- Email: [email protected]
Case Study : Synchronization of Estrus and Fertility in Gilts Administered P.G. 600® After Treatment with Regu-mate® for 14 or 18 Days
158
The Professional Animal (2002) 18:158–161 EstienneScientist and Harper
of CEstrusS and: Synchronization Fertility in Gilts ASE TUDY
Administered P.G. 600® After Treatment with Regu-mate® for 14 or 18 Days M. J. ESTIENNE1 and A. F. HARPER, PAS Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061
Abstract
(P=0.06) for the 18-d treatment (88.9%) than for the 14-d treatment (63.2%). The objective was to determine the Farrowing rate tended to be greater effects of duration of progestin exposure (P=0.17) for gilts exposed to Regu-mate® prior to gonadotropin treatment on the for 18 d (75%) compared with 14 d synchronization of estrus and fertility in (50%). Total pigs born (P=0.43), pigs gilts. Gilts were fed daily a complete born live (P=0.63), stillborns (P=0.62), diet containing 15 mg Regu-mate® and total litter weight (P=0.52) were (Intervet America Inc., Millsboro, DE) for similar between groups. The number of 14 (n = 19) or 18 (n = 18) d. Twenty-four mummified fetuses tended to be higher hours after the last feeding of Regu(P=0.11) for gilts in the 18-d treatment mate®, all gilts received an i.m. injection group (0.8 ± 0.2) compared with the 14-d of P.G. 600® [400 IU pregnant mare treatment group (0.2 ± 0.3). In sumserum gonadotropin (PMSG) and 200 IU mary, the precision of estrus synchronizahuman chorionic gonadotropin (hCG); tion and reproduction was greater in gilts Intervet America Inc.]. Gilts were bred given P.G. 600® after 18 d compared artificially 12 and 24 h after first detecwith 14-d Regu-mate® treatment. tion of standing estrus. More 18-d (33.3%) than 14-d treated gilts (5.3%) (Key Words: Progestin, Gonadotrowere in estrus on the peak day (d 4.0) pin, Estrus, Gilt.) after P.G. 600® injection (P=0.02). The percentage of gilts displaying estrus ≤7 d after P.G. 600® injection was greater Hormonal methods of synchronizing estrus in replacement gilts would enhance reproductive efficiency by 1To whom correspondence should be ad- allowing more effective use of breeding, gestation, and farrowing units dressed: [email protected]
Introduction
and by facilitating entry of gilts into sow groups when females are bred following weaning. A large proportion of pubertal gilts display estrus approximately 5 d after discontinuation of treatment with an orally active progestin (Regu-mate®; Intervet America Inc., Millsboro, DE). Indeed, a number of studies have demonstrated efficacy of Regu-mate® for synchronizing estrus in gilts when fed at rates of 12.5 to 15 mg/d for 14 to 18 d (2, 4, 8). However, Stevenson and Day (6) and Webel (7) reported that feeding the progestin for 18 d resulted in more precise synchronization of estrus than did a 14-d treatment period. We recently reported a high level of estrous synchronization in gilts that were administered a gonadotropin product (P.G. 600®; Intervet America, Inc.) 24 h after the withdrawal of Regu-mate® (3). In those experiments, the progestin was fed at a rate of 15 mg/d for 18 d (3). The effects of P.G. 600® on the onset of estrus in gilts given Regu-mate® for shorter periods of time have not
CASE STUDY: Estrus Synchronization and Fertility in Gilts
been determined. Thus, the objective of this experiment was to determine the effects of duration of progestin exposure (14 vs 18 d) prior to gonadotropin treatment on the synchronization of estrus and fertility in gilts.
