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Journal of Animal Reproduction and Biotechnology 2023; 38(4): 263-267

Published online December 31, 2023

https://doi.org/10.12750/JARB.38.4.263

Copyright © The Korean Society of Animal Reproduction and Biotechnology.

A study on the correlation between vaginal conductivity and estrus in Hanwoo (Bos taurus coreanae) cows

Junkoo Yi1,# , Jinyeon Park2,4,# , Jaejung Ha2 , Daejung Yu3 , Woo-Sung Kwon4,* and Daehyun Kim5,*

1School of Animal Life Convergence Science, Hankyong National University, Ansung 17579, Korea
2Gyeongsangbuk-Do Livestock Research Institute, Yeongju 36052, Korea
3Chonnam Agricultural Research & Extension Services Livestock Institute, Gangjin 59213, Korea
4Department of Animal Science and Biotechnology, Kyungpook National University, Sangju 37224, Korea
5Department of Animal Science, Chonnam National University, Gwangju 61186, Korea

Correspondence to: Daehyun Kim
E-mail: kimdhbio@jnu.ac.kr

Woo-Sung Kwon
E-mail: wskwon@knu.ac.kr

#These authors contributed equally to this work.

Received: October 16, 2023; Revised: October 25, 2023; Accepted: October 25, 2023

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Background: Estrus in cows can be detected through vaginal electrical resistance or conductivity. However, there are no studies measuring vaginal electrical resistance in Hanwoo cows. This study aims to measure the vaginal electrical resistance value in Hanwoo cows and compare it with estrus and ovulation.
Methods: Vaginal electrical resistance values of 73 Hanwoo cows were measured before and after estrus at the Gyeongsangbuk-do Livestock Research Institute. Measurements were taken on days -6, -3, -2, -1, 0, 1, 2, 3, and 6 of artificial insemination. Large follicles and ovulation were confirmed using transvaginal ultrasonography.
Results: The vaginal electrical resistance averaged 225.6 ± 6.3 Ω days before the artificial insemination date, decreasing until the day of artificial insemination. The average vaginal electrical resistance was 163.7 ± 4.6 Ω on the date of artificial insemination, and 188.8 ± 4.3 Ω one day after artificial insemination, when large follicles were observed. In addition, on the 6th day after artificial insemination, the vaginal electrical resistance averaged 231.4 ± 5.5, which was similar to the 6th day before artificial insemination (222.5 ± 6.3). Transvaginal ultrasonography showed that most of the cows ovulated one day after artificial insemination.
Conclusions: The accuracy of estrus is high if the vaginal electrical resistance is measured for cows with confirmed estrus, making is a potentially useful for determining the timing of artificial insemination.

Keywords: estrus, Hanwoo, ovulation, vaginal conductivity, vaginal electrical resistance

It is important to check the estrus of the cows to increase the possibility of a successful pregnancy, However, the accuracy of visual estrus detection for large-scale breeding is relatively low (Williamson et al., 1972, Senger, 1994, Aoki et al., 2005, Lima et al., 2010, Lamb and Mercadante, 2016). In order to improve the accuracy of estrus detection, recent studies have reported that the estrus of cows can be predicted using necklace-type sensors and ruminoreticular biosensors (Williamson et al., 1972, Senger, 1994, Aoki et al., 2005, Kim et al., 2017a, Kim et al., 2017b, Choi et al., 2020, Kim et al., 2021a, Kim et al., 2021b, Kim et al., 2021c, Kim et al., 2023), which detect increased activity during estrus and short-term activity increases before parturition (Titler et al., 2015). Notably, the accuracy of ruminoreticular biosensors for estrus confirmation was higher than that of visual observation, providing more opportunities for artificial insemination and improved reproduction rate (Kim et al., 2023). During the estrus, cows demonstrate characteristics such as mounting, increased body temperature and activity, and copious vaginal mucus discharge which is commonly observed around the vulva and in the tail (Talukder et al., 2018, Higaki et al., 2019). Recent studies measuring vaginal electrical resistance values in ewes, sows, female dogs, red foxes, and rats, and analyzed its correlation with estrus in Japanese Black heifers and cows have been reported (Talukder et al., 2018, Yatu et al., 2018, Higaki et al., 2019, Chesney et al., 2020, Lindh et al., 2020, Glencorse et al., 2023). However, there are no studies measuring vaginal electrical resistance in Hanwoo cows. This study thus aims to measure the vaginal electrical resistance in Hanwoo cows before and after artificial insemination, and analyze its relationship with estrus and ovulation.

Animal management

Hanwoo cows (n = 73) raised according to the Hanwoo Korean Feeding Standard at the Gyeongsangbuk-do Livestock Research Institute with sufficient space and stanchions were included in the study. The study was approved by the Institutional Animal Care and Use Committee (IACUC) of the Gyeongsangbuk-do Livestock Research Institute.

