J. Anim Sci. 2008. 86:1519-1525. doi:10.2527/jas.2008-0925
© 2008 American Society of Animal Science
ANIMAL GROWTH, PHYSIOLOGY, AND REPRODUCTION |
Timing of artificial insemination in postpartum beef cows following administration of the CO-Synch + controlled internal drug-release protocol1
D. C. Busch*,
D. J. Schafer
,
D. J. Wilson*,
D. A. Mallory*,
N. R. Leitman*,
J. K. Haden,
M. R. Ellersieck
,
M. F. Smith* and
D. J. Patterson*,2
* Division of Animal Science, S132 ASRC, University of Missouri, Columbia 65211;
and
MFA Inc., 201 Ray Young Dr., Columbia, MO 65201; and
Agriculture Experiment Station, University of Missouri, Columbia 65211
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Abstract
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This experiment was designed to compare pregnancy rates in postpartum beef cows resulting from fixed-time AI (FTAI) at 54 or 66 h after administration of the CO-Synch + controlled internal drug-release (CIDR) protocol. Cows (n = 851) at 2 locations over 2 yr (yr 1, n = 218 and 206; and yr 2, n = 199 and 228 at the 2 locations, respectively) were stratified by age, BCS, and days postpartum to 1 of 2 FTAI intervals. Cows were administered GnRH (100 µg, i.m.) and were equipped with a CIDR insert (1.38 g of progesterone) on d 0. Controlled internal drug-release inserts were removed 7 d later at the time PGF2
(25 mg, i.m.) was administered (d 7). Continuous estrus detection was performed at location 2 by using the HeatWatch Estrus Detection System; the transmitters were fitted at the time of PGF2 and removed at the time of AI. Artificial insemination was performed at predetermined fixed times [54 h (FTAI 54; n = 424) or 66 h (FTAI 66; n = 427) after PGF2] and all cows were administered GnRH (100 µg, i.m.) at AI. Two blood samples were collected on d –10 or –8 and immediately before treatment initiation to determine the pretreatment estrous cyclicity status of cows [progesterone 
0.5 ng/mL (FTAI 54, 288/424 = 68%; FTAI 66, 312/427 = 73%; P = 0.07)]. Pregnancy rates were greater (P < 0.01) among cows that exhibited estrus than among those that did not (123/163 = 76% and 150/270 = 56%, respectively). There were no treatment x location interactions within year (P > 0.10) for age, days postpartum, or BCS; thus, the results were pooled for the respective treatments. Pregnancy rates were greater for FTAI 66 than FTAI 54 (P = 0.05; 286/426 = 67% vs. 257/424 = 61%, respectively). Pregnancy rates resulting from FTAI did not differ between year (P = 0.09), farm (P = 0.80), AI sire (P = 0.11), or technician (P = 0.64). There was no difference between pregnancy rates resulting from FTAI based on pretreatment cyclicity status (P = 0.30), and there was no difference between treatments in final pregnancy rates (P = 0.77). In summary, pregnancy rates resulting from FTAI following CO-Synch + CIDR at 66 h were greater than those resulting from FTAI at 54 h.
Key Words: artificial insemination • beef cow • controlled internal drug-release insert • estrous synchronization • pregnancy rate
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INTRODUCTION
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Estrous synchronization and AI offer beef producers the means to introduce proven superior genetics into their herds, shorten the calving season, and increase calf age and uniformity. However, surveys indicate fewer than 10% of beef cows in the United States are bred by AI (National Animal Health Monitoring System, 1997
), and even fewer beef operations use estrous synchronization to facilitate AI programs (National Animal Health Monitoring System, 1997). The main reason producers cited for not implementing these 2 practices was "lack of available time and labor" (National Animal Health Monitoring System, 1998). Therefore, to enhance the use of estrous synchronization and AI by beef producers, effective estrous synchronization protocols need to minimize the number and frequency of animal handlings and minimize or eliminate the need for estrus detection. Development of methods to control estrous cycles in cattle that result in expression of a highly synchronized and fertile estrus and ovulation will more readily facilitate fixed-time AI (FTAI; Patterson et al., 2003a). Effective estrous synchronization protocols that facilitate FTAI would likely increase the adoption of AI in beef herds (Patterson et al., 2003b).