Materials and Methods General. The experiment was conducted at the Swine Research Facility located at the Tidewater Agricultural Research and Extension Center (Suffolk, VA). Thirty-seven Yorkshire × Landrace gilts, 305.9 ± 6.8 d of age (mean ± SE) and 178 ± 2 kg BW, were utilized. Gilts from the research herd typically reach puberty by 180 d of age (3). Thus, for the current investigation, treated gilts were assumed to be sexually mature. Gilts were maintained in groups of three to five in a breeding-gestation building and were allowed 2.7 kg/d of a fortified, corn and soybean mealbased diet that met or exceeded recommendations for the various nutrients (5). Water was available on an ad libitum basis via nipple waterers. Protocol. Gilts were fed 2.7 kg of a complete ration containing 15 mg Regu-mate® for 14 (n = 19) or 18 (n = 18) d, and 24 h after the last feeding of the progestin, all gilts received an i.m. injection of P.G. 600® [400 IU pregnant mare serum gonadotropin (PMSG) and 200 IU human chorionic gonadotropin (hCG)]. Gilts in the 14-d treatment group began receiving Regu-mate® 4 d after gilts in the 18-d group so that progestin withdrawal and P.G. 600® administration occurred on similar days in both treatment groups. Gilts were checked for estrus twice daily at 0700 and 1900 h in the presence of a mature boar and were bred artificially 12 and 24 h after first detected in standing estrus. Semen collected from Landrace boars was utilized, and each insemination dose contained a minimum of three billion spermatozoa. At approximately d 110 of gestation, gilts were moved to individual farrowing crates. At farrow-
ing, the total number of pigs, pigs born live, stillborns, mummified fetuses, and pig BW were determined for each litter. Statistical Analyses. Daily and cumulative percentages of gilts exhibiting estrus (d 3 to d 7 after P.G. 600®) and farrowing rate were analyzed by chi-square analysis using SAS (SAS Institute Inc., Cary, NC). The interval from P.G. 600® to estrus, total number of pigs, pigs born live, stillborns, mummified fetuses, and pig weights were evaluated by ANOVA using the GLM procedure of SAS.
Results The daily and cumulative percentages of Regu-mate®-treated gilts expressing estrus after P.G. 600® are depicted in Figure 1. More 18-d (33%) than 14-d treated gilts (5.3%) were in estrus on the peak day (d 4.0) after gonadotropin injection (P<0.02). Similar proportions (P>0.2) of gilts from each treatment group were in estrus on all other days during the estrous detection period. When comparing cumulative percentages, more 18-d (88.9%) than 14-d
159
(63.2%) treated gilts expressed estrus by d 6.5 or 7 (P=0.06). The P.G. 600®-to-estrus interval was similar (P=0.39) for the 18-d (4.53 ± 0.24 d) and 14-d (4.20 ± 0.28 d) treatments. Reproductive characteristics for Regu-mate®-treated gilts mated after P.G. 600® injection are shown in Table 1. Farrowing rate tended to be greater (P=0.17) in gilts treated with the progestin for 18 d than for 14 d. Total litter size, pigs born live, stillborns, litter BW, pig BW, and length of gestation were similar between groups (P>0.3). There was a tendency (P=0.11) for gilts treated with Regumate® for 18 d to farrow more mummified fetuses than gilts exposed to the progestin for 14 d.
Discussion Previous research demonstrated the ability of Regu-mate® to synchronize estrus in gilts (2, 4, 8). Summarizing previous studies, daily feeding of the progestin at levels of 12.5 to 15 mg/d for 14 to 18 d synchronized estrus in a large proportion of treated individuals. In the U.S., use of Regumate® is allowed in horses, but its
Figure 1. Daily and cumulative percentage of gilts in estrus after cessation of 14- or 18-d treatment with Regu-mate® (15 mg/d; Intervet America Inc., Millsboro, DE). Twenty-four hours following Regu-mate® withdrawal, all gilts received an i.m. injection of P.G. 600® (Intervet America Inc.). More 18-d than 14-d treated gilts were in estrus on d 4.0 after gonadotropin injection (P<0.02). A greater proportion of 18-d than 14-d treated gilts expressed estrus by d 6.5 or d 7 (P=0.06).