Estrus synchronization

The cows were synchronized using a Gonadotropin-releasing hormone-based fixed-time artificial insemination method. Detailed hormone treatment methods are detailed in Fig. 1, and additional explanations are provided in the paper published by Kim et al (Kim et al., 2023).

Figure 1. Summary of experimental methods. Estrus synchronized by the GnRH based FTAI methods. vaginal electrical resistance was measured on days -6, -3, -2, -1, 0, 1, 2, 3, and 6 of artificial insemination. Follicle size was measured on days -2, -1, 0, 1, and 2.

Vaginal electrical resistance

Vaginal electrical resistance (ohm, Ω) was measured using an electronic estrous detector (DRAMINSKI ED2, Poland) on days -6, -3, -2, -1, 0, 1, 2, 3, and 6 of artificial insemination. To increase the accuracy, all the measurements were taken by the same evaluator at the same time.

Before using A, the device was washed in sterile distilled water, and then inserted into the vagina and rotated. The measurements were taken three times, and an average of the three values was recorded. A detailed measurement method was described previously (https://www.youtube.com/watch?v=eSZqcPSetO8, https://www.youtube.com/watch?v=tcIXI_5rVB4) (Talukder et al., 2018).

Ovulation test

Ovulation was evaluated using transvaginal ultrasonography. The diameters of the follicles (mm) are provided in Supplementary Fig. 1. If ovulation was not detected with ultrasound, the cow was excluded from the results (Supplementary Fig. 2).

Statistical analysis

One-way Analysis of variance (ANOVA) analysis was used to statistically analyze the magnitude of vaginal electrical resistance and follicle size in accordance with the estrus cycle through GraphPad Prism (version 8.0.1; GraphPad Software Inc., USA).

A total of 73 cows were included in the study. The average vaginal electrical resistance was 225.6 ± 6.3 Ω 6 days before the artificial insemination, and continued to decrease until artificial insemination (Fig. 2 and Table 1). The average vaginal electrical resistance was 163.7 ± 4.6 Ω based on the artificial insemination date, and the average vaginal electrical resistance was 188.8 ± 4.3 Ω one day after the artificial insemination date, which corresponds with ovulation (Fig. 2 and Table 1). In addition, the vaginal electrical resistance increased on the 6th day after artificial insemination, with an average of 231.4 ± 5.5 Ω, which was similar to the 6th day before artificial insemination (Fig. 2 and Table 1). Notably, the vaginal electrical resistance measured on days -6, -3, -2, -1, 0, 1, 2, 3, 6 modification with one-way ANOVA was significantly different (p < 0.001). The follicular diameter was the largest at 12.8 ± 0.27 mm on day 0 and 4.7 ± 0.27 mm on day 1 of artificial insemination. It can be confirmed that the large follicles have ovulated 1 day after artificial insemination (Fig. 3).

Table 1 . Vaginal electrical resistance during the estrus cycle

Day of artificial inseminationNo. of cowsElectric resistance (Ω) (Mean ± SEM)
-650225.6 ± 6.3
-350194.6 ± 5.8
-250186.4 ± 5.0
-149179.6 ± 5.8
092163.7 ± 4.6
183188.8 ± 4.3
250195.4 ± 4.6
350212.0 ± 4.9
649231.4 ± 5.5

Figure 2. Changes in vaginal electrical resistance in Hanwoo cows during the estrus cycle (n = 73). The black line connected by blank round dots (Ο) represents average of vaginal electrical resistance. Day 0 represents the time of artificial insemination. All results are presented as mean ± SEM. The statistical significance level was p < 0.001.
Figure 3. Changes in follicle size of in Hanwoo cows during the estrus cycle (n = 73). The gray bars represent the average follicle size (mm). Day 0 represents the time of artificial insemination. All results are presented as mean ± SEM. The statistical significance level was p < 0.001.

During estrus, vaginal electrical resistance value can be significantly lowered due to the large amount of mucus is present in the vagina. According to a study on of indigenous ewes, vaginal electrical resistance ranged from 370.0 ± 82.0 – 416.7 ± 51.3 Ω on the day of estrus, and increased significantly to 600 Ω during non-estrus periods (Talukder et al., 2018). The vaginal conductivity ratio of Japanese Black heifers and cows was very high on the estrus day compared to the non-estrus days (Higaki et al., 2019). It is difficult to accurately compare the vaginal conductivity ratio reported by Higaki et al. as it shows contradicting results on vaginal electrical conductivity (Higaki et al., 2019). However, vaginal electrical resistance is inversely proportional to vaginal conductivity ratio, so it can be seen that it eventually shows the same pattern. Similarly, the follicular diameter is the largest on the day of estrus. The follicle size decreases because ovulation occurs one day after estrus. In addition, in Japanese Black heifers and cows, the vaginal temperature and the vaginal conductivity ratio throughout the duration of the estrus cycle were compared, and both increased on the day of estrus. We also previously reported that the ruminoraticular temperature increased for about 24 hours in the estrus cycle (Kim et al., 2023). Similarly, the present study shows that the ruminoraticular temperature increases and the vacuum electrical resistance decreases on the day of estrus.