Previous research demonstrated the efficacy of using the CO-Synch + controlled internal drug-release (CIDR) protocol to synchronize estrus and ovulation when FTAI was performed at 66 h after administration of PGF2 (Schafer et al., 2007). Another study demonstrated a numerical improvement in pregnancy rates with FTAI at 66 h compared with 48 or 54 h after PGF2 (Bremer et al., 2004). However, Dobbins et al. (2006) reported an improvement in pregnancy rates resulting from FTAI at 56 to 64 h compared with 48 or 72 h after PGF2.
Therefore, the objective of this experiment was to compare FTAI pregnancy rates among lactating beef cows synchronized with the CO-Synch + CIDR protocol and inseminated at 54 or 66 h after PGF2, and to characterize the estrous response of cows in each treatment group before FTAI.
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MATERIALS AND METHODS
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The experimental procedures were approved by the University of Missouri-Columbia Animal Care and Use Committee.
Animals
Crossbred lactating beef cows (n = 851) at 2 locations over 2 yr (yr 1, n = 218 and 206; and yr 2, n = 199 and 228 at the 2 locations, respectively) were assigned within age group (2 to 15 yr) by calving date (days postpartum; DPP) and BCS (1 to 9 scale; 1 = emaciated and 9 = obese; Richards et al., 1986) to 1 of 2 FTAI times (Table 1). Cows synchronized with the CO-Synch + CIDR protocol received GnRH (100 µg, i.m.; Cystorelin, Merial, Athens, GA) and an Eazi-Breed CIDR insert (1.38 g of progesterone; Pfizer Animal Health, New York, NY) on d 0 and PGF2 (25 mg, i.m.; Lutalyse, Pfizer Animal Health, New York, NY) and CIDR insert removal on d 7. Cows at location 2 were fitted with HeatWatch Estrus Detection System transmitters (DDx Inc., Denver, CO) at the time of PGF2 to characterize the estrous response (estrus was defined as cows receiving 3 mounts, each of which was 2 s in duration, within a 4-h period) before FTAI, at which time the transmitters were removed. Fixed-time AI was performed at 54 (n = 424) or 66 h (n = 427) after PGF2 (Figure 1). Times of PGF2 administration and AI were recorded for each cow. All cows were administered GnRH (100 µg, i.m) at the time of insemination, and AI was performed by 1 of 2 experienced technicians. During yr 1 of the experiment, 1 sire was used at location 1 and 3 sires were used at location 2. During yr 2 of the experiment, the same 2 sires were used at both locations. The sire used during yr 1 at location 1 was also one of the sires used at location 2 during yr 1, and at both locations during yr 2. The AI sires were assigned to cows within each treatment by age, calving date, and BCS. Artificial insemination technicians were assigned to cows within each treatment by AI sire, cow age, calving date, and BCS. Twelve to 14 d after FTAI, cows were exposed to fertile bulls for the remainder of the 60-d breeding season.
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Table 1. Number of cows at each location, age, days postpartum, BCS, and cyclicity status for cows before the initiation of treatment (means ± SE)
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Figure 1. Treatment schedule for cows assigned to the CO-Synch + controlled internal drug-release (CIDR) protocol with fixed time AI (FTAI) at 54 or 66 h. Cows synchronized with the CO-Synch + CIDR protocol received an Eazi-Breed CIDR insert (Pfizer Animal Health, New York, NY; 1.38 g of progesterone) and were administered GnRH (Cystorelin, Merial, Athens, GA; 100 µg, i.m.) on d 0. On d 7, the CIDR insert was removed and PGF2 (PG; 25 mg, i.m. Lutalyse, Pfizer Animal Health) was administered. At 54 or 66 h after CIDR insert removal and PG, the cows received GnRH and FTAI.