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there was a tendency for gilts treated with the progestin for the longer period to farrow more mummified fetuses. The tendencies for gilts given P.G. 600® after 18 d of Regu-mate® Item 14 d 18 d SE P treatment to have a greater farrowing rate and to farrow more mummified Gilts mated 12 16 — — fetuses is not readily explained and a a Gilts farrowing 6 (50) 12 (75) — 0.17 needs to be confirmed in additional Total pigs born 10.1 12.2 2.1 0.43 experiments utilizing larger numbers Pigs born live 9.3 10.3 1.6 0.63 of females. Stillborn 0.6 1.0 0.6 0.62 Mummified fetuses 0.1 0.8 0.3 0.11 In swine breeding herds, it is not Litter BW (kg) 15.5 17.3 2.1 0.52 uncommon to have a group of Pig BW (kg) 1.6 1.6 0.3 0.61 replacement gilts, the cycling status Gestation length (d) 117.0 115.7 0.9 0.30 of which is unknown (e.g., some gilts are prepubertal and others are ranaPercentage of gilts inseminated. domly cycling). Reproductive efficiency would be enhanced by a method that synchronizes estrus in use in swine awaits FDA approval. drawal). These findings are consisthese females. Regu-mate® alone is Estienne et al. (3) recently reported tent with a previous study (6) that highly effective in synchronizing the results of experiments during demonstrated that more 18- than 14- estrus in randomly cycling gilts (2, 4, which Regu-mate® was fed to puberd treated gilts were in estrus 5 d after 8), but is at best marginally efficatal gilts at a level of 15 mg/d for 18 d. Regu-mate® withdrawal. The interval cious at stimulating estrus in prepuTwenty-four hours following progesfrom termination of progestin bertal individuals (7). The P.G. 600®, tin withdrawal, gilts were treated treatment to onset of estrus was on the other hand, stimulates the with P.G. 600®. The combined approximately 5.4 d (6). In that onset of estrus in prepubertal gilts (1, progestin and gonadotropin treatexperiment, gilts were not treated 3) but does not synchronize estrus in ment resulted in a high level of with gonadotropin following proges- cycling females. Thus, a combinaestrous synchronization. Other tin withdrawal. tion of Regu-mate® and P.G. 600® researchers (6, 7) have suggested that In the current experiment, signifi- treatments could be an effective way the precision of estrous synchroniza- cantly more gilts in the 18-d vs the of synchronizing estrus in a group of tion obtained using protocols em14-d treatment group exhibited estrus gilts for which the cycling status is ploying Regu-mate® alone, however, by the end of the estrous detection unknown. Use of P.G. 600® would was affected by duration of progestin period (7 d after P.G. 600® and 8 d stimulate estrus in prepubertal exposure. For example, Webel (7) after Regu-mate® withdrawal). In animals and termination of progestin reported that feeding Regu-mate® for contrast, Stevenson and Davis (6) therapy would result in estrus in 18 d produced more precise synchroreported similar numbers of gilts cycling gilts. Moreover, we recently nization of estrus than did treatment displaying estrus after 14- or 18-d demonstrated that randomly cycling periods of 10, 12, 14, or 16 d. Thus, Regu-mate® treatment. In that gilts given P.G. 600® 24 h after in the current experiment, we sought study, however, estrous detection withdrawal of Regu-mate® had a to determine the effect of duration of continued for 10 d after cessation of higher ovulation rate than did gilts Regu-mate® treatment (14 vs 18 d) on progestin treatment. given Regu-mate® alone (3). the onset of estrus in gilts treated Stevenson and Davis (6) reported In summary, the precision of with P.G. 600®. that percentages of gilts farrowing, estrous synchronization and reproEstrous synchronization was more gestation length, total litter size, and duction were greater in gilts given precise in P.G. 600®-injected gilts that pigs born live and dead were similar P.G. 600® after 18 d compared with had been previously exposed to Regu- in gilts mated after 14- or 18-d Regu14 d. Protocols employing the mate® for 18 d compared with 14 d. mate® treatments. In the current combination of progestin and Indeed, significantly more gilts study, farrowing rates tended to be gonadotropins may enhance reprotreated with the progestin for 18 d greater in gilts given P.G. 600® after ductive efficiency on the swine displayed estrus on d 4 after P.G. treatment with Regu-mate® for 18 vs operation. 600® (5 d after progestin with14 d. Average gestation length and drawal). Overall, the P.G. 600®-tomost litter characteristics (total litter estrus interval was similar between size, pigs born live, stillborns, litter Reproductive efficiency would be groups, averaging 4.4 d (approxiBW, and pig BW) were statistically enhanced by effective methods for mately 5.4 d after Regu-mate® withsimilar between groups. However,
TABLE 1. Fertility in gilts given i.m. P.G. 600® (Intervet America, Inc., Millsboro, DE) after 14 or 18 d of Regu-mate® (Intervet America Inc.) treatment.
