Effect of Treatment with Additional Doses of Prostaglandin F2 Alpha during the Middle Stage of the Oestrus Cycle on Luteolysis Process and Reproduction Performance in Holstein Dairy Cows

Iranian Journal of Applied Animal Science

مقاله 6، دوره 12، شماره 3، آذر 2022، صفحه 471-478   

نوع مقاله: Research Articles

نویسندگان

N. Neisari¹؛ A. Kaveh²؛ P. Pooladzadeh³؛ A. Hajibemani^{* 4}؛ F. Mirzaeei⁵

¹Department of Theriogenology, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran

²Department of Clinical Science, Faculty of Veterinary Medicine, Tabriz Branch, Islamic Azad University, Tabriz, Iran

³Department of Clinical Science, Karaj Branch, Islamic Azad University, Karaj, Iran

⁴Department of Clinical Science, Faculty of Veterinary Medicine, University of Tabriz, Tabriz, Iran

⁵Department of Medicine, Qazvin University of Medical Science, Qazvin, Iran

چکیده

For the manipulation of the oestrus cycle, the prostaglandin F₂ alpha (PGF₂α) is a commonly used strategy in dairy cows. The objective of the study was to evaluate the luteolysis response and reproductive performance after treatment with one or two injections of PGF₂α. A total of 84 Holstein dairy cows, being in the middle stage of the oestrus cycle (between days 7 and 12) were enrolled in a completely randomized design and divided into three groups: group 1 (n=30), received a single dose of PGF₂α injection, whereas, group 2 (n=24) and group 3 (n=30), were treated with two doses of PGF₂α injections at 12 and 24 hours intervals, respectively. The corpus luteum diameter was measured using the ultrasound at the beginning, 24, 48 and 72 hours after PGF₂α injection. Blood samples were collected to assess progesterone (P₄) on day 0 and 72 hours after treatment. Oestrus expression, PGF₂α-oestrus interval and first service conception rate were evaluated. The results showed that the luteolysis process, the mean of PGF₂α-oestrus interval and progesterone concentration at the beginning (day 0) and 72 hours after treatment were similar for all the groups. Oestrus expression (PGF₂α+PGF₂α-24 h=76.7% vs. PGF₂α+PGF₂α-12 h=66.7% and control=56.7%, P>0.05) and the first service conception rate (PGF₂α+PGF₂α-24 h=41.2% vs. PGF₂α+PGF₂α-12 h=40.0% and control=33.3%, P>0.05) were relatively higher in cows receiving two doses of PGF₂α injections at 24-hour-interval (P>0.05). In conclusion, treatment with an additional dose of PGF₂α during the middle stages of the oestrus cycle has no significant effect on luteolysis or reproductive performance.