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Blood Collection and RIA
Blood samples were collected via jugular venipuncture into 10-mL Vacutainer tubes (Fisher Scientific, Pittsburgh, PA) at d –10 or –8 and immediately before treatment initiation (d 0) to determine pretreatment estrous cyclicity status. Blood samples were allowed to clot and were stored at 4°C for 24 h. Serum was collected by centrifugation (2,000 x g for 20 min) and was stored at –20°C until hormone analyses were performed. Serum concentrations of progesterone were determined with a Coat-A-Count Kit (Diagnostic Products Corporation, Los Angeles, CA; Kirby et al., 1997), with intra-and interassay CV of 2.3 and 11.4% and an assay sensitivity of 0.1 ng/mL. Cows were considered cyclic if their progesterone concentrations were 0.5 ng/mL in one or both blood samples before treatment initiation (Ciccioli et al., 2003).
Pregnancy Diagnosis
Pregnancy rate to AI was determined by transrectal ultrasonography (Aloka 500V equipped with a 5.0-MHz linear-array transducer; Aloka, Wallingford, CT) 56 to 78 d after FTAI. Final pregnancy rates were determined by transrectal ultrasonography or rectal palpation 60 to 110 d after the end of the 60-d breeding season.
Statistical Analysis
Differences in age, DPP, and BCS between treatments were analyzed by ANOVA using the statistical model with year, location, treatment, and all relevant interactions (PROC GLM; SAS Inst. Inc., Cary, NC). Pretreatment cyclicity status was analyzed by 
2 analysis (PROC GENMOD of SAS) using the model with year, location, treatment, and all relevant interactions. Estrous response, pregnancy rate to FTAI, and final pregnancy rate at the end of the breeding season were analyzed by 2 analysis (PROC GENMOD of SAS) using the model with year, location, treatment, AI technician, pretreatment estrous cyclicity status, and all relevant interactions. The odds ratio was calculated by taking the inverse natural log of the regression coefficient estimate from the GENMOD procedure. Differences in interval from PGF2 to estrus and FTAI (location 2) were determined by ANOVA using the statistical model with year, treatment, pretreatment cyclicity status, and all relevant interactions (PROC GLM of SAS).
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RESULTS
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The number of cows, mean age, DPP, BCS, and cyclicity rate of cows before the initiation of treatments are shown for each location during each year in Table 1
. There were no differences between treatments at the respective locations for age (P = 0.94), DPP (P = 0.96), BCS (P = 0.77), or cyclicity status (P = 0.07) at the initiation of treatment; however, there were differences in DPP, BCS and cyclicity rate between locations and years, and a location x year interaction in DPP and BCS (P < 0.05; Table 1).
The interval from PGF2 to FTAI (mean ± SD) was 54.2 ± 0.5 and 66.2 ± 0.4 for cows in the FTAI at 54-and 66-h treatments, respectively. There was no effect of year (P = 0.09), location (P = 0.80), technician (P = 0.64), sire (P = 0.11), or pretreatment cyclicity status before initiation of treatment (P = 0.30; Table 2) on pregnancy rates resulting from FTAI. However, there was a significant effect (P = 0.05) of treatment on pregnancy rates resulting from FTAI among all cows (Table 3). On the basis of the odds ratio, cows inseminated at 66 h following PGF2 administration are 1.32 times more likely to conceive to the FTAI than cows inseminated at 54 h following PGF2 administration. Final pregnancy rate at the end of the 60-d breeding season did not differ (P = 0.77) between treatments (Table 3).
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Table 2. Pregnancy rates after fixed-time AI (FTAI) based on estrous cyclicity before the initiation of treatments1
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Estrous response (location 2) following PGF2 and before FTAI was greater (P < 0.01) among cows inseminated at 66 h (50%) than among cows inseminated at 54 h (26%). However, there was no difference (P > 0.10) in estrous response (location 2) within treatment between cyclic and anestrous cows and no overall difference (P = 0.21) between cyclic and anestrous cows. Mean interval from PGF2 to estrus was shorter (P < 0.01) for FTAI at 54 h (mean ± SE, 46.7 ± 1.1 h) compared with FTAI at 66 h (53.8 ± 1.0 h); however, these differences occurred as a result of the HeatWatch transmitters being removed at AI. Cows that exhibited estrus before FTAI had significantly greater pregnancy rates (76%; P < 0.01) than cows that did not exhibit estrus before AI (56%; Table 4). In addition, cows that exhibited estrus before FTAI at 66 h had a greater pregnancy rate (81%; P = 0.03) than cows that exhibited estrus before FTAI at 54 h (65%; Table 4).
