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Effect of Pretreatment with Prostaglandin F₂ Before Resynchronization of Ovulation on Fertility of Lactating Dairy Cows

E. Silva^*, R. A. Sterry^*, D. Kolb, M. C. Wiltbank^* and P. M. Fricke^*,1

^* Department of Dairy Science, University of Wisconsin, Madison 53706
Lodi Veterinary Clinic, Lodi, WI 53555

¹ Corresponding author: pmfricke{at}wisc.edu

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Our objective was to assess the effect of pretreatment with PGF₂ 12 d before initiation of a protocol for resynchronization of ovulation (Resynch) using an Ovsynch protocol. Lactating Holstein cows diagnosed not pregnant 31 d after a timed artificial insemination (TAI) were randomly assigned to initiate the Resynch protocol 32 d after TAI (n = 255; RES), or receive 25 mg of PGF₂ 34 d after TAI and initiate the Resynch protocol 12 d later at 46 d after TAI (n = 272; PGF+RES). Within each treatment, a subset of cows were examined using transrectal ultrasonography to determine ovulatory response to the first GnRH injection of the Resynch protocols or a blood sample was collected to determine serum progesterone (P₄) at initiation of the Resynch protocol, or both. Overall, PGF+RES cows had more pregnancies per artificial insemination (P/AI) than RES cows 66 d after TAI (35.2 vs. 25.6%), whereas pregnancy loss from 31 to 66 d after TAI was greater for RES than PGF+RES cows (17.1 vs. 7.6%). Although P/AI was greater for cows with high (1.0 ng/mL) vs. low (<1.0 ng/mL) P₄ at the first GnRH injection of the Resynch protocols, treatment did not affect the proportion of cows with low P₄ at the first GnRH injection of the Resynch protocols. Overall, no effect of treatment on ovulatory response to the first GnRH injection of the Resynch protocols was detected. We conclude that pretreatment with PGF₂ 12 d before initiation of the Resynch protocol increased P/AI 66 d after TAI for cows with serum P₄ concentration >1.0 ng/mL at the first GnRH injection of the Resynch protocol and decreased pregnancy loss from 31 to 66 d after TAI. This modified resynchronization protocol may be a useful strategy for reproductive management of lactating dairy cows.

Key Words: dairy cow • Resynch • fertility • pregnancy loss

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Use of Presynch (Moreira et al., 2001) and Ovsynch (Pursley et al., 1997a) protocols and timed artificial insemination (TAI) have dramatically improved service rate to first AI and reduced the negative impact of poor expression and detection of estrus on dairies. Systematic strategies to resynchronize cows failing to conceive to first postpartum TAI are only now beginning to be developed and evaluated. Conception rate to first postpartum TAI is around 35% (Pursley et al., 1997a,b; Fricke et al., 2003), resulting in a large proportion of nonpregnant cows that need to be resynchronized after their first postpartum TAI. Many dairy producers have used Ovsynch for resynchronizing ovulation (i.e., Re-synch) for cows diagnosed not pregnant to a previous TAI; however, the optimal timing of this strategy has not been well established.

One strategy used to increase conception rate to TAI after a Resynch protocol has been to choose intervals after TAI to initiate the Resynch protocol based on assumptions regarding the physiology of the estrous cycle (Fricke et al., 2003; Sterry et al., 2006a). Assuming an estrous cycle length of 21 to 24 d, initiation of a Resynch protocol 32 to 33 d after TAI should ensure that the first GnRH injection of the Resynch protocol is given between d 8 to 12 of the estrous cycle, a stage of the cycle when a corpus luteum (CL) should be present, resulting in greater conception rate when Ovsynch is initiated (Vasconcelos et al., 1999; Moreira et al., 2000). Despite this assumption, 16 to 22% of cows lacked a CL 33 d after TAI (Fricke et al., 2003; Sterry et al., 2006a) suggesting that there is significant variability in the stage of the estrous cycle, cyclicity status, or both, among cows 33 d after synchronization using Presynch + Ovsynch and TAI. Potential reasons for this variability among cows include normal variation among cows in length of the estrous cycle, the occurrence of pregnancy loss, lack of synchrony of ovarian function after the initial Presynch + Ovsynch protocol, or a combination of these.