کلیدواژه‌ها

dairy cows؛ luteolysis؛ PGF2α؛ reproduction performance

اصل مقاله

INTRODUCTION

Because of the increased milk production, the duration of oestrus decreases (Lopez et al. 2004; Wiltbank et al. 2006) and the current detection rate of oestrus is generally not optimal for efficient reproductive management programs in dairy farms (Senger, 1994; Peralta et al. 2005). In this regard, conception rates to the first insemination have been decreasing (Washburn et al. 2002). Hormonal treatment using prostaglandin F₂ alpha (PGF₂α) to manipulate the oestrus cycle is a commonly used strategy in dairy farms (Ahuja et al. 2005). It is a well-known concept that if cows do not become pregnant, PGF₂α is produced by uterine glands at the end of the luteal phase, which triggers luteolysis and initiates a new oestrus cycle (Schams and Berisha, 2004; Ginther et al. 2009). Luteolysis can be induced pharmacologically in cows during the diestrus phase (Wenzinger and Bleul, 2012). But, the newly formed corpus luteum (CL) is resistant to induction of luteolysis by exogenous PGF₂α until day 5 of the oestrus cycle (Levy et al. 2000). Devising new synchronisation procedures to promote reproductive efficiency in dairy industry has aroused considerable research interest within the past decade (Wiltbank and Pursley, 2014). Artificial shortening of the oestrus cycle after a PGF₂α treatment is likely to influence follicle selection, subsequent ovulation, or the development of a functional CL in the dairy cows (Schams and Berisha, 2004). PGF₂α has been used in many synchronisation protocols, such as OV-Synch, CO-Synch, Heat-Synch, CO-Synch‏-controlled internal drug release (CIDR), etc. Previous studies have indicated that incomplete luteal regression occurs in some cows are treated with synchronisation protocols (Moreira et al. 2000). CL regression rates induced by PGF₂α vary among different studies ranging from 81% to 95% (Pursley et al. 1997; Moreira et al. 2000; Gümen et al. 2003). Additionally, other studies have reported various percentages of cows with low progesterone (P₄) ranging from 84% to 94%, 48 h following PGF₂α administration (Cartmill et al. 2001; El-Zarkouny et al. 2004; Souza et al. 2007). Therefore, synchronisation protocols can be undermined due to the absence of a full luteal regression of CL after the administration of a single PGF₂α dose. Several research groups are working on devising practical procedures to induce luteolysis of CL during timed AI protocols, including: the injection of a single large dose PGF₂α (Ribeiro et al. 2012; Giordano et al. 2013) or two fractioned doses of PGF₂α administered at varying intervals (Brusveen et al. 2009; Ribeiro et al. 2012). Brusveen et al. (2009) observed that cows treated with two doses of PGF₂α during an OV-Synch protocol, had low P4 at the timed artificial insemination (TAI (compared to cows treated with a single PGF₂α dose (97.5 vs. 86.1%). These results were consistent with those of Wiltbank et al. (2015), who employed an additional dose of PGF₂α in the original OV-Synch and double OV-Synch. Moreover, they observed a trend towards increasing pregnancies per AI (P/AI( in cows treated with two doses of PGF₂α. The second dose of PGF₂α administered 24 h after the first one could reduce the P₄ at TAI, and thus increase P/AI in cows re-synchronised with G6G-Ovsynch protocol (Carvalho et al. 2015). Santos et al. (2010) and Ribeiro et al. (2012) used the same idea to shift back the PGF₂α from day 7 to day 5 and add a further dose on day 6 in the CO-Synch 72 h protocol to completely regress CL, particularly in pre-synchronised cows which have a high ovulation rate in response to the first GnRH and interestingly, both groups could improve fertility parameters. Previous reports described the ovulation time in cows treated with a single or two consecutive standard doses of PGF₂α followed by various synchronisation protocols (Santos et al. 2010; Ribeiro et al. 2012). However, details of the luteolysis process following the administration of single or two doses of PGF₂α at 12 and 24-hour intervals have not yet unravelled in such circumstances. Therefore, the present study was designed to evaluate the luteolysis response of mature CL during the middle stage of the unravel cycle after the administration of a single or two doses of PGF₂α at 12 and 24-hour intervals. Additionally, the pregnancy per AI was compared between different administration strategies.

 

MATERIALS AND METHODS

All procedures used in the present study were licensed by the Research Committee of the Faculty of Veterinary Medicine, Tabriz Branch, Islamic Azad University, Tabriz, Iran (Research Committee No: 10210501942028).

 

Animals

The current study was carried out on a dairy farm under the standard management in Ardabil province, located in the North-Western of Iran (1351 m above sea level; 38.2 N˚ 48.3 E˚). The herd consisted of 2000 Holstein dairy cows, housed in open shed barns and fed formulated diets. The diets were a mixture of alfalfa hay, corn silage, soybean meal, whole cottonseed, corn or milo grain, corn gluten feed, vitamins, and minerals. The cows were milked by a pipeline milking machine, three times a day. The voluntary waiting period of the herd was 45 days. Experienced personnel performed heat detection during the day. Estrus detection was performed by visual observation (6 times daily (during the night and day) for at least 20-30 minutes each) and inseminations were conducted based on the am/pm rule.

 

Treatments

A total of 84 registered Holstein dairy cows were enrolled. The animals had a mean of 75 days in milk (DIM) without a history of peripartum diseases (dystocia, retained placenta, clinical hypocalcemia and ketosis), mastitis, lameness and systemic diseases in the previous lactation. Body condition score (BCS) was recorded at the treatment course (based on a 1 to 5 score), which ranged between 2.75 and 3.5 (average=2.97±0.37) for the enrolled cows. The average milk production and parity of the cows were 31 kg per day and 2.01, respectively. The animals were randomly divided into three groups: group 1 (n=30), cows were intramuscularly (i.m) injected a single dose of 225 μg d-Cloprostenol (Gestavet Prost^®, Laboratorios, Hipra); Group 2 (n=24), cows were injected two doses of 225 μg d-Cloprostenol with 12–hour interval; group 3 (n=30), cows were injected two doses of 225 μg d-Cloprostenol with 24-hour interval. There was no significant difference among the groups in terms of the DIM.

 

Ovarian transrectal ultrasonography

Transrectal ultrasonography (US) examinations (Hitachi^®, Universal Medical System, Japan with a 7.5 MHz linear array transducer) of the ovaries were performed to assure that all the cows were within the middle stage of the estrous cycle (between days 7 and 12) and had a mature and functional CL (>17 mm) before the PGF₂α injection (Pieterse et al. 1990; Kayacik et al. 2006; Ginther, 2007). The CL diameter was evaluated using the US at the beginning, 24, 48 and 72 hours after the treatment. Following the observation of the maximum CL diameter in the images, the longitudinal and transversal diameters of the CL were measured at right angles with electronic callipers (Pierson and Ginther, 1984).