Implications
CASE STUDY: Estrus Synchronization and Fertility in Gilts
synchronizing estrus in replacement gilts. The ability to synchronize estrus would allow more efficient scheduling of breeding, gestation, and farrowing units and would facilitate entry of gilts into sow groups when sows are rebred following weaning. The orally active progestin Regu-mate®, which awaits FDA approval for use in swine, effectively synchronizes estrus in cycling gilts. The gonadotropin product P.G. 600® stimulates estrus in prepubertal females. Treatment with the combination of Regu-mate® and P.G. 600® may be an effective tool for synchronizing estrus in a group of gilts, the cycling status of which is unknown. When using the combined Regu-mate® and P.G. 600® protocol, it appears that the precision of estrous synchronization and reproduction is better when the progestin is fed for 18 compared with 14 d.
161
5. National Research Council. 1998. Nutrient Requirements of Swine. (10th Ed.). National Academy Press, Washington, DC.
Literature Cited 1. Britt, J. H., B. N. Day, S. K. Webel, and M. A. Brauer. 1989. Induction of fertile estrus in prepubertal gilts by treatment with a combination of pregnant mare’s serum gonadotropin and human chorionic gonadotropin. J. Anim. Sci. 67:1148. 2. Day, B. N. 1984. Estrous cycle regulation. In Proc. 10th Int. Congr. Anim. Reprod. Artif. Insem., Urbana, IL. 3. Estienne, M. J., A. F. Harper, B. R. Horsley, C. E. Estienne, and J. W. Knight. 2001. Effects of P.G. 600 on the onset of estrus and ovulation rate in gilts treated with Regu-mate. J. Anim. Sci. 79:2757. 4. Gordon, I. 1997. Controlled Reproduction in Pigs. CAB International, Wallingford, Oxon, UK.
6. Stevenson, J. S., and D. L. Davis. 1982. Estrous synchronization and fertility in gilts after 14- or 18-day feeding of altrenogest beginning at estrus or diestrus. J. Anim. Sci. 55:119. 7. Webel, S. K. 1978. Ovulation control in the pig. In Control of Ovulation. D. B. Crighton, N. B. Haynes, G. R. Foxcroft, and G. E. Lamming (Eds.). p 421. Butterworths, London, England. 8. Webel, S. K., and B. N. Day. 1982. The control of ovulation. In Control of Pig Reproduction. D.J.A. Cole and G. R. Foxcroft (Eds.). p 197. Butterworths, London, England.
The Professional Animal (2002) 18:158–161 EstienneScientist and Harper
of CEstrusS and: Synchronization Fertility in Gilts ASE TUDY
Administered P.G. 600® After Treatment with Regu-mate® for 14 or 18 Days M. J. ESTIENNE1 and A. F. HARPER, PAS Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061
Abstract
(P=0.06) for the 18-d treatment (88.9%) than for the 14-d treatment (63.2%). The objective was to determine the Farrowing rate tended to be greater effects of duration of progestin exposure (P=0.17) for gilts exposed to Regu-mate® prior to gonadotropin treatment on the for 18 d (75%) compared with 14 d synchronization of estrus and fertility in (50%). Total pigs born (P=0.43), pigs gilts. Gilts were fed daily a complete born live (P=0.63), stillborns (P=0.62), diet containing 15 mg Regu-mate® and total litter weight (P=0.52) were (Intervet America Inc., Millsboro, DE) for similar between groups. The number of 14 (n = 19) or 18 (n = 18) d. Twenty-four mummified fetuses tended to be higher hours after the last feeding of Regu(P=0.11) for gilts in the 18-d treatment mate®, all gilts received an i.m. injection group (0.8 ± 0.2) compared with the 14-d of P.G. 600® [400 IU pregnant mare treatment group (0.2 ± 0.3). In sumserum gonadotropin (PMSG) and 200 IU mary, the precision of estrus synchronizahuman chorionic gonadotropin (hCG); tion and reproduction was greater in gilts Intervet America Inc.]. Gilts were bred given P.G. 600® after 18 d compared artificially 12 and 24 h after first detecwith 14-d Regu-mate® treatment. tion of standing estrus. More 18-d (33.3%) than 14-d treated gilts (5.3%) (Key Words: Progestin, Gonadotrowere in estrus on the peak day (d 4.0) pin, Estrus, Gilt.) after P.G. 600® injection (P=0.02). The percentage of gilts displaying estrus ≤7 d after P.G. 600® injection was greater Hormonal methods of synchronizing estrus in replacement gilts would enhance reproductive efficiency by 1To whom correspondence should be ad- allowing more effective use of breeding, gestation, and farrowing units dressed: [email protected]