Based on problems with the assumptions in the first approach, an alternative approach might be to presynchronize cows before initiation of the Resynch protocol. A common protocol to improve conception rate to Ov-synch at first postpartum TAI is to presynchronize groups of cows using 2 injections of PGF₂ administered 14 d apart with the second PGF₂ injection administered 12 to 14 d before the first GnRH injection of Ov-synch (Moreira et al., 2001; Navanukraw et al., 2004). After the second injection of PGF₂ of a Presynch + Ovsynch protocol, 90 to 95% of cyclic cows were detected in estrus within 7 d (Moreira et al., 2001). Thus, initiation of Ovsynch 12 d after treatment with PGF₂ would result in initiation of Ovsynch during the early to mid-luteal stages of the estrous cycle, thereby improving conception rate to TAI.

The objective of this study was to compare a commonly used resynchronization protocol initiated 32 d after TAI (RES) with a strategy in which cows were pretreated with a single injection of PGF₂ 12 d before initiation of the Resynch protocol (PGF+RES). Our hypothesis was that pretreatment with PGF₂ would increase the proportion of cows with a CL at initiation of the Resynch protocol and the likelihood that they would ovulate a follicle to the first GnRH injection of the Re-synch protocol, thereby improving conception rate to resynchronization of ovulation and TAI.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Farm Description and Data Collection
Lactating Holstein cows on a commercial dairy with 1,600 lactating cows located in south-central Wisconsin were enrolled into this study from September, 2005 to May, 2006. Cows were housed in free-stall barns and were milked thrice daily at approximately 8-h intervals. All cows received bST (Posilac, 500 mg, Monsanto Co., St. Louis, MO) beginning 57 to 70 d postpartum and continuing every 14 d throughout the study.

Cow lists for injection schedules, pregnancy examinations, and reproductive events for individual cows were generated, tracked, and recorded using a commercial on-farm computer software program (Dairy Comp 305, Valley Agricultural Software, Tulare, CA). Cows assigned to the study were identified and coded by treatment on the individual electronic card associated with each cow, and the cow file chronicling events for each cow was archived weekly to capture individual cow data throughout the study. Data from archived cow files were exported into a computer spreadsheet program (Excel 2002, Microsoft Corporation, Redmond, WA) for organization and manipulation of data before statistical analysis using SAS (2003).

Submission of Cows for First Postpartum TAI
Lactating Holstein cows (n = 843) with an average of 2.0 ± 1.2 lactations were enrolled into the study 1 wk before scheduled pregnancy diagnosis after receiving a hormonal synchronization protocol (Presynch + Ov-synch) using i.m. injections of 100 —g of GnRH (Cystorelin, Merial, Ltd., Duluth, GA) and 25 mg of PGF₂ (5 mL of Lutalyse, Pfizer Animal Health, New York, NY) as follows: PGF₂ (d 46 ± 3 and d 60 ± 3), GnRH (d 72 ± 3), PGF₂ (d 79 ± 3), GnRH 54 h after PGF₂ followed by TAI approximately 16 h later (d 82 ± 3 postpartum). A total of 7 of these cows were not submitted for pregnancy diagnosis because they either left the herd or missed their scheduled ultrasound examination.

Resynchronization Treatments
Pregnancy status was determined 31 d after Pre-synch + Ovsynch and TAI using a portable ultrasound scanner equipped with a 5 to 10 MHz linear-array transducer (Sonosite VET 180 plus, SonoSite Inc., Bothell, WA). The herd veterinarian, who had 8 yr experience using ultrasound for pregnancy diagnosis, conducted all pregnancy examinations 31 d after TAI throughout the experiment. Cows were blocked by parity (primiparous vs. multiparous) and were randomized and assigned to 1 of 2 resynchronization treatments for second and third postpartum TAI. Treatment codes for cows diagnosed pregnant were removed from the DC305 program so that they discontinued treatment, whereas cows diagnosed not pregnant continued the Resynch treatment.