 

Progesterone assay

Blood samples were taken on day 0 and at 72 hours after the treatment via puncture of the median caudal vein with 8-mL evacuated tubes. Serum samples were separated from the blood specimens by centrifugation (750 g) at 4 ˚C for 15 minutes and stored at -20 ˚C until analysis. Progesterone concentrations were determined in duplicate using a commercial solid-phase, no-extraction radioimmunoassay (Coat-a-Count^®; Diagnostic Products Corp., Los Angeles, CA, USA). All the samples were evaluated in a single assay with quality control samples of high (18 ng/mL), medium (4 ng/mL), and low (0.5 ng/mL) concentrations of P₄ evaluated. The calculated sensitivity was 0.005 ng/mL with an intra-assay coefficients of variation (CV) of 5.9%.

 

Evaluation of reproductive performance

Heat detection was performed 4 times a day for 6 days after the treatment, and then inseminations were performed. The proportion of animals expressing oestrus and PGF₂α-oestrus interval was evaluated in all the groups. The first service conception rate was diagnosed and confirmed 30 days after the insemination by the US, based on the visualisation of an embryonic vesicle with a heartbeat, as described previously (Romano et al. 2006).

 

Statistical analysis

The SPSS software (Version 20.0, SPSS Inc., Chicago, Illinois) was employed for data analysis (SPSS, 2011). One-way ANOVA was used for comparison of different variables between the groups and post-hoc Tukey's test was used for significance. Oestrus rate and first service conception rate of different groups were analysed using the Chi-squared test. Effects of parity, milk production level and DIM on the first service conception rate were analysed using the multivariate logistic regression. Data were presented as the percentage or mean (±SD) and values of p ≤ 0.05 were considered as statistically significant.

 

RESULTS AND DISCUSSION

The mean percentage of CL regression was 85.4%, 3 days after treatment. The mean percentage of CL regression was 86.7, 87.0 and 82.8%, 3 days after PGF₂α treatment for cows received single PGF₂α treatment and cows received two PGF₂α doses at 12 and 24 hours intervals, respectively. The luteolysis process following PGF₂α administration was similar for the cows treated with single dose of PGF₂α and the cows received two doses at 12 and 24-hour intervals (P>0.05). No significant difference was observed among the groups regarding the CL size at the 24, 48 and 72 hours after the treatment (P>0.05) (Figure 1). A lack of new ovulation was also observed.

 

Figure 1 The CL diameter (Mean±SD) of treatment groups at the 0, 24, 48 and 72 hours after the treatment

 

The mean concentration of progesterone before (day 0) and 3 days after the treatment were 4.82 ± 0.15 and 0.76 ± 0.03 ng mL^-1, respectively, for all the cows. The concentration of progesterone was 0.74 ± 0.23, 0.75 ± 0.26 and 0.76 ± 0.39 in the single PGF₂α dose and two doses of PGF₂α administered 12 and 24 h apart, respectively, on day 3. However, the mean concentration of progesterone among treated groups was similar (P>0.05) at different days of sampling (Table 1). The data revealed that, 56.7% of animals were in oestrus after the injection of a single dose of PGF₂α. however, the repeated injections (two doses) at 12 and 24-hour intervals induced estrus in a proportion of 66.7% and 76.7% cows, respectively, with non-significant differences. The mean PGF₂α-oestrus interval was 3.35 ± 0.49, 3.37 ± 0.71 and 3.73 ± 0.61 in the single PGF₂α dose and two doses of PGF₂α administered 12 and 24 h apart, respectively.

 

Table 1 Concentrations of progesterone (ng mL-1) (Mean±SD) of the treatment groups at the beginning (day 0) and 3 days (day 3) after PGF₂α treatment

 

The mean PGF₂α-oestrus interval after the treatment was similar (P>0.05) for the cows who received the single dose of PGF₂α treatment or two doses at 12 and 24-hour intervals (Figure 2).

 

Figure 2 The mean PGF₂α-oestrus interval (Mean±SD) of treatment groups

 

The first service conception rate was presented in Figure 3.

