Use of short-term progestin treatment to resynchronize the second estrus following synchronized breeding in beef heifers

ELSEVIER

USE OF SHORT-TERM PROGESTIN TREATMENT TO RESYNCHRONIZE THE SECOND ESTRUS FOLLOWING SYNCHRONIZED BREEDING IN BEEF HEIFERS H.T Purrs II1 and J.C Whittier2 University of Missouri Columbia, MO 652 11,USA Received for publication. Accepted:

January November

26, 15,

1995 1996

ABSTRACT Two trials were conducted to evaluate the efficacy of short-term progestin administration to resynchronize the second estrus after artificial insemination in yearling beef heifers, In Trial 1 crossbred yearling heifers (n=208) were synchronized with Syncro-Mate-B (SMB) and artificially inseminated (AI) between 48 and 54 h following implant removal. Implant removal is dethmd as Day 1. Following AI, the heifers were randomly assigned to 1 of 2 experimental groups. Group 1 heifers were fed melengestrol acetate (MGA) daily from Day 17 to 21 at a rate of 0.5 mghead, while Group 2 control received no exogenous progestin during this period Synchrony of estrus was defmed as the 3-d period in which the highest number of heifers expressed behavioral estrus in each group. There was no difference (PI &ml) on Day 21 indicated pregnancy to the first insemination, Synchrony among the 3 groups of heifers was similar (P>O.lO); however, the second estrus was less (PcO.05) variable in the MGA and norge&met treated heifers. During the resynchrmrized second estrus, conception rates were not atTected by progestin treatment (MGA 40%, norgestomet 64%, and control 62%; P>O.10). However, a proportion ofheifers treated MGA 10% 4/36 and norgestomet 3% l/36 expressed behavioral estrus during second estrus even though they were diagnosed as pregnant from 6rst service by elevated P4 levels on Day 2 1. We conclude that shortterm use of progestin from Days 17 to 21 following AI causes closer synchrony of estrus; however, inseminating pregnant heifers that exhibit behavioral estrus may cause abortion. Q 1997 by Elsevier Science Inc. Key words: heifers, estrus synchronisation, second e&us, artificial insemination Acknowledgments This study is a contribution from the Missouri Experiment Station. Journal Series No. 12,259. The authors wish to thank David M&tee, Thompson Farm, University of Missouri, Dr. Fred Mark, Forage Systems Research Center; Brad Belew, Animal Science Beef Unit; for assistance in data collecticn and in w&u&g this research. kurrmt address: Animal Science Depatient. Oklahoma State University, Stilhvater, OK 740780452. 2Current address: Animal Science Department. Colorado State University, Ft. Collins, CO 805231171. Theriogenology 48:423-434. 0 1997 by Elsevier Science

1997 Inc.

0093-691X/97/$17.00 PII SOO93-691X(97)00252-5

Theriogenology

INTRODUCTION Artificial insemination is used to increase reproductive etIiciency of beef herds. It also gives producers access to sires with known superior genetic traits. Many factors such as the cost of labor, drugs for estms synchronization, semen and bull maintenance have an impact on the applicaticu of AI technology. Currently, there are several systems for synchrcnizing estms, some of which utilize synthetic progestins alone or in combination with a hneolytic agent (8,9). The advent of such systems make timed insemination possible, which, in turn, reduce labor costs, Pregnancy rates during the first 5 d k&wing synchrcnization of estms with SyncroMate-B@a (SMB) in beef heifers and coyvs have been similar whether the cattle were bred at estms or were insemkated 45 to 60 h after implant removal (6,14). The use of short-term progestins to resynchrcnim heifers that did not conceive to the first inseminaticn may increase the cumulative pregnancy rates while minimizing the time needed for estms detection, Favero et al. (4) reported that norgestomet administered silastic implants cm Day 9 or 12 of the luteal phase and removal on Day 21 caused closer synchrony and higher cumulative pregnancy rates in heifers that did not conceive to timed insemination than in the controls. Use of melqestrol acetate (MGA), an orally active synthetic progestin, has not been evaluated to date in resynchronizing the second e&us. Melmgestrol acetate supplementation to suppress estrus would be less expensive and require less handling of the animals than norgestomet implants. The objectives of our study were 1) determine if oral administration of MGA to heifers &m 17 to 2 1 d after estms synchronization was eftbctive in resyn&rcnizing the return to estms ofheifersthat did not conceive to a timed insemination, and 2) to compare the efficacy of 2 di%xent progestin compounds (MGA or norgestomet) given for 5 d late in the estrous cycle (Days 17 to 21) on the pattern of resynchronimtion and subsequent fertility.