Cows diagnosed not pregnant received Ovsynch for resynchronization of ovulation using i.m. injections of 100 µg of GnRH and 25 mg of PGF₂ and TAI as depicted in Figure 1. All cows received TAI approximately 16 h after the second GnRH injection of each resynchronization protocol. Cows enrolled in the first treatment (n = 255; RES) diagnosed not pregnant 31 d after TAI (Monday) received the first GnRH injection of the Resynch protocol 32 d after TAI (Tuesday), and this treatment was considered a control group. Cows enrolled in the second treatment (n = 272; PGF+RES) diagnosed not pregnant 31 d after TAI (Monday) received 25 mg of PGF₂ i.m. 34 d after TAI (Thursday) followed by the first GnRH injection of the Resynch protocol 12 d later at 46 d after TAI (Tuesday). In this way, all hormonal injections associated with synchronization and resynchronization protocols were restricted to 2 d of the week (Tuesdays and Thursdays) with pregnancy diagnoses occurring on Mondays and TAI occurring on Fridays. Cows failing to conceive to the first Resynch TAI remained in the same treatment group for a second Re-synch TAI.

View larger version (10K): [in this window] [in a new window]   Figure 1. Schematic diagram of the timing and sequence of injections for the resynchronization of ovulation protocols. Cows diagnosed not pregnant 31 d after timed AI (TAI) using ultrasound (US) were assigned randomly to receive the first GnRH injection of the resynchronization protocol 32 d (RES) after a previous TAI or were pretreated with prostaglandin F2 (PGF) 12 d before receiving the first GnRH injection of the resynchronization protocol (PGF+RES).

Blood Sampling and Progesterone Analysis
Blood samples for analysis of serum progesterone (P₄) concentration were collected via venipuncture of the median caudal vein or artery into evacuated tubes (Vacutainer, BD, Franklin Lakes, NJ) at the first GnRH injection of each Resynch treatment of a subset of cows in both treatments (251 RES and 253 PGF+RES cows). Blood samples were allowed to clot for 12 h at 4°C, centrifuged (1,935 x g for 15 min), and serum was harvested and stored at –20°C until assayed for P4 concentration using a solid-phase, no-extraction radioimmunoassay (Coat-a-Count, Diagnostic Products Corp., Los Angeles, CA). Intraassay and interassay coefficients of variation were 8.0 and 3.6%, respectively.

Ovarian Ultrasonography
Transrectal ultrasonography was conducted in a subgroup of cows (152 RES and 130 PGF+RES cows) using a portable scanner (Easiscan, BCF Technology Ltd., Livingston, UK) fitted with a 7.5-MHz linear-array transducer to determine the ovarian structures at the first GnRH injection of the Resynch protocols and 7 d later at the PGF₂ injection. Diameter of the follicle and CL was estimated using on-screen background gridlines comprising squares with 10-mm sides as described previously (Rivera et al., 2006). Ovulation was defined as the presence of a follicle on the day of first ultrasound examination and presence of a CL in the same location of the ovary 7 d later at the second ultrasound examination. Because of missing data at the first GnRH injection or at PGF₂ injections, 25 cows were excluded from this analysis.

Statistical Analyses
Dichotomous data were analyzed using the Logistic procedure of SAS (2003). A multivariate logistical regression model was developed to analyze the effect of the categorical variables treatment (RES vs. PGF+RES), parity (primiparous vs. multiparous), re-synch number (first vs. second), and all 2-way interactions of the explanatory variables with treatment on P/ AI at 31 and 66 d after TAI and pregnancy loss.

The same multivariate logistical regression model was used for the analysis of the subgroup of cows that were examined with ultrasound at the first GnRH and PGF₂ injections of the Resynch protocols. The effect of treatment, Resynch number, and P₄ (<1.0 ng/mL vs. 1.0 ng/mL) on ovulatory response after the first GnRH injection of the Resynch protocols and the effect of treatment, ovulation after the first GnRH injection of the Resynch protocols, and presence of a CL at the PGF₂ injection of the Resynch protocols on P/AI 31 and 66 d after TAI were evaluated. Interaction of the explanatory variables with treatment was included in both statistical models. Because a total of 94 cows had missing blood samples thereby comprising a distinct subgroup of cows, a separate statistical model was developed to analyze the effect of treatment, low vs. high P₄ (<1.0 ng/mL vs. 1.0 ng/mL), and the interaction of treatment and P₄ class on P/AI 31 and 66 d after TAI and pregnancy loss.