 

Figure 3 First service conception rate of treatment groups

 

The P/AI was 33.3, 40.0 and 42.2% in the single PGF₂α dose and two doses of PGF₂α administered 12 and 24 h apart, respectively. The second PGF₂α treatment had no significant effect on P/AI in cows. The first service conception rate among the groups was not significantly different (P>0.05). However, the first service conception rate was numerically higher in cows treated with an additional dose of PGF₂α at 24-hour intervals. The parity, milk production level and DIM of cows were 2.1 ± 0.99, 1.7 ± 0.92 and 2.2 ± 1.47 and 31.01 ± 7.89, 28.0 ± 6.09 and 34.9 ± 8.50 and 73.63 ± 17.90, 75.41 ± 18.92 and 73.50 ± 17.59 in the single PGF₂α dose and two doses of PGF₂α administered 12 and 24 h apart, respectively. The parity, milk production level and DIM of cows do not affect the first service conception rate (P>0.05). Moreover, milk production on the day of treatment had no relationship with the interval to oestrus after treatment. No possible stress associated with milk yield appeared to influence the luteolysis process, the proportion of animals expressing oestrus and interval to oestrus following PGF₂α administration. The current study evaluated whether the injection of two consecutive doses of PGF₂α at 12 and 24-hour intervals would promote the luteolysis process of mature and functional CL as well as reproductive performance during the middle stage of the oestrus cycle in dairy cows. The previous studies reported lower fertility in cows that had not complete luteal regression after the PGF₂α treatment in the OV-Synch protocol (Giordano et al. 2012b; Giordano et al. 2013). An acceptable luteal regression is needed around the AI to decrease P₄ concentrations and adequately optimise fertility (Ribeiro et al. 2012). Numerous studies demonstrated that in OV-Synch-type protocols, in which a single dose of PGF₂α is used, 10 to 25% of cows have inadequate regression of the CL (Giordano et al. 2012b). Therefore, several studies are currently being conducted to increase the effects of PGF₂α administration during synchronisation protocols for complete regression of CL. The present study showed that a single dose intra-muscular injection of PGF₂α was equally effective to those of 2 injections. The luteolysis process was similar between the cows treated with a single dose of PGF₂α and those treated with two doses of PGF₂α 12 and 24-hour intervals. No difference was observed among the groups regarding the CL size at different sampling days. Moreover the CL regression rate was 97.0% and 83.0% in animals treated with the two doses and a single dose of PGF₂α during the OV-Synch protocol (Wiltbank et al. 2015). The experiments revealed that the addition of a second PGF₂α injection could increase the rate of luteal regression and result in lower P₄ concentrations at a final GnRH of the OV-Synch protocol (Carvalho et al. 2015; Barletta et al. 2018). The second PGF₂α treatment 24 h increased the percentage of cows with low P4 concentration (≤0.5 ng/mL) at the second GnRH treatment of the OV-Synch protocol compared to the control group (73.2% vs. 55.7% P< 0.01) (Tippenhauer et al. 2021). The addition of PGF₂α injection during the Ovsynch protocol increased +11.6 percentage units luteal regression (Borchardt et al. 2018). On the contrary, other studies have claimed that there is no need for an injection of PGF₂α at two separate times, which is consistent with the results of this study (Santos et al. 2010; Giordano et al. 2012a; Atanasov et al. 2021). For example, it has been reported that the complete CL regression rate was between 73.9 to 95.2% following a single dose treatment with different types of PGF₂α analogues in lactating dairy cows and there was no significant difference between the groups (Santos et al. 2010; Giordano et al. 2012a; Atanasov et al. 2021). In our study, the mean percentage of CL regression was 85.4%, 3 days after treatment. The mean percentage of CL regression was 86.7, 87.0 and 82.8%, 3 days after PGF₂α treatment for cows received single PGF₂α treatment and cows received two PGF₂α doses at 12 and 24 hours intervals, respectively. The percentage of heifers that had regressed CL after 1 or 2 injections of PGF₂α was 86.9 and 92.8%, respectively, when utilising the 5-day CO-Synch + CIDR protocol in dairy heifers. Consistently, no significant difference was observed between various groups regarding the percentages of luteolysis (Rabaglino et al. 2010). Luteal regression in cows with a functional CL was greater for multiparous cows receiving the 750 mg dose of PGF₂α compared to those receiving the 500 mg dose under breeding-OV-Synch. However, it has been reported that the greater dose of PGF₂α did not increase the percentage of primiparous cows with luteal regression during Double-OV-Synch (Giordano et al. 2013). Consistently, Say et al. (2016) demonstrated that there was no difference in CL regression between a single (25 mg) vs. double injection of PGF₂α (50 mg) in dairy heifers. The percentage of cows with complete luteal regression did not differ among double PGF₂α treatment group and control cows at the second GnRH treatment of the OV-Synch protocol (Barletta et al. 2018; Tippenhauer