Introduction
and by facilitating entry of gilts into sow groups when females are bred following weaning. A large proportion of pubertal gilts display estrus approximately 5 d after discontinuation of treatment with an orally active progestin (Regu-mate®; Intervet America Inc., Millsboro, DE). Indeed, a number of studies have demonstrated efficacy of Regu-mate® for synchronizing estrus in gilts when fed at rates of 12.5 to 15 mg/d for 14 to 18 d (2, 4, 8). However, Stevenson and Day (6) and Webel (7) reported that feeding the progestin for 18 d resulted in more precise synchronization of estrus than did a 14-d treatment period. We recently reported a high level of estrous synchronization in gilts that were administered a gonadotropin product (P.G. 600®; Intervet America, Inc.) 24 h after the withdrawal of Regu-mate® (3). In those experiments, the progestin was fed at a rate of 15 mg/d for 18 d (3). The effects of P.G. 600® on the onset of estrus in gilts given Regu-mate® for shorter periods of time have not
CASE STUDY: Estrus Synchronization and Fertility in Gilts
been determined. Thus, the objective of this experiment was to determine the effects of duration of progestin exposure (14 vs 18 d) prior to gonadotropin treatment on the synchronization of estrus and fertility in gilts.
Materials and Methods General. The experiment was conducted at the Swine Research Facility located at the Tidewater Agricultural Research and Extension Center (Suffolk, VA). Thirty-seven Yorkshire × Landrace gilts, 305.9 ± 6.8 d of age (mean ± SE) and 178 ± 2 kg BW, were utilized. Gilts from the research herd typically reach puberty by 180 d of age (3). Thus, for the current investigation, treated gilts were assumed to be sexually mature. Gilts were maintained in groups of three to five in a breeding-gestation building and were allowed 2.7 kg/d of a fortified, corn and soybean mealbased diet that met or exceeded recommendations for the various nutrients (5). Water was available on an ad libitum basis via nipple waterers. Protocol. Gilts were fed 2.7 kg of a complete ration containing 15 mg Regu-mate® for 14 (n = 19) or 18 (n = 18) d, and 24 h after the last feeding of the progestin, all gilts received an i.m. injection of P.G. 600® [400 IU pregnant mare serum gonadotropin (PMSG) and 200 IU human chorionic gonadotropin (hCG)]. Gilts in the 14-d treatment group began receiving Regu-mate® 4 d after gilts in the 18-d group so that progestin withdrawal and P.G. 600® administration occurred on similar days in both treatment groups. Gilts were checked for estrus twice daily at 0700 and 1900 h in the presence of a mature boar and were bred artificially 12 and 24 h after first detected in standing estrus. Semen collected from Landrace boars was utilized, and each insemination dose contained a minimum of three billion spermatozoa. At approximately d 110 of gestation, gilts were moved to individual farrowing crates. At farrow-
ing, the total number of pigs, pigs born live, stillborns, mummified fetuses, and pig BW were determined for each litter. Statistical Analyses. Daily and cumulative percentages of gilts exhibiting estrus (d 3 to d 7 after P.G. 600®) and farrowing rate were analyzed by chi-square analysis using SAS (SAS Institute Inc., Cary, NC). The interval from P.G. 600® to estrus, total number of pigs, pigs born live, stillborns, mummified fetuses, and pig weights were evaluated by ANOVA using the GLM procedure of SAS.