All multivariate logistical regression models were constructed using a backward selection procedure with treatment retained as a fixed effect in each of the models. A Wald statistic criterion of P < 0.15 was set for including variables in the statistical model. Treatment differences with P < 0.05 were considered significant, and differences between P > 0.05 and P < 0.15 were considered statistical tendencies. Data are presented as percentages and proportions with P-values for main effects and interactions derived from the multivariate logistical regression analysis.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Of the 843 cows enrolled into the study, 7 cows were not submitted for pregnancy diagnosis after Presynch + Ovsynch TAI because they either left the herd or missed their scheduled ultrasound examination. After exclusion of these 7 cows, P/AI 31 d after the Presynch + Ovsynch protocol was 37.0% (309/836) and was similar between primiparous 35.3% (120/340) and multiparous 38.1% (189/496) cows. By design, mean DIM at pregnancy diagnosis after the Presynch + Ovsynch protocol was similar (P > 0.1) between RES and PGF+RES cows (111.8 ± 0.3 vs. 112.0 ± 0.2, respectively).

After exclusion of cows diagnosed pregnant 31 d after first postpartum TAI (Table 1), a total of 527 nonpregnant cows remained in the study to receive RES (n = 255) and PGF+RES (n = 272) treatments. One hundred eleven cows enrolled in the study and diagnosed not pregnant at 31 d after first TAI did not complete the resynchronization protocol for the reasons described in Table 1. For the final analysis, a total of 198 cows were included in the RES treatment and 218 cows were included in the PGF+RES treatment of first resynchronization of ovulation. At the subsequent TAI, 43 and 35 cows were excluded from the RES and PGF+RES treatments, respectively resulting in 88 RES and 94 PGF+RES cows included in the final analysis for second resynchronization of ovulation (Table 1).

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One possible explanation for the reduced pregnancy loss for PGF+RES cows is that pretreatment with PGF₂ before the Resynch protocol may have had a direct beneficial effect on the uterine environment for cows undergoing early pregnancy loss after the preceding TAI. Pregnancy loss is more frequent before maternal recognition of pregnancy (d 16 to 19 of the estrous cycle; Santos et al., 2004). In addition, a positive effect of treatment with PGF₂ to synchronize estrous behavior on conception rate has been reported in cattle (Roche, 1976; Macmillan and Day, 1982).

Taken together, the improvement in P/AI by pretreatment with PGF₂ has potential to improve reproductive performance on dairies that use a systematic synchronization and resynchronization approach for reproductive management. In addition, overall P/AI 31 d after TAI for PGF+RES cows (38.5%) was similar to that of cows submitted to first postpartum TAI after a Presynch + Ovsynch protocol (37.0%). Thus, the proportion of less fertile cows does not necessarily increase with each TAI attempt, but rather a reduction in synchrony of ovulation at second and greater TAI may account for most of this reduction in fertility. Thus, the similarity between conception rates at the first and subsequent TAI also suggests better resynchronization of ovulation with the PGF+RES treatment.

Role of Progesterone Concentration at Initiation of the Resynch Protocols
A key hypothesis of the present study was that pre-treatment with PGF₂ 12 d before initiation of the Re-synch protocol would increase the number of cows with high P₄ at initiation of the Resynch protocol. When resynchronization of ovulation was initiated 33 d after TAI, cows with a CL at the first GnRH injection tended to have more P/AI than cows lacking a CL (Fricke et al., 2003), and a similar effect was reported for cows receiving a Presynch + Ovsynch protocol (Sterry et al., 2006b). Cows with low P4 should be at either late or early stages of the estrous cycle or may represent a population of anovular cows. When an Ovsynch protocol is initiated at these stages of the estrous cycle or in anovular cows, a reduction in conception rate to TAI has been reported (Vasconcelos et al., 1999; Gmen et al., 2003; Sterry et al., 2006b).