et al. 2021). It has been claimed that the luteolytic response to a single treatment of PGF₂α (regardless of the dose) is insufficient in young CLs (0 to 20% of cows had complete luteolysis); however, older CLs have a greater luteolytic response (Valldecabres-Torres et al. 2012). At the later stage of CL maturity, the luteolytic response depends on the PGF₂α dose (Valldecabres-Torres et al. 2012). Cows in different physiological statuses might be responsive to PGF₂α at an earlier stage of CL maturation (Nascimento et al. 2014). As evidence, on day 5 of the oestrus cycle, heifers were responsive to a single PGF₂α treatment, but none of the none-lactating or lactating cows were responsive. Furthermore, on day 7 of the cycle, the response rate of none-lactating cows was higher than those of heifers and lactating cows. Therefore, the differences observed in the response rate in various studies can be due to variations in physiological state or breed of cow used in these experiments (Momont and Seguin, 1984). It has been claimed that PGF₂α invokes some but not all of the biological responses in younger compared with older CL (Mondal et al. 2011). Receptors of PGF₂α can primarily be found on large luteal cells of CL (Anderson et al. 2001), either with or without luteolytic capacity (Diaz et al. 2002). In the present study, the the concentration of progesterone was 0.74 ± 0.23, 0.75 ± 0.26 and 0.76 ± 0.39 in the single PGF₂α dose and two doses of PGF₂α administered 12 and 24 h apart, respectively, on day 3. The concentration of progesterone was not significantly different among various groups. Consistent results have been reported from cows in the final stage of OV-Synch, under treatment with GnRH (Brusveen et al. 2009). Contradictory results are also available, in cows during the OV-Synch protocol. The circulating P₄ concentrations at 56 h after PGF₂α treatment were greater for cows receiving a single dose than two doses (Wiltbank et al. 2015). Furthermore, Giordano et al. (2013) reported an increased number of cows with low P₄ concentrations at final GnRH during an OV-Synch protocol. Another study showed that cows receiving two doses of PGF₂α treatments had lower P₄ at final GnRH compared to cows receiving a single dose of PGF₂α in OV-Synch protocol and pre-synchronisation with GnRH followed by an OV-Synch protocol after 6 days (Nascimento et al. 2014). Cows treated with a double dose of PGF₂α (50 mg) and two doses (given at 8-hour intervals) had lower P₄ concentrations 12 and 24 hours after the treatment (0–24 hours) (Nascimento et al. 2014). According to our results, all the animals were in oestrus at the same rate and there was no significant difference between single and multiple injections of PGF₂α. Consistently, a recent study showed the same proportion of cows in oestrus in the CO-Synch protocol used (Alnimer et al. 2019). Our study showed that the two PGF₂α treatments had no significant effect on P/AI in cows at the first service. But, treatment with a second dose of PGF₂α 12 and 24 h induced about 7% more pregnancies compared with the control group (40.0% and 41.2% respectively, vs. 33.3%) although, it was not significant. Also, the other observed a 5-7% for greater (not significant) P/AI for cows with a second dose of PGF₂α compared (35.4% and 36.5%) with control cows (30.7% and 29.0%) (Barletta et al. 2018; Kuru et al. 2020). In contrast, previous studies showed that heifers treated with two doses of PGF₂α at 6-hours intervals on day 5 had greater P/AI than those treated with two Co- PGF₂α or a single dose of PGF₂α in a 5-day CO-Synch ‏CIDR protocol (Say et al. 2016). Treatment with a second dose of PGF₂α during the OV-Synch protocol induced about 10% more pregnancies (Giordano et al. 2011; Tippenhauer et al. 2021). In consent with our study, one or two doses of PGF₂α at CIDR removal resulted in similar P/AI. The P/AI was 51.2%, 51.9%, for a single‏ and‏ two PGF₂α injections, respectively, in a 5-day progesterone-based CO-Synch protocol (Kasimanickam et al. 2014). Although two doses of PGF₂α have been shown to successfully induce luteolysis of early CL of fewer than 5 days old, the procedure did not always improve fertility compared with a single dose of PGF₂α (Kasimanickam et al. 2009; Peterson et al. 2011). No differences in P/AI were observed between a single and two doses of PGF₂α in dairy heifers (Rabaglino et al. 2010), but multiple injections increased the P/AI in dairy cows (Cruppe et al. 2010). Increasing the dose of PGF₂α from 500 mg to 750 mg had no significant effect on cows during Double-Ovsynch (Giordano et al. 2013). The double dose of PGF2α (50 mg) don’t affect P/AI compared with control cows (25 mg) in a 7-d Ovsynch protocol (30.7 vs. 32.4 P=0.30 and 31.8 vs. 33.4 P=0.46) (Barletta et al. 2018; Tippenhauer et al. 2021). However, the observed differences in response rate following a single or multiple injections or increasing the dose of PGF₂α in different studies can be related to differences in the luteinisation process and the age of CL (young vs. old). The younger CL does not regress after a single dose of PGF₂α treatment and needs an additional dose of PGF₂α during PGF₂α protocols (Nascimento et al. 2014).