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DISCUSSION
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Estrous synchronization for beef heifers and cows has been commercially available to producers for more than 30 yr; however, the beef industry has been slow to adopt this technology. Estrous synchronization protocols that include treatment with a progestin offer the potential to initiate estrous cyclicity in anestrous cows, more effectively facilitate AI, and shorten the subsequent calving period, resulting in a more uniform calf crop. In addition, recently developed estrous synchronization protocols for postpartum beef cows facilitate FTAI and eliminate the time and labor required for estrus detection without compromising pregnancy rates resulting from AI (Bader et al., 2005; Larson et al., 2006; Schafer et al., 2007). Several studies involving the CO-Synch + CIDR protocol have evaluated the effect of timing of AI on subsequent pregnancy rates resulting from FTAI, with insemination times varying from 48 to 72 h after PGF2 (Bremer et al., 2004; Dobbins et al., 2006). However, there are no conclusive results demonstrating that AI should be performed at a specific time following the CO-Synch + CIDR protocol. Timing of insemination following the CO-Synch + CIDR protocol was based on recommendations from the pharmaceutical and AI industries of 60 ± 6 h (54 to 66 h; North Central Region Bovine Reproductive Task Force, 2006) and other reports in which the timing of AI included 48, 54, 56, 60, 64, 66, and 72 h post PGF2 (Lamb et al., 2001; Bremer et al., 2004; Dobbins et al., 2006; Larson et al., 2006; Schafer et al., 2007).
In this study, performing FTAI at 66 h after PGF2 administration and CIDR insert removal following treatment with the CO-Synch + CIDR protocol resulted in an improved estrous response before FTAI and a greater FTAI pregnancy rate compared with insemination performed at 54 h. Improved pregnancy rates following FTAI at 66 h appear to be associated with the increased estrous response before FTAI. Larson et al. (2006) reported that the peak estrous response following the Select Synch + CIDR protocol occurred 48 to 60 h after PGF2 administration, with a mean interval to estrus of 53.4 ± 0.8 h. Those results are similar to data reported in this study (53.8 ± 1.0 h) for cows inseminated at 66 h. On the basis of the Larson et al. (2006) data, using the general rule of inseminating cows 12 h after the onset of estrus, the peak time of insemination with the CO-Synch + CIDR protocol should occur 60 to 72 h after PGF2, which includes the time period (66 h) in this study in which the greatest FTAI pregnancy rate was obtained.
The onset of estrus before FTAI in beef cows was shown to improve pregnancy rates compared with cows that did not exhibit estrus (Perry et al., 2005). Our data are similar to those of Perry et al. (2005), who reported that cows that exhibited estrus before or at AI had greater pregnancy rates (90%) than cows that had not yet exhibited estrus (29%; P < 0.01) following administration of the CO-Synch protocol. Busch et al. (2008) reported that cows that exhibited estrus following administration of the CO-Synch protocol had greater serum estradiol concentrations during the 2 d before insemination compared with cows that were induced to ovulate. Cows that exhibited estrus in the current study may have attained concentrations of estradiol necessary to effectively prepare follicular cells for luteinization, or may have induced an adequate number of uterine progesterone receptors, or both (Zelinski et al., 1980), thus providing an adequate uterine environment for pregnancy establishment and maintenance. These data indicate that greater estrous response rates before FTAI in beef cows should result in greater pregnancy rates resulting from FTAI, provided that AI is performed within an acceptable time period following the peak estrous period. However, to date no studies have characterized the full estrus distribution following the CO-Synch + CIDR protocol to identify the peak estrous period.
It is important to note that there was no difference within treatments in pregnancy rates resulting from FTAI between cows that were classified as cyclic or anestrus before treatment initiation. These results indicate that the CO-Synch + CIDR protocol effectively induced cyclicity in anestrous cows as measured by estrus, ovulation, and pregnancy outcome. The authors acknowledge the similarity in pregnancy rates between treatments at location 1; however, a difference was observed at location 2 during both years of the study (Table 3). This may be partially explained by the slight difference that was noted in the distribution of cows exhibiting estrus among anestrous and cyclic cows at location 2 following PGF2 (Figure 2). At location 2, anestrous cows seemed to express estrus earlier than cyclic cows following CIDR removal and PGF2 administration, based on the small number of anestrous cows (n = 36) that expressed estrus in this study. Therefore, the similarity in FTAI pregnancy rates at location 1 may be due to the increased number of anestrous cows (40 vs. 19% anestrous; location 1 and 2, respectively) that expressed estrus earlier and the fact that more of those cows conceived to the 54-h FTAI compared with location 2.