MATFRIALS AND METHODS Trial 1 The first trial was conducted at the University of Missouri l’lmmpscn Farm located in Spickard, Missouri at the Forage Systems Research Center in Linneus, Missouri. Yearling crossbred beef he&s (n=208) were synchrcniaed with the SMB treatment regimen (13) and were artificially inseminated at a preset time between 48 and 54 h atIer implant removal. Equal numbers of heifers per treatment were l3strusdetecti~began2da&ertimedAI randomly assigned to be inseminatedwithsemenfrom3bulls. and continued twice daily for 30 d. Heifers de&ted in estms the first 14 d following the timed kmination were insemkted 12 h after the observed estms, and were excluded from the study. Fourteen days following the timed AI, heifers were randomly allotted, based on breed type, source and Al sire group to 1 of 2 treatmmts (Control or MGA, Figure 1). A ground-corn supplement was fed at a rate of 0.45 kg/head daily to both groups at approximately 8 a.m. each day. The MGA group received 0.5 mg MGAmead daily via the grain supplement, Melengestrol acetate supplemmtati onbegancn Dayl7andcontinuedthrough Day2ltXlowingimplant aSanoti Animal Health, Inc., Gverland Park, KS.

426

Theriogenology

removal. On Day 21 the heifers were combined into 1 group for es&us detection. Heifers were observed for behavioral estrus and were insknated 12 h afler estrus was observed. Bulls were introduced 10 d after MGA t&ding ended and remained with the heifers for 24 d. The heifers were palpated 70 and 120 d ather the start of breeding to diagnose pregnancy and to determine date of conception. Trial2 A second trial was conducted at the University of Missouri Animal Science Beef Unit in Columbia, Missouri. The 108 crossbred heifers (approximately 12.5 to 14.5 mo of age) used in Trial 2 were synchronized for e&us with two injections of PGF2, given 14 d apart. The experimental heifers were selected from the larger group (n=l44) ofheifers based on puberty status and whether they exhibited estrus within 24 to 72 h after the second PGF2o injection. Puberty status was de&mined in an ancillary research project (10) in which twice-weekly blood analyses for P4 concentmtions were done. Equal numbers of heifers per treatment were randomly assigned to 1 of 2 bull groups and were inseminated 12 h post estrus. E&us detection began 2 d atler the seccnd synchroniaed estrus and continued for 30 d. Gn Day 17 after the second PGF2o in'ection, J heifers were randomly assigned by breed, age and sire group to 1 of 3 treatments (MGA, norgestomet, or control) and progestin supplementation was initiated (Figure 2). The heifers received a corn silage and cottonseed-based diet along with a grain-based supplement fed at a rate of 0.45 kg/head daily to all groups at approximately 8 a.m. each day. The MGA group received 0.5 mgkead daily via the grain supplement. A second group of heifers received a 6.0-mg S.C. implant of norgestomet implanted and placed in the convex smfbce of the ear during the same time period that the MGA was fed to heifers in the other treatment group. Melengestrol acetate supplementation and norgestomet implant treatment continued until Day 2 1 following the second PGF2o injection. Heifers were reassigned randomly by tmatment on Day 21 to 1 of 8 pens for estrus detection and were &em&ted 12 h after the observed estrus during the second estrus period. Estrus detection was done twice daily (a.m./p.m.) before implant removal. However, during the second estrus heifers were observed 3 times daily, morning, noon and the evening. Bulls were introduced with heifers 10 d following the cessation MGA &ding and removal norgestomet implants and remained with the heifers for 42 d. The heifers were palpated at 70 and 120 d after the second PGF2o injection to diagnose pregnancy and to determine date of conception. Progesterone Analysis On Day 21 post PGF2o during Trial 2, blood samples were collected via jugular venipuncture and allowed to clot at 5OC. Serum was harvested and immediately assayed for P4 concentmtions, which were determined using a solidphase 1251 IUA Coat-A-count kitb in which 1251 P4 competes with P4 in the sample for specific sites on antibody-coated tubes (5) and has no cross reactivity with the synthetic progestins used in this trial. All samples were analyzed witbin one assay, with a 4.5% i&a-assay coeflicient of variation. Progesterone serum concentration greater than 1 rig/ml was interpreted as evidence of luteal functicn and that the heifer was pregnant. He&m with high P4 levels (>I @ml) were not inseminated ifthey exhibited behavioral es&us during second es&us. oDiagnostic Products Corp., Los Angeles, CA.