 

CONCLUSION

In conclusion, single or two doses of PGF2α at 12 and 24-hour intervals during the middle stage of the estrous cycle on the equally effective for luteolysis process. In addition, estrus and pregnancy rates did not vary when single or two doses of PGF2α are used for the luteolysis in cows. Of course, using an additional dose of PGF₂α can be of a small benefit, but it is not significant.

 

ACKNOWLEDGEMENT

The authors thank the owners and staff of the Moghan Agro-industry Company for their cooperation.

مراجع

Ahuja C., Montiel F., Canseco R., Silva E. and Mapes G. (2005). Pregnancy rate following GnRH+ PGF2α treatment of low body condition, anestrous Bos taurus by Bos indicus crossbred cows during the summer months in a tropical environment. Anim. Reprod. Sci. 87, 203-213.

Alnimer M.A., Abedal-Majed M.A. and Shamoun A.I. (2019). Effect of two prostaglandin injections on days 5 and 6 in a timed AI protocol after estrus expression on pregnancy outcomes in dairy cows during cold or hot seasons of the year. Arch. Anim. Breed. 62, 161-168.

Anderson L.E., Wu Y.L., Tsai S.J. and Wiltbank M.C. (2001). Prostaglandin F2α receptor in the corpus luteum: Recent information on the gene, messenger ribonucleic acid, and protein. Biol. Reprod. 64, 1041-1047.

Atanasov B., Dovenski T., Celeska I. and Stevenson J. (2021). Luteolysis, progesterone, and pregnancy per insemination after modifying the standard 7-day Ovsynch program in Holstein-Friesian and Holstein cows. J. Dairy Sci. 104, 7272-7282.

Barletta R., Carvalho P., Santos V., Melo L., Consentini C., Netto A. and Fricke P. (2018). Effect of dose and timing of prostaglandin F2α treatments during a resynch protocol on luteal regression and fertility to timed artificial insemination in lactating Holstein cows. J. Dairy Sci. 101, 1730-1736.

Borchardt S., Pohl A., Carvalho P., Fricke P. and Heuwieser W. (2018). Effect of adding a second prostaglandin F2α injection during the ovsynch protocol on luteal regression and fertility in lactating dairy cows: A meta-analysis. J. Dairy Sci. 101, 8566-8571.

Brusveen D., Souza A. and Wiltbank M. (2009). Effects of additional prostaglandin F2α and estradiol-17β during Ovsynch in lactating dairy cows. J. Dairy Sci. 92, 1412-1422.

Cartmill J., El-Zarkouny S., Hensley B., Lamb G. and Stevenson J. (2001). Stage of cycle, incidence, and timing of ovulation, and pregnancy rates in dairy cattle after three timed breeding protocols. J. Dairy Sci. 84, 1051-1059.

Carvalho P., Fuenzalida M., Ricci A., Souza A., Barletta R., Wiltbank M. and Fricke P. (2015). Modifications to Ovsynch improve fertility during resynchronization: Evaluation of presynchronization with gonadotropin-releasing hormone 6 d before initiation of Ovsynch and addition of a second prostaglandin F2α treatment. J. Dairy Sci. 98, 8741-8752.

Cruppe L., Souto L., Maquivar M., Gunn P., Mussard M., Wolfenson D., Pires A., Bridges G. and Day M. (2010). Use of two coincident doses of PGF2 alpha with the 5-d CO-Synch plus CIDR estrous synchronization program. J. Anim. Sci. 88, 768-768.

Diaz F.J., Anderson L.E., Wu Y.L., Rabot A., Tsai S.J. and Wiltbank M.C. (2002). Regulation of progesterone and prostaglandin F2α production in the CL. Mol. Cell. Endocrinol. 191, 65-80.

El-Zarkouny S., Cartmill J., Hensley B. and Stevenson J. (2004). Pregnancy in dairy cows after synchronized ovulation regimens with or without presynchronization and progesterone. J. Dairy Sci. 87, 1024-1037.

Ginther O. (2007). Color-Doppler Ultrasonography. Equiservices Publishing, Wisconsin, USA.

Ginther O., Araujo R., Palhao M., Rodrigues B. and Beg M. (2009). Necessity of sequential pulses of prostaglandin F2alpha for complete physiologic luteolysis in cattle. Biol. Reprod. 80, 641-648.