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Figure 2. Percentage of anestrous or cyclic cows in estrus during the interval between receiving PGF2 (PG) and fixed-time AI at location 2.
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A key observation from this study lies with the fact that pregnancy rates resulting from FTAI at 66 h following administration of the CO-Synch + CIDR protocol were consistent across locations and years. These results too, as they relate to pregnancy rates following FTAI, compare favorably with the study by Schafer et al. (2007) and with the field trials in Missouri reported by Patterson et al. (2007). Interestingly, these results are consistently greater than those reported in the literature (Lamb et al., 2001; Bremer et al., 2004; Dobbins et al., 2006; Larson et al., 2006) when cows were inseminated at 48, 56, 60, 64, or 72 h following treatment administration, all of which point to the importance of timing of insemination and the associated impact on pregnancy outcome.
Finally, the authors acknowledge the potential for misclassification of cows on the basis of cyclicity determined from 2 blood samples before treatment initiation and the use of progesterone values 0.5 ng/mL to confirm cyclicity. However, the potential for committing a type II error is greatly minimized, if not negated, in describing cows as anestrus when using a 0.5-ng/mL cutoff.
These results indicate that greater pregnancy rates may be achieved through a single insemination following administration of the CO-Synch + CIDR protocol when FTAI is performed at 66 versus 54 h after PGF2. This protocol affords producers the opportunity to perform AI at a predetermined fixed time and eliminate the time and labor required to detect estrus and inseminate cows over multiple days.
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Footnotes
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1 Contribution from the Missouri Agric. Exp. Stn. This project was supported by Select Sires Inc. (Plain City, OH). The authors gratefully acknowledge Pfizer Animal Health (New York, NY) for providing the Lutalyse sterile solution and Eazi-Breed CIDR cattle inserts; Merial (Athens, GA) for providing the Cystorelin; Select Sires Inc. for providing the semen; and D. S. McAtee and J. J. D. Schreffler for their dedicated support of this research at the University of Missouri Thompson Farm (Spickard, MO). 
2 Corresponding author: pattersond{at}missouri.edu
Received for publication February 4, 2008.
Accepted for publication March 12, 2008.
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LITERATURE CITED
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Bader, J. F., F. N. Kojima, D. J. Schafer, J. E. Stegner, M. R. Ellersieck, M. F. Smith, and D. J. Patterson. 2005. A comparison of progestin-based protocols to synchronize ovulation and facilitate fixed-time artificial insemination in postpartum beef cows. J. Anim. Sci. 83:136–143.[Abstract/Free Full Text]
Bremer, V. R., S. M. Damiana, F. A. Ireland, D. B. Faulkner, and D. J. Kesler. 2004. Optimizing the interval from PGF to timed AI in the CO-Synch+CIDR and 7–11 Synch estrus synchronization protocols for postpartum beef cows. J. Anim. Sci. 82(Suppl. 2):106.
Busch, D. C., J. A. Atkins, J. F. Bader, D. J. Schafer, D. J. Patterson, T. W. Geary, and M. F. Smith. 2008. Effect of ovulatory follicle size and expression of estrus on progesterone secretion in beef cows. J. Anim. Sci. 86:553–563.[Abstract/Free Full Text]
Ciccioli, N. H., R. P. Wettemann, L. J. Spicer, C. A. Lents, F. J. White, and D. H. Keisler. 2003. Influence of body condition at calving and postpartum nutrition on endocrine function and reproductive performance of primiparous beef cows. J. Anim. Sci. 81:3107–3120.[Abstract/Free Full Text]
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National Animal Health Monitoring System. 1997 Part 1: Reference of 1997 beef cow-calf management practices. http://nahms.aphis.usda.gov/beefcowcalf/beef97/bf97pt1/pdf Accessed Oct. 24, 2007.
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Abstract
INTRODUCTION