m estrus

Second estrus

Synchronized

Norgestomet

MGA

Control

Progestin

supplementation

estrus in heifers following a synchronized breeding in Trial 2

a Day 1 = Second prostaglandin injection b Natural service began 10 days after progestin withdrawal

1

Figure 2 Method used to resynchronize

ljection PGF

ljection PGF

liection PGF

Theriogenology

428 Statistical analysis

Means for conception rates in Trials 1 and 2 were subjected to Chi-square using PROC FREQ of SAS (12). Second estrus responses were analyzed by ranking the mean responses and subjecting ranked means to GLM of SAS (12). Standard deviations around a ranked mean were subjected to a one-sided Ttest (a = 0.05) to evaluate variation between treatment groups. RESULTS AND DISCUSSION Short-term administration of MGA late in the luteal phase caused a more narrow (PcO.05) distribution of estrus in heifers exhibiting estrus during second estrus in Trial 1 and Trial 2. Synchrony in Trial 1 and Trial 2 was detined as the 3d period when the greatest number of heifers expressed behavioral e&us. More heifers during Trial 1 expressed behavioral estrus due to MGA supplementabon than the controls (P
Mean days to e&-us Control 21.9 + 3.9@ MGA 25.0 + 1.53” Progestin removal

20 15 10 5 0 16 19 20 21 22 23 24 25 26 27 26 29 Days after implant removal Figure 3. The effects of MGA on resynchronining the second estrus following timed insem&ion Trial 1. a~bstandard deviations with difikent superscripts differ PCO.05.

in

Theriogenology

429

Synchrony of the second estrus in Trial 2, did not differ among the MGA, norm, or control treatment groups (p>O.lO; 100, 100, 80%; Figure 4). This may be explained by the limited number of heifers available for rehun to estrus. However, standard deviation of the ranked means was the least variable in progestin-treated heifers (PO.lO) between MGA and norgestomet groups, From these data, MGA was as efkctive as norgestomet in synchronizing second estrus of heifers that did not conceive to AI.

0 Control n MGA n Norclestomet

23

24

I

Mean days to estrus

25

22.4 +l .4aa Control 25.5 +.72b MGA Norgestomet 25.8 + .53b

26

27

28

Days after progestin removal Progestin removal Figure 4. The effect of meleqestrol acetate or norgestomet on resynchroniaing second estrus following a s chronized insemination aI?Standard deviation with diRermt superscripts differ PcO.05. The percentage ofheifersthat conceived to timed insemktion during Trial 1 was similar (P>O.40) between control and MGA (24 vs 18%; Table 1) heifers. Pregnancy rates were admktedly low when compared to those of earlier reports of 40 to 66% (13). Decreased pregnancy rates may be explained by heifers not cycling prior to SMB treatment, and therefore not responsive to synchroniaatiar. Heifers used in Trial 1 were purchased from several di&rent sources prior to the breeding season, and were mrtritiamlly underdeveloped at the time purchase.This may explain the low pregnancy rates. Additionally, SMB treatment may have induced estrous behavior in some nonpubertal heifers (9). Byerely et al. (3) reported that inseminating heifers on the third vs first pubertal estrus results in increased conception rates.