Giordano J.O., Fricke P., Wiltbank M. and Cabrera V. (2011). An economic decision-making support system for selection of reproductive management programs on dairy farms. J. Dairy Sci. 94, 6216-6232.

Giordano J.O., Wiltbank M., Guenther J., Ares M., Lopes Jr G., Herlihy M. and Fricke P. (2012a). Effect of presynchronization with human chorionic gonadotropin or gonadotropin-releasing hormone 7 days before resynchronization of ovulation on fertility in lactating dairy cows. J. Dairy Sci. 95, 5612-5625.

Giordano J.O., Wiltbank M., Guenther J., Pawlisch R., Bas S., Cunha A. and Fricke P. (2012b). Increased fertility in lactating dairy cows resynchronized with Double-Ovsynch compared with Ovsynch initiated 32 d after timed artificial insemination. J. Dairy Sci. 95, 639-653.

Giordano J.O., Wiltbank M.C., Fricke P.M., Bas S., Pawlisch R., Guenther J.N. and Nascimento A.B. (2013). Effect of increasing GnRH and PGF2α dose during Double-Ovsynch on ovulatory response, luteal regression, and fertility of lactating dairy cows. Theriogenology. 80, 773-783.

Gümen A., Guenther J. and Wiltbank M. (2003). Follicular size and response to Ovsynch versus detection of estrus in anovular and ovular lactating dairy cows. J. Dairy Sci. 86, 3184-3194.

Kasimanickam R., Day M., Rudolph J., Hall J. and Whittier W. (2009). Two doses of prostaglandin improve pregnancy rates to timed-AI in a 5-day progesterone-based synchronization protocol in beef cows. Theriogenology. 71, 762-767.

Kasimanickam R., Firth P., Schuenemann G.M., Whitlock B., Gay J., Moore D., Hall J. and Whittier W. (2014). Effect of the first GnRH and two doses of PGF2α in a 5-day progesterone-based CO-Synch protocol on heifer pregnancy. Theriogenology. 81, 797-804.

Kayacik V., Salmanoğlu M.R., Polat B. And Özlüer A. (2006). Evaluation of the corpus luteum size throughout the cycle by ultrasonography and progesterone assay in cows. Turkish J. Vet. Anim. Sci. 29, 1311-1316.

Kuru M., Kacar C., Oral H., Kaya S., Cetin N., Kaya D. and Demir M.C. (2020). Effect of two prostaglandin F2α injections administered 24 hours apart on the pregnancy rate of Simmental cows subjected to the Ovsynch or Ovsynch+ Controlled internal drug release (CIDR) protocols. Med. Weter. 76, 660-665.

Levy N., Kobayashi S.I., Roth Z., Wolfenson D., Miyamoto A. and Meidan R. (2000). Administration of prostaglandin F2α during the early bovine luteal phase does not alter the expression of ET-1 and of its type A receptor: A possible cause for corpus luteum refractoriness. Biol. Reprod. 63, 377-382.

Lopez H., Satter L. and Wiltbank M. (2004). Relationship between level of milk production and estrous behavior of lactating dairy cows. Anim. Reprod. Sci. 81, 209-223.

Momont H. and Seguin B. (1984). Influence of day of estrous cycle on response to PGF2 alpha products: implications for AI programs for dairy cattle. Pp. 10-14 in Int. Congr. Anim. Reprod. Art. Insem., University of Illinois at Urbana-Champaign, Illinois, USA.

Mondal M., Schilling B., Folger J., Steibel J.P., Buchnick H., Zalman Y., Ireland J.J., Meidan R. and Smith G.W. (2011). Deciphering the luteal transcriptome: Potential mechanisms mediating stage-specific luteolytic response of the corpus luteum to prostaglandin F2α. Physiol. Genomics. 43, 447-456.

Moreira F., De la Sota R., Diaz T. and Thatcher W. (2000). Effect of day of the estrous cycle at the initiation of a timed artificial insemination protocol on reproductive responses in dairy heifers. J. Dairy Sci. 78, 1568-1576.

Nascimento A.B., Souza A.H., Keskin A., Sartori R. and Wiltbank M.C. (2014). Lack of complete regression of the day 5 corpus luteum after one or two doses of PGF2α in nonlactating Holstein cows. Theriogenology. 81, 389-395.

Peralta O., Pearson R. and Nebel R. (2005). Comparison of three estrus detection systems during summer in a large commercial dairy herd. Anim. Reprod. Sci. 87, 59-72.

Peterson C., Alkar A., Smith S., Kerr S., Hall J., Moore D. and Kasimanickam R. (2011). Effects of one versus two doses of prostaglandin F2 alpha on AI pregnancy rates in a 5-day, progesterone-based, CO-Synch protocol in crossbred beef heifers. Theriogenology. 75, 1536-1542.

