilitated its use in estrus synchronization programs. However, the ability of PGF2a to induce luteal regression is in¯uenced by the stage of the estrous cycle at the time of injection. Early-cycle animals (days 5±9) are less responsive to PGF2a than late-cycle animals (days 13±17) while mid-cycle (days 10±12) animals are intermediate in response [6±8]. Based on these results, Brown et al. [9] developed a synchronization program that includes a 14-day feeding period of melengestrol acetate (MGA), followed with an injection of PGF2a 17 days later. The MGA feeding period can induce cyclicity in some peripubertal heifers and pre-synchronizes corpus luteum development in cyclic animals. Further research with this protocol found a 19-day interval between MGA feeding and PGF2a injection to be slightly more ef®cacious due to the previously described stagedependent responsiveness of the corpus luteum [10]. In most countries, cloprostenol and dinoprost tromethamine are readily available sources of PGF2a; however, limited research has been conducted comparing the ef®cacy of these products [11,12]. Although, limited results indicate the two products are of comparable ef®cacy, no research has compared these products in conjunction with MGA-feedinginduced pre-synchronization of luteal development. The objective of this study was to compare the effects of cloprostenol and dinoprost tromethamine on the reproductive performance of virgin beef heifers synchronized to estrus using MGA and PGF2a. 2. Materials and methods Angus and Angus-based crossbred beef heifers (n 1002) in ®ve herds were fed a grain carrier containing 0.5 mg per head per day of MGA for 14 days. The animals were randomly assigned to receive (i.m.) either 0.5 mg cloprostenol (Estrumate1, Bayer Animal Health, Shawnee Mission, KS; n 504) or 25 mg dinoprost tromethamine (Lutalyse1, Pharmacia Animal Health, Kalamazoo, MI; n 498) 19 days after the last day of MGA feeding as exogenous sources of PGF2a. Four locations observed animals twice daily for signs of estrus for 5 days following the PGF2a injection and bred the heifers by AI 8±12 h after estrus was detected. In herd A, animals were observed and inseminated as previously described until 80 h after the PGF2a, at which time non-responding heifers were ®xed-time inseminated (TAI). Heifers were not exposed to herd bulls for at least 10 days following the last AI. Pregnancy diagnosis was determined via rectal palpation in herd E and by transrectal ultrasonography in all other herds, 30±60 days following a breeding season not exceeding 60 days in length. Data were analyzed using logistic regression and Chi-square procedures. Dependent variables were evaluated in full factorial logistic regression models that included the main effects of herd and treatment (Estrumate or Lutalyse). Due to the shortened estrus detection period, data from herd A (n 292) were not included in analyses of synchrony of estrus. Conception rates per AI were analyzed in the previously described model, with the addition of nested effects of sire within herd and technician with herd. In the absence of signi®cant
Table 1 Within- and across-herd effects of treatment on estrus response, conception, and pregnancy rates Herd
Treatmenta
Detected in estrus (%, number)
Conception rate Standing estrus (%, number)
TAI (%, number) 14 (4/28) 7 (2/29)
Synchronized pregnancy rate (%, number)
A
Estrumate Lutalyse
81 (119/147) 80 (116/145)
67 (80/119) 72 (83/116)
B
Estrumate Lutalyse
97 (87/90) 95 (86/91)
55 (48/87) 46 (40/86)
± ±
53 (48/90) 44 (40/91)
C
Estrumate Lutalyse
90 (46/51) 80 (36/45)
43 (20/46) 50 (18/36)
± ±
39 (20/51) 40 (18/45)
Dc
Estrumate Lutalyse
88 (92/104) 89 (96/108)
85 (77/91) 77 (72/94)
± ±
74 (77/103) 68 (72/106)
Ec
Estrumate Lutalyse
92 (103/112) 86 (94/109)
74 (74/100) 75 (69/92)
± ±
68 (74/109) 64 (69/107)
Totalc
Estrumate Lutalyse
89 (447/504) 86 (428/498)
67 (299/443) 67 (282/424)
a
14 (4/28) 7 (2/29)
57 (84/147) 59 (85/145)
61 (303/500) 57 (284/494)
All heifers received melengestrol acetate (0.5 mg per head per day) for 14 days and an injection (i.m.) of either Estrumate or Lutalyse 19 days after the last day of MGA feeding. b Heifers in herd A that were not detected in estrus by 80 h after prostaglandin treatment were fixed-timed inseminated (TAI). c Discrepancies in n values are due to heifers that were culled, sold, or died subsequent to synchronization of estrus, but prior to pregnancy diagnosis.
R.R. Salverson et al. / Theriogenology 57 (2002) 853±858
b
855
856
R.R. Salverson et al. / Theriogenology 57 (2002) 853±858
Fig. 1. Effects of Estrumate or Lutalyse on the synchrony of estrus in virgin beef heifers. Heifers were fed melengestrol acetate (0.5 mg per head per day) for 14 days followed with an injection (i.m.) of either cloprostenol (0.5 mg; Estrumate) or dinoprost tromethamine (25 mg; Lutalyse) 19 days later. Heifers were observed twice daily for signs of estrus and those not detected in estrus were considered non-responders (NR).