To evaluate the effect of serum P₄ at initiation of the Resynch protocol on P/AI, cows were classified by serum P₄ at the first GnRH injection of the Resynch protocols as either low (<1.0 ng/mL) or high (1.0 ng/mL) as described previously (Rivera et al., 2005). Overall, the proportion of cows with high P₄ at the first GnRH injection of the Resynch protocol did not differ (P > 0.10) between RES (n = 251, 76.1%) or PGF+RES (n = 253, 73.1%) cows. It is surprising that a similar percentage of cows in both treatments lacked a functional CL at initiation of the Resynch protocols especially because PGF+RES cows were treated with PGF₂ 12 d before the first GnRH injection. El-Zarkouny et al. (2004) reported that presynchronization with 2 injections of PGF₂ increased the proportion of cows with high P₄ (1.0 ng/mL) at the first GnRH injection of Ovsynch by 13 percentage points. By contrast, Moreira et al. (2001) did not observe an effect of a similar presynchronization protocol on the proportion of cyclic cows with high P₄ at the first GnRH injection of Ovsynch, although they did report that presynchronized cows had greater P₄ concentrations at the PGF₂ injection 7 d later. Nonetheless, the proportion of cows with low P₄ in the present study is similar to the 16 and 22% of cows reported to lack a CL at the first GnRH injection of a Resynch protocol (Fricke et al., 2003; Sterry et al., 2006a) and may support the observation that these cows were anovular at initiation of the Resynch protocols. Although results from these 2 methodologies (serum P₄ vs. ultrasound) are not perfectly correlated, the statistical agreement (kappa) between the presence or absence of a CL using transrectal ultrasonography and serum P₄ concentration at the ultrasound examination was 0.74, indicating a high level of agreement between these methods (Silva et al., 2007).

When the variable P₄ concentration at the first GnRH injection of the Resynch protocols was included in the statistical model to assess the effect of treatment and P₄ status on P/AI 31 and 66 d after TAI, cows with low P₄ at the first GnRH injection of the Resynch protocols had fewer P/AI at 31 (P < 0.008) and 66 (P < 0.005) d after TAI than cows with high P₄ regardless of resynchronization treatment (Table 4). Although this outcome was expected, the overall data on circulating progesterone from the present study did not provide a clear explanation for the improvement in P/AI observed for the PGF+RES treatment. Cows from the RES and PGF+RES treatments that had low P₄ at the first GnRH injection of the Resynch protocols (25% of cows; Table 4) had low P/AI after the Resynch TAI, whereas the effect of pretreatment with PGF₂ on P/AI in the present study was only observed for cows with high P₄ at initiation of the Resynch protocols. An intriguing possibility to explain the lack of an effect of pretreatment with PGF₂ on the proportion of cows with low P₄ in the present study is that a proportion of cows are anovular at this time despite completing a synchronization protocol earlier postpartum; however, further research is needed to either confirm or refute this explanation.

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View this table: [in this window] [in a new window]   Table 5. Effect of treatment and progesterone (P4) concentration (high vs. low)1 at the first GnRH injection of the Resynch protocols on ovulatory response of lactating Holstein cows for all cows and for cows in which the largest follicle was 10 mm2

View this table: [in this window] [in a new window]   Table 6. Effect of treatment and ovulatory response (yes vs. no) after the first GnRH injection of the Resynch protocols on pregnancies per AI (P/AI) 66 d after timed AI (TAI) in lactating Holstein cows for all cows and for cows in which the largest follicle was 10 mm1

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	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Coupling a nonpregnancy diagnosis with a management decision to quickly reinseminate cows may improve reproductive efficiency by decreasing the interval between AI services. By contrast, early pregnancy loss and the effectiveness of resynchronization protocols initiated at different stages after a previous TAI may limit the effectiveness of resynchronization strategies. In the present study, PGF+RES cows had more P/AI 66 d after TAI compared with RES cows and less pregnancy loss from 31 to 66 d after TAI. It is unclear whether the improvement in P/AI observed for PGF+RES cows in the present study can compensate for the greater interval (14 d) between AI services. Based on pregnancy outcomes 66 d after TAI, pretreatment with PGF₂ 12 before initiation of the Resynch protocol yielded a 9.6 percentage point increase in P/AI compared with the control treatment or about 37.5% more pregnancies at each Resynch AI (9.6/25.6 = 37.5%). A comparison of the economic value of these protocols on dairy farms is complex and will require further research with a larger number of farms with differences in management practices, milk production, and lactation persistency in the economic models. Nonetheless, data from the present study support the concept that P/AI to TAI after resynchronization of ovulation can achieve a similar rate to that observed after a Presynch + Ovsynch protocol for first postpartum TAI. Future studies to confirm these results and investigate other methods for presynchronizing cows to improve P/AI to resynchronization of ovulation are warranted.

	ACKNOWLEDGEMENTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
The authors thank Blue Star Dairy, De Forest, WI, and their staff for the use of their cows and facilities for this study.

Received for publication April 25, 2007. Accepted for publication August 21, 2007.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 


Ahmad, N., F. N. Schrick, R. L. Butcher, and E. K. Inskeep. 1995. Effect of persistent follicles on early embryonic losses in beef cows. Biol. Reprod. 52:1129–1135.[Abstract]

Bartolome, J. A., F. T. Silvestre, S. Kamimura, A. C. M. Arteche, P. Melendez, D. Kelbert, J. McHale, K. Swift, L. F. Archbald, and W. W. Thatcher. 2005a. Resynchronization of ovulation and timed insemination in lactating dairy cows I: Use of the Ovsynch and Heatsynch protocols after non-pregnancy diagnosis by ultrasonography. Theriogenology 63:1617–1627.[CrossRef][Medline]

Bartolome, J. A., A. Sozzi, J. McHale, K. Swift, D. Kelbert, L. F. Archbald, and W. W. Thatcher. 2005b. Resynchronization of ovulation and timed insemination in lactating dairy cows: III. Administration of GnRH 23 days post AI and ultrasonography for non-pregnancy diagnosis on day 30. Theriogenology 63:1643–1658.[CrossRef][Medline]

Cerri, R. L. A., H. M. Rutigliano, R. G. S. Bruno, R. C. Chebel, and J. E. P. Santos. 2005. Effect of artificial insemination (AI) protocol on fertilization and embryo quality in high producing dairy cows. J. Dairy Sci. 88(Suppl.1):86. (Abstr.)[Abstract/Free Full Text]

Chebel, R. C., J. E. P. Santos, R. L. A. Cerri, H. M. Rutigliano, and R. G. S. Bruno. 2006. Reproduction in dairy cows following progesterone insert presynchronization and resynchronization protocols. J. Dairy Sci. 89:4205–4219.[Abstract/Free Full Text]

El-Zarkouny, S. Z., J. A. Cartmill, B. A. Hensley, and J. S. Stevenson. 2004. Pregnancy in dairy cows after synchronized ovulation regimens with or without presynchronization and progesterone. J. Dairy Sci. 87:1024–1037.[Abstract/Free Full Text]

Fricke, P. M., D. Z. Caraviello, K. A. Weigel, and M. L. Welle. 2003. Fertility of dairy cows after resynchronization of ovulation at three intervals following first timed insemination. J. Dairy Sci. 86:3941–3950.[Abstract/Free Full Text]

Gümen, A., J. N. Guenther, and M. C. Wiltbank. 2003. Follicular size and response to Ovsynch versus detection of estrus in anovular and ovular lactating dairy cows. J. Dairy Sci. 86:3184–3194.[Abstract/Free Full Text]

Macmillan, K. L., and A. M. Day. 1982. Prostaglandin F₂—Fertility drug in dairy cattle. Theriogenology 18:245–253.[CrossRef][Medline]

Mihm, M., A. Baguisi, M. P. Boland, and J. F. Roche. 1994. Association between the duration of dominance of the ovulatory follicle and pregnancy rate in beef heifers. J. Reprod. Fertil. 102:123–130.[Abstract/Free Full Text]

Moreira, F., R. L. de la Sota, T. Diaz, and W. W. Thatcher. 2000. Effect of day of estrous cycle at the initiation of a timed artificial insemination protocol on reproductive responses in dairy heifers. J. Anim. Sci. 78:1568–1576.[Abstract/Free Full Text]

Moreira, F., C. Orlandi, C. A. Risco, R. Mattos, F. Lopes, and W. W. Thatcher. 2001. Effects of presynchronization and bovine somatotropin on pregnancy rates to a timed artificial insemination protocol in lactating dairy cows. J. Dairy Sci. 84:1646–1659.[Abstract]