Pierson R. and Ginther O. (1984). Ultrasonography of the bovine ovary. Theriogenology. 21, 495-504.

Pieterse M., Taverne M., Kruip T. and Willemse A. (1990). Detection of corpora lutea and follicles in cows: A comparison of transvaginal ultrasonography and rectal palpation. Vet. Record. 126, 552-554.

Pursley J., Wiltbank M., Stevenson J., Ottobre J., Garverick H. and Anderson L. (1997). Pregnancy rates per artificial insemination for cows and heifers inseminated at a synchronized ovulation or synchronized estrus. J. Dairy Sci. 80, 295-300.

Rabaglino M., Risco C., Thatcher M.J., Kim I., Santos J. and Thatcher W. (2010). Application of one injection of prostaglandin F2α in the five-day Co-Synch+ CIDR protocol for estrous synchronization and resynchronization of dairy heifers. J. Dairy Sci. 93, 1050-1058.

Ribeiro E., Bisinotto R., Favoreto M., Martins L., Cerri R., Silvestre F., Greco L., Thatcher W. and Santos J. (2012). Fertility in dairy cows following presynchronization and administering twice the luteolytic dose of prostaglandin F2α as one or two injections in the 5-day timed artificial insemination protocol. Theriogenology. 78, 273-284.

Romano J.E., Thompson J.A., Forrest D.W., Westhusin M.E., Tomaszweski M.A. and Kraemer D.C. (2006). Early pregnancy diagnosis by transrectal ultrasonography in dairy cattle. Theriogenology. 66, 1034-1041.

Santos J., Narciso C., Rivera F., Thatcher W. and Chebel R. (2010). Effect of reducing the period of follicle dominance in a timed artificial insemination protocol on reproduction of dairy cows. J. Dairy Sci. 93, 2976-2988.

Say E., Çoban S., Nak Y., Nak D., Kara U., White S., Kasimanickam V. and Kasimanickam R. (2016). Fertility of Holstein heifers after two doses of PGF2α in 5-day CO-Synch progesterone-based synchronization protocol. Theriogenology. 86, 988-993.

Schams D. and Berisha B. (2004). Regulation of corpus luteum function in cattle–an overview. Reprod. Domest. Anim. 39, 241-251.

Senger P. (1994). The estrus detection problem: New concepts, technologies, and possibilities. J. Dairy Sci. 77, 2745-2753.

Souza A., Gümen A., Silva E., Cunha A., Guenther J., Peto C., Caraviello D. and Wiltbank M. (2007). Supplementation with estradiol-17β before the last gonadotropin-releasing hormone injection of the Ovsynch protocol in lactating dairy cows. J. Dairy Sci. 90, 4623-4634.

SPSS Inc. (2011). Statistical Package for Social Sciences Study. SPSS for Windows, Version 20. Chicago SPSS Inc., USA.

Tippenhauer C., Steinmetz I., Heuwieser W., Fricke P., Lauber M., Cabrera E. and Borchardt S. (2021). Effect of dose and timing of prostaglandin F2α treatments during a 7-d Ovsynch protocol on progesterone concentration at the end of the protocol and pregnancy outcomes in lactating Holstein cows. Theriogenology. 162, 49-58.

Valldecabres-Torres X., García-Roselló E., García-Muñoz A. and Cuervo-Arango J. (2012). Effects of d-cloprostenol dose and corpus luteum age on ovulation, luteal function, and morphology in nonlactating dairy cows with early corpora lutea. J. Dairy Sci. 95, 4389-4395.

Washburn S., Silvia W., Brown C., McDaniel B. and McAllister A. (2002). Trends in reproductive performance in southeastern Holstein and Jersey DHI herds. J. Dairy Sci. 85, 244-251.

Wenzinger B. and Bleul U. (2012). Effect of a prostaglandin F2α analogue on the cyclic corpus luteum during its refractory period in cows. BMC Vet. Res. 8, 220-228.

Wiltbank M., Lopez H., Sartori R., Sangsritavong S. and Gümen A. (2006). Changes in reproductive physiology of lactating dairy cows due to elevated steroid metabolism. Theriogenology. 65, 17-29.

Wiltbank M.C. and Pursley J.R. (2014). The cow as an induced ovulator: Timed AI after synchronization of ovulation. Theriogenology. 81, 170-185.

Wiltbank M.C., Baez G.M., Cochrane F., Barletta R.V., Trayford C.R. and Joseph R.T. (2015). Effect of a second treatment with prostaglandin F2α during the Ovsynch protocol on luteolysis and pregnancy in dairy cows. J. Dairy Sci. 98, 8644-8654.