of

Theriogenology

431

Therefore, conce@ion rates may reflect decreased tbrtility in heifers that were induced to puberty by SMB treatment. Conception rates (42.5 vs 34.4%), as determined by palpation, ofthe inseminated heifers durhrg the second estrus were similar (p=O.54) between control and MGA heifers. Overall pregnancy rates (60.6 vs 625%) were similar (P=O.56) between control and MGA treated heifers after bull removal. Conception rates tothe syrmhronized estrus in Trial 2 were similar Q=0.69) among control (55%) MGA (58%) and norgetomet (61%; Table 2) treatments. Concepticm data for second estrus in Trial 2 is expressed in 2 forms: animals available for iusemination based on palpation per rectum on Day 70 following the second PGF2o injection, or animals available for insemination based on elevated serum P4 concentraticms collected 21 d following the second PGF2o injection, The discrepancy in the number of animals available for retum to estms (16 vs 14 head for control, 15 vs 12 head for MGA, and 14 vs 12 head for norgestomet) cannot be explained from these data, However, this outcome may represent early embryonic death (1). Animals that were determined to be open by palpation, but that had elevated P4 (>l @ml), did not exhibit behavioral estrus before or during the second estrus. Conception rates for heifers inseminated during second estrus were similar (P=O.33) among control (62%) MGA (40%) and norgestomet (64%) treatments Similar to Trial 1, a numeric, but nonsignifkant (P4.33) reduction in conception rates during second estrus was observed in the MGA treatment. Previous research has shown a reduction in fertility after short-term progestin treatment (5,9). During Trial 2 pregnant heifers exhibited behavioral estrus in both MGA (lo%, 4/36) and norgetomet (3%, l/36) groups, as determined by P4 levels on Day 21 and by palpation per rectum. This may account for the numeric difference in second estrus conception observed in Trial 1 since all heifers exhibiting behavioral e&us were inseminated, which may have disrupted the early development and maintenance of the embryo. Overall pregnancy rates between treatments atIer bull removal were similar (P>O.10) in control (94%), MGA (88%) and norgestomet (88%). It should be noted that in order to resynchronize second estrus with progestins using the protocols outlined in this experiment, a slight delay in the return to second estrus was observed in heifers in both trials as compared with that of the control heifers. Therefore, if this technique were applied in productions systems, mean date of conception during the second estrus period may be slightly later than in heifers that were not resynchronized The success of any synchronization method depends on its ability to successfully group animals in different stages of their cycle within a set amount of time and not reduce subsequent reproductive performance. The observation that fertility is reduced after MGA supplementation is supported by several studies (9,11,15). Reduced fertility in cows treated with progestin late (Day 17) in the estrous cycle is related to a large persistent dominant follicle. The presence of the persistent dominant follicle after progestin may be the cause for reduced fertility following progestin cessation. This result occurs when heifers are fed MGA for longer periods (10 to 18 d) of time than was used in our trials. Patterson et al. (9) reported that supplementation with MGA after Day 12 of the estrous cycle reduced fertility with a 7-d MGA feeding regimen with PGF2, injections. Numeric reductions in concePtion rates at first service have been reported in heifers synchronized with a 5d MGA-PGF2, regimen (7) Extension of the hrteal phase to Day 21 of the estrous cycle with short-term MGA treatment similar to the current experiment decreased conception rates. Conception data in MGA heifers were numerically lower than in the controls.

88

9 44

4 50 94

6 33

15 60 50

16 15 71

2 0

12 15 40

36 58

MGA

14 84 62

36 55

Control

Tr~tmenta

88

5 60

3 0

14 64 75

12 75 64

36 61

Norgestomet

0.64

0.45

0.38

0.65 0.37

0.73 0.33

0.69

Probabilityb

’ Progesterone concentration on Day 2 1 alter second PGFza > 1 ng/ml was interpreted as evidence of pregnancy from prior insemination and tjerefore heifer was unavailable during resynchronization. Palpation per rectum 70 days following first Al Animals less than 70 pregnant were considered to be available during the second estrus.

b Cl&square probability.

a MGA = melengestrol acetate.

Gverall ureansncv (n)

bulls Based on P4 concentration data’ Heifers available (n) Conception (%) Based on palpation datad Heifers available (n) Conception (%)

chll-UD

Second imemination Baaed on P4 concentration datac Heifers available (n) Inseminated (%) conception (%) Based on palpation datad Heifers available (n) Inseminated (%) conception (%)

First insemi~tion Heifers per treatment (n) Conception to syncluonized estrus (%)

Item

Table 2. Pregnancy snd concepuon rates in heifers during Trial 2.