Results The daily and cumulative percentages of Regu-mate®-treated gilts expressing estrus after P.G. 600® are depicted in Figure 1. More 18-d (33%) than 14-d treated gilts (5.3%) were in estrus on the peak day (d 4.0) after gonadotropin injection (P<0.02). Similar proportions (P>0.2) of gilts from each treatment group were in estrus on all other days during the estrous detection period. When comparing cumulative percentages, more 18-d (88.9%) than 14-d
159
(63.2%) treated gilts expressed estrus by d 6.5 or 7 (P=0.06). The P.G. 600®-to-estrus interval was similar (P=0.39) for the 18-d (4.53 ± 0.24 d) and 14-d (4.20 ± 0.28 d) treatments. Reproductive characteristics for Regu-mate®-treated gilts mated after P.G. 600® injection are shown in Table 1. Farrowing rate tended to be greater (P=0.17) in gilts treated with the progestin for 18 d than for 14 d. Total litter size, pigs born live, stillborns, litter BW, pig BW, and length of gestation were similar between groups (P>0.3). There was a tendency (P=0.11) for gilts treated with Regumate® for 18 d to farrow more mummified fetuses than gilts exposed to the progestin for 14 d.
Discussion Previous research demonstrated the ability of Regu-mate® to synchronize estrus in gilts (2, 4, 8). Summarizing previous studies, daily feeding of the progestin at levels of 12.5 to 15 mg/d for 14 to 18 d synchronized estrus in a large proportion of treated individuals. In the U.S., use of Regumate® is allowed in horses, but its
Figure 1. Daily and cumulative percentage of gilts in estrus after cessation of 14- or 18-d treatment with Regu-mate® (15 mg/d; Intervet America Inc., Millsboro, DE). Twenty-four hours following Regu-mate® withdrawal, all gilts received an i.m. injection of P.G. 600® (Intervet America Inc.). More 18-d than 14-d treated gilts were in estrus on d 4.0 after gonadotropin injection (P<0.02). A greater proportion of 18-d than 14-d treated gilts expressed estrus by d 6.5 or d 7 (P=0.06).
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Estienne and Harper
there was a tendency for gilts treated with the progestin for the longer period to farrow more mummified fetuses. The tendencies for gilts given P.G. 600® after 18 d of Regu-mate® Item 14 d 18 d SE P treatment to have a greater farrowing rate and to farrow more mummified Gilts mated 12 16 — — fetuses is not readily explained and a a Gilts farrowing 6 (50) 12 (75) — 0.17 needs to be confirmed in additional Total pigs born 10.1 12.2 2.1 0.43 experiments utilizing larger numbers Pigs born live 9.3 10.3 1.6 0.63 of females. Stillborn 0.6 1.0 0.6 0.62 Mummified fetuses 0.1 0.8 0.3 0.11 In swine breeding herds, it is not Litter BW (kg) 15.5 17.3 2.1 0.52 uncommon to have a group of Pig BW (kg) 1.6 1.6 0.3 0.61 replacement gilts, the cycling status Gestation length (d) 117.0 115.7 0.9 0.30 of which is unknown (e.g., some gilts are prepubertal and others are ranaPercentage of gilts inseminated. domly cycling). Reproductive efficiency would be enhanced by a method that synchronizes estrus in use in swine awaits FDA approval. drawal). These findings are consisthese females. Regu-mate® alone is Estienne et al. (3) recently reported tent with a previous study (6) that highly effective in synchronizing the results of experiments during demonstrated that more 18- than 14- estrus in randomly cycling gilts (2, 4, which Regu-mate® was fed to puberd treated gilts were in estrus 5 d after 8), but is at best marginally efficatal gilts at a level of 15 mg/d for 18 d. Regu-mate® withdrawal. The interval cious at stimulating estrus in prepuTwenty-four hours following progesfrom termination of progestin bertal individuals (7). The P.G. 600®, tin withdrawal, gilts were treated treatment to onset of estrus was on the other hand, stimulates the with P.G. 600®. The combined approximately 5.4 d (6). In that onset of estrus in prepubertal gilts (1, progestin and gonadotropin treatexperiment, gilts were not treated 3) but does not synchronize estrus in ment resulted in a high level of with gonadotropin following proges- cycling females. Thus, a combinaestrous synchronization. Other tin withdrawal. tion of Regu-mate® and P.G. 600® researchers (6, 7) have suggested that In the current experiment, signifi- treatments could be an effective way the precision of estrous synchroniza- cantly more gilts in the 18-d vs the of synchronizing