Navanukraw, C., D. A. Redmer, L. P. Reynolds, J. D. Kirsch, A. T. Grazul-Bilska, and P. M. Fricke. 2004. A modified presynchronization protocol improves fertility to timed artificial insemination in lactating dairy cows. J. Dairy Sci. 87:1551–1557.[Abstract/Free Full Text]

Perry, G. A., M. F. Smith, M. C. Lucy, J. A. Green, T. E. Parks, M. D. MacNeil, A. J. Roberts, and T. W. Geary. 2005. Relationship between follicle size at insemination and pregnancy success. Proc. Natl. Acad. Sci. USA 102:5268–5273.[Abstract/Free Full Text]

Pursley, J. R., M. R. Kosorok, and M. C. Wiltbank. 1997a. Reproductive management of lactating dairy cows using synchronization of ovulation. J. Dairy Sci. 80:301–306.[Abstract]

Pursley, J. R., M. C. Wiltbank, J. S. Stevenson, J. S. Ottobre, H. A. Garverick, and L. L. Anderson. 1997b. Pregnancy rates per artificial insemination for cows and heifers inseminated at a synchronized ovulation or synchronized estrus. J. Dairy Sci. 80:295–300.[Abstract]

Rivera, H., H. Lopez, and P. M. Fricke. 2005. Use of intravaginal progesterone-releasing inserts in a synchronization protocol before timed AI and for synchronizing return to estrus in Holstein heifers. J. Dairy Sci. 88:957–968.[Abstract/Free Full Text]

Rivera, H., R. A. Sterry, and P. M. Fricke. 2006. Presynchronization with gonadotropin-releasing hormone does not improve fertility in Holstein heifers. J. Dairy Sci. 89:3810–3816.[Abstract/Free Full Text]

Roche, J. F. 1976. Fertility in cows after treatment with a prostaglan-din analogue with or without progesterone. J. Reprod. Fertil. 46:341–345.[Abstract/Free Full Text]

Santos, J. E., W. W. Thatcher, R. C. Chebel, R. L. Cerri, and K. N. Galvao. 2004. The effect of embryonic death rates in cattle on the efficacy of estrus synchronization programs. Anim. Reprod. Sci. 82–83:513–535.

Sartori, R., P. M. Fricke, J. C. P. Ferreira, O. J. Ginther, and M. C. Wiltbank. 2001. Follicular deviation and acquisition of ovulatory capacity in bovine follicles. Biol. Reprod. 65:1403–1409.[Abstract/Free Full Text]

SAS Institute. 2003. SAS 9.1, Version 3. SAS Institute Inc., Cary, NC.

Silva, E. P. B., R. A. Sterry, and P. M. Fricke. 2007. Assessment of a practical method for identifying anovular lactating dairy cows synchronized for first postpartum timed artificial insemination. J. Dairy Sci. 90:3255–3262.[Abstract/Free Full Text]

Sterry, R. A., P. W. Jardon, and P. M. Fricke. 2007. Effect of timing of Cosynch on fertility of lactating Holstein cows after first postpartum and Resynch timed AI services. Theriogenology 67:1211–1216.[CrossRef][Medline]

Sterry, R. A., M. L. Welle, and P. M. Fricke. 2006a. Effect of interval from timed artificial insemination to initiation of resynchronization of ovulation on fertility of lactating dairy cows. J. Dairy Sci. 89:2099–2109.[Abstract/Free Full Text]

Sterry, R. A., M. L. Welle, and P. M. Fricke. 2006b. Treatment with gonadotropin-releasing hormone after first timed artificial insemination improves fertility in noncycling lactating dairy cows. J. Dairy Sci. 89:4237–4245.[Abstract/Free Full Text]

Vasconcelos, J. L. M., R. W. Silcox, G. J. M. Rosa, J. R. Pursley, and M. C. Wiltbank. 1999. Synchronization rate, size of ovulatory follicle, and pregnancy rate after synchronization of ovulation beginning on different days of the estrous cycle in lactating dairy cows. Theriogenology 52:1067–1078.[CrossRef][Medline]

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