Theriogenology

433

Norgestomet supplementation late in the luteal phase in Trial 2 did not affect fertility during second estrus. Brink and Kiracofe (2) observed reduced conception rates to first service conception in heifers treated late in the h&al phase with SMB implants. However, norgestomet heifers in the current study received a norgestomet (6.0 mg) implant without the injection of estradiol valerate (5.0 mg) and norgestomet (3 .Omg). Additional progestin treatment lasted only 5 d rather than 9 d, which is the normal SMB regimen. Favero et al. (4) reported fertility of cows and heifers were not affected with short-term use ofNOR (3.6~mgor IO-mg implants) implanted on Day 12 through 21 ofthe estrous cycle. The use of short-term progestm supplementation late in the luteal phase can cause closer synchrony in heifers returning to estrus following a timed insemination. Both MGA and norgestomet were effective in resynchronizing the second estrus. Short-term exposure of progestins in the current study using MGA or norgestomet did not significantly decrease fertility compared with that of the controls. Extending the estrous cycle to Day 21 with erogenous P4 may not be sufficient time for dominant follicle establishment compared with extending the hrteal phase for longer periods Numeric reductions in fertility were observed in MGA heifers but not norgestomet heifers compared with that of the controls. Additionally, the observation that pregnant heifers exhibited behavioral es&us after progestin supp1ementation warrants fhrther investigation Overall short-term (5 d) use of progestin late in the estrous cycle following timed insemination may synchronize heifers that do not conceive to insemination and may facilitate subsequent

REFERENCES 1 Bazer FW, Thatcher WW, Hansen PO, Mirando MA, Cht TL, Plan&eC. Physiological mechanisms of pregnancy recognition in ruminants. In proceedings of the 3rd Jntem. Rumin Rqxod Sympo 1990 32:21-23. Brink JT, Kiracofe GH. E&t of estrous cycle stage at Syncro-Mate B treatment and time of estrus in cattle. Theriogenology 1988; 29:513-519. Byerely DJ, Staigmiller RB, Berdinelli JG, Short RE. Pregnancy rates of beef heifers bred either cm pubertal or third estrus. J Anim Sci 1987; 65:645-650. Favero RJ, Faulkner DB, Parrett DF, Kesler DJ. Norgestom& implants synchrcnize estrus and enhance fertility in beef heifers subsequent to a timed artificial insemmation. J Anim Sci 1993; 71:2594-2600. 5. Hamilton S H, Garverick HA, Keisler DH. Characterization of follicle/cyst dynamics and associated endocrine pro&s in dairy cows. Biol Reprod 1995; 53:890-898. 6. Miksch ED, Letbver DG, Mukembo G, Spitzer GC, Wiltbank IN. Synchrtmizaticm of estms in beef cattle. B. Effect of an injection of norgestomet and estrogen in conjunction with a norgestom& implant in heifers and cows. Theriogenology 1978; 10:201-210. Moody EL, McAlhster IF, Lauderdale JW. Effect of PGF2o and MGA on control of the estrous cycle in cattle. J Anim Sci 1978; 65(Suppl1):236 abst. Gdde KG. A review of synchronization of estrus in postpartum cattle. J Anim Sci 1990; 68:817824. Patterson DJ, Corah LR, Kiracofb GH, Stevenson JS, Brethour JR. Conception rate of Bns taums and BQSindiclls crossbred heifers afbsr postwaaning energy manipulation and synchronization of estrus with melengestrol acetate and t&prostalene. J Anim Sci 1989; 67:1138-l 147. 10. Pmvis IJ HT, Whittier JC. EBbcta of ionophore tixding and antebn&c actministration on age and weight of puberty in spring-born beef heifers. J Anim Sci 1996; 74:736-744. 11. Roche IF, Cowely JP. the fertility of heitbrs inseminated at predetermined intervals fbllowing treatmentwithMGAandhCGtocontrolovulation. JReprodFert 1973;35:211-216. 12. SAS. Users Guide: Statistics. SAS Jnstitute Inc., Gary, NC, 1985.

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13. Spitzer JC, Jones DL, Misch ED, Wiltbauk JN. Synchronization ofestrusin beefcattle. III. Field trials using a norgestomet implant and injections of norgestomet and estradiol valerate. llmiogenology 1978; 10:233-240. 14. Spitzer JC, Mares SE, Peterson LA. Pregnancy rate among beef heifers from timed insemhation follawingsynchronizationwithaprogestintreatment. JAnimSci 1981; 53:1-6. 15. Wettemam RP, Hafs HD. Pituitary and gonadal hormones associated with fertile and hfertile inseminations at synchronized estrus. J Anim Sci 1973; 36:716-721. 16. Zimmbleman RG , Lauderdale JW, Sokolowski JH, Schalk TG. Safety and pharmacologic evaluations of melengestrol acetate in cattle and other animals: A review. J Am Vet Med hoc 1970; 157: 1528-1533.