estrus in a group of tion obtained using protocols em14-d treatment group exhibited estrus gilts for which the cycling status is ploying Regu-mate® alone, however, by the end of the estrous detection unknown. Use of P.G. 600® would was affected by duration of progestin period (7 d after P.G. 600® and 8 d stimulate estrus in prepubertal exposure. For example, Webel (7) after Regu-mate® withdrawal). In animals and termination of progestin reported that feeding Regu-mate® for contrast, Stevenson and Davis (6) therapy would result in estrus in 18 d produced more precise synchroreported similar numbers of gilts cycling gilts. Moreover, we recently nization of estrus than did treatment displaying estrus after 14- or 18-d demonstrated that randomly cycling periods of 10, 12, 14, or 16 d. Thus, Regu-mate® treatment. In that gilts given P.G. 600® 24 h after in the current experiment, we sought study, however, estrous detection withdrawal of Regu-mate® had a to determine the effect of duration of continued for 10 d after cessation of higher ovulation rate than did gilts Regu-mate® treatment (14 vs 18 d) on progestin treatment. given Regu-mate® alone (3). the onset of estrus in gilts treated Stevenson and Davis (6) reported In summary, the precision of with P.G. 600®. that percentages of gilts farrowing, estrous synchronization and reproEstrous synchronization was more gestation length, total litter size, and duction were greater in gilts given precise in P.G. 600®-injected gilts that pigs born live and dead were similar P.G. 600® after 18 d compared with had been previously exposed to Regu- in gilts mated after 14- or 18-d Regu14 d. Protocols employing the mate® for 18 d compared with 14 d. mate® treatments. In the current combination of progestin and Indeed, significantly more gilts study, farrowing rates tended to be gonadotropins may enhance reprotreated with the progestin for 18 d greater in gilts given P.G. 600® after ductive efficiency on the swine displayed estrus on d 4 after P.G. treatment with Regu-mate® for 18 vs operation. 600® (5 d after progestin with14 d. Average gestation length and drawal). Overall, the P.G. 600®-tomost litter characteristics (total litter estrus interval was similar between size, pigs born live, stillborns, litter Reproductive efficiency would be groups, averaging 4.4 d (approxiBW, and pig BW) were statistically enhanced by effective methods for mately 5.4 d after Regu-mate® withsimilar between groups. However,
TABLE 1. Fertility in gilts given i.m. P.G. 600® (Intervet America, Inc., Millsboro, DE) after 14 or 18 d of Regu-mate® (Intervet America Inc.) treatment.
Implications
CASE STUDY: Estrus Synchronization and Fertility in Gilts
synchronizing estrus in replacement gilts. The ability to synchronize estrus would allow more efficient scheduling of breeding, gestation, and farrowing units and would facilitate entry of gilts into sow groups when sows are rebred following weaning. The orally active progestin Regu-mate®, which awaits FDA approval for use in swine, effectively synchronizes estrus in cycling gilts. The gonadotropin product P.G. 600® stimulates estrus in prepubertal females. Treatment with the combination of Regu-mate® and P.G. 600® may be an effective tool for synchronizing estrus in a group of gilts, the cycling status of which is unknown. When using the combined Regu-mate® and P.G. 600® protocol, it appears that the precision of estrous synchronization and reproduction is better when the progestin is fed for 18 compared with 14 d.
161
5. National Research Council. 1998. Nutrient Requirements of Swine. (10th Ed.). National Academy Press, Washington, DC.
Literature Cited 1. Britt, J. H., B. N. Day, S. K. Webel, and M. A. Brauer. 1989. Induction of fertile estrus in prepubertal gilts by treatment with a combination of pregnant mare’s serum gonadotropin and human chorionic gonadotropin. J. Anim. Sci. 67:1148. 2. Day, B. N. 1984. Estrous cycle regulation. In Proc. 10th Int. Congr. Anim. Reprod. Artif. Insem., Urbana, IL. 3. Estienne, M. J., A. F. Harper, B. R. Horsley, C. E. Estienne, and J. W. Knight. 2001. Effects of P.G. 600 on the onset of estrus and ovulation rate in gilts treated with Regu-mate. J. Anim. Sci. 79:2757. 4. Gordon, I. 1997. Controlled Reproduction in Pigs. CAB International, Wallingford, Oxon, UK.
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