interactions, main effects were evaluated using Chi-square procedures. All statistical analyses were performed using SAS JMP1 Statistical Discovery Software, Version 4.0.2 (SAS Inst., Cary, NC). 3. Results Prostaglandin source had no effect (P > 0:1), within or across herds, on the measures of reproductive performance evaluated in this study. Estrus response was similar (P > 0:1) between treatments (Estrumate, 89% versus Lutalyse, 86%; Table 1), and peak estrus response occurred on an average of 60 h after the PGF2a injection in both treatments (Fig. 1). Irrespective of treatment, herd had a signi®cant effect (P < 0:05) on all indicators of reproductive performance. Conception rates within herds A and D were affected (P < 0:05) by technician; however, this effect was balanced across treatments, and no treatment by technician interaction was detected. Conception rate to timed insemination in herd A did not differ (P > 0:1) between treatments (Estrumate, 14% and Lutalyse, 7%). 4. Discussion Lutalyse and Estrumate demonstrated comparable ef®cacy for synchronous induction of a fertile estrus when administered 19 days following the 14-day period of MGA feeding. However, herd was found to in¯uence all indicators of reproductive performance evaluated. These results are similar to those of Seguin et al. [12], wherein reproductive performance of Holstein dairy cows was similar, following an injection of either Estrumate or
R.R. Salverson et al. / Theriogenology 57 (2002) 853±858
857
Lutalyse on Day 8 of the estrous cycle or at a random stage of diestrus. Their study also revealed signi®cant differences in estrus response and conception rates between herds ranging from 56.6 to 74.4% and from 31.8 to 64.7%, respectively. In contrast, Sudweeks et al. [11] detected more Estrumate (65.7%) than Lutalyse-treated heifers (42.7%) in estrus after a single injection. However, they observed no differences in conception rate or total synchrony after a second injection; therefore, the authors concluded Estrumate and Lutalyse were equally effective for synchronization of estrus in heifers. In addition to the lack of MGA pretreatment, the study of Seguin et al. [12] selectively administered PGF2a to cows after ovarian palpation of a corpus luteum or 8 days after a detected standing estrus, which makes any direct comparison to the current study dif®cult. However, all studies suggest that Estrumate and Lutalyse are comparable in their ability to synchronize estrus with no detrimental effect on fertility. Synchrony of estrus was similar between Estrumate- and Lutalyse-treated heifers. Lamb et al. [10] compared the synchrony of estrus after a PGF2a injection administered 17 or 19 days following a 14-day period of MGA feeding. In that study, the 19-day interval resulted in a signi®cant reduction in the average interval to estrus (56 h) compared to the 17-day interval (73 h). Interval to estrus in the present study (64 h) was numerically intermediate to those of Lamb [10]. In both studies, the interval to estrus was shorter than that reported after PGF2a injection during the late-luteal phase (72 h; 7), however, the precision of synchrony in these studies suggests the 14-day MGA PGF2a (19 days later) protocol is capable of producing acceptable pregnancy rates to a single ®xed-time insemination performed at 64±72 h post-PGF2a. In conclusion, cloprostenol (Estrumate) and dinoprost tromethamine (Lutalyse) were equally ef®cacious for synchronous induction of a fertile estrus in virgin beef heifers when administered 19 days after a 14-day MGA feeding period. Although, further research is necessary to con®rm ef®cacy, these results suggest the synchrony of estrus following this protocol is amendable to a ®xed-time insemination protocol with minimal compromise to conception and pregnancy rates.
Acknowledgements The authors thank Bart Kissack, Gillette, WY; Colin Schmidt, Manning, ND; North Dakota State University, Dickinson, ND; Ken Synder, Piedmont, SD; Staurt Land and Cattle Co., Rosedale, VA for the use of their cattle and facilities. We thank the AI technicians at each herd for their technical support and Bayer Animal Health (Shawnee Mission, KS) for the generous donation of the Estrumate1 used in these ®eld trials.
References [1] Lauderdale JW. Effects of PGF2a on pregnancy and estrous cycle of cattle. J Anim Sci 1972;35:246 [Abstract]. [2] Rowson LEA, Tervit R, Brand A. The use of prostaglandin for synchronization of oestrus in cattle. J Reprod Fertil 1972;29:145 [Abstract].
858
R.R. Salverson et al. / Theriogenology 57 (2002) 853±858
[3] Inskeep EK. Potential uses of prostaglandins in control of reproductive cycles of domestic animals. J Anim Sci 1973;36:1149±57. [4] Lauderdale JW, Seguin BE, Stell¯ug JN, Chenault JR, Thatcher WW, Vincent CK, Loyancano AF. Fertility of cattle following PGF2a injection. J Anim Sci 1974;38:964±7. [5] Roche JF. Synchronization of oestrus and fertility following arti®cial insemination in heifers given prostaglandin F2a. J Reprod Fertil 1974;37:135±8. [6] Tanabe TY, Hahn RC. Synchronized estrus and subsequent conception in dairy heifers treated with prostaglandin F2a. I. In¯uence of stage of cycle at treatment. J Anim Sci 1984;58:805±11. [7] Watts TL, Fuquay JW. Response and fertility of dairy heifers following injection with prostaglandin F2a during early, middle or late diestrus. Theriogenology 1985;23:655±61. [8] Beal WE. Current estrus synchronization and arti®cial insemination programs for cattle. J Anim Sci 1998;76(Suppl 3):30±8. [9] Brown LN, Odde KG, King ME, LeFever DG, Neubauer CJ. Comparison of MGA-prostaglandin F2a to syncro-mate B for estrus synchronization in beef heifers. Theriogenology 1988;30:1±12. [10] Lamb GC, Nix DW, Stevenson JS, Corah LR. Prolonging the MGA-prostaglandin F2a interval from 17 to 19 days in an estrus synchronization system for heifers. Theriogenology 2000;53:691±8. [11] Sudweeks EM, Randel RD, Tomaszewski MA. Estrous synchronization after prostaglandin injection in dairy heifers. J Dairy Sci 1983;66(Suppl 1):231 [Abstract]. [12] Seguin B, Momont H, Baumann L. Cloprostenol and dinoprost tromethamine in experimental and ®eld trials treating unobserved estrus in dairy cows. The Bovine Practitioner 1985;20:85±90.