It can be useful to determine the timing of artificial insemination if the vaginal electrical resistance is measured for cows with confirmed estrus signs such as mounting, increased body temperature and activity, and mucus secretion. This can be used as raw data for the future development of biosensors that simultaneously measure vaginal electrical resistance, vaginal temperature, and vaginal activity, which can be used as a tool to determine the optimal timing of artificial insemination.

Conceptualization, J.Y., J.P., J.H., D.Y., W-S.K., and D.K.; methodology, J.Y., J.P., J.H., D.Y., W-S.K., D.K.; investigation, J.Y., J.P., J.H., D.Y.; data curation, J.Y., J.P., J.H., D.Y.; writing—original draft preparation, J.Y., J.P.; writing—review and editing, W-S.K., D.K.; supervision, W-S.K., D.K.; project administration, W-S.K., D.K.; funding acquisition, W-S.K., D.K.

This study was conducted in accordance with the Declaration of Helsinki and was approved by the Institutional Animal Care and Use Committee (IACUC) of the Gyeongsangbuk-do Livestock Research Institute, Yeongju, Korea (protocol code GAEC/140 approved on December 14, 2021).

  1. Aoki M, Suzuki O. 2005. Predicting time of parturition from changing vaginal temperature measured by data-logging apparatus in beef cows with twin fetuses. Anim. Reprod. Sci. 86:1-12.
    Pubmed CrossRef
  2. Chesney KL, Bryda EC. 2020. Using vaginal impedance measurement to identify proestrus in rats given luteinizing hormone releasing hormone (LHRH) agonist. J. Am. Assoc. Lab. Anim. Sci. 59:282-287.
    Pubmed KoreaMed CrossRef
  3. Choi W, Ro Y, Hong L, Ahn S, Kim H, Choi C, Kim D. 2020. Evaluation of ruminal motility using an indwelling 3-axis accelerometer in the reticulum in cattle. J. Vet. Med. Sci. 82:1750-1756.
    Pubmed KoreaMed CrossRef
  4. Glencorse D, Bathgate R. 2023. Vaginal and vestibular electrical resistance as an alternative marker for optimum timing of artificial insemination with liquid-stored and frozen-thawed spermatozoa in sows. Sci. Rep. 13:12103.
    Pubmed KoreaMed CrossRef
  5. Higaki S, Miura R, Suda T, Andersson LM, Okada H, Zhang Y, Itoh T, Yoshioka K. 2019. Estrous detection by continuous measurements of vaginal temperature and conductivity with supervised machine learning in cattle. Theriogenology 123:90-99.
    Pubmed CrossRef
  6. Kim D, Ha J, Moon J, Kim D, Lee W, Lee C, Yi J. 2021a. Increased ruminoreticular temperature and body activity after foot-and-mouth vaccination in pregnant Hanwoo (Bos taurus coreanae) cows. Vaccines (Basel) 9:1227.
    Pubmed KoreaMed CrossRef
  7. Kim D, Kwon WS, Ha J, Yi J. 2023. Increased accuracy of estrus prediction using ruminoreticular biocapsule sensors in Hanwoo (Bos taurus coreanae) cows. J. Anim. Sci. Technol. 65:759-766.
    Pubmed KoreaMed CrossRef
  8. Kim D, Moon J, Ha J, Yi J. 2021b. Effect of foot-and-mouth disease vaccination on acute phase immune response and anovulation in Hanwoo (Bos taurus coreanae). Vaccines (Basel) 9:419.
    Pubmed KoreaMed CrossRef
  9. Kim DH, Ha JJ, Yi JK, Kim BK, Kwon WS, Ye BH, Lee Y. 2021c. Differences in ruminal temperature between pregnant and non-pregnant Korean cattle. J. Anim. Reprod. Biotechnol. 36:45-50.
    CrossRef
  10. Kim H, Oh S, Choi B. 2017a. Real-time monitoring method of cattle's temperature for FMD prevention and its case studies. J. Korean Inst. Inf. Technol. 15:141-150.
    CrossRef
  11. Kim H, Oh S, Choi B. 2017b. Real-time temperature monitoring to enhance estrus detection in cattle utilizing ingestible bio-sensors: method & case studies. J. Korean Inst. Inf. Technol. 15:65-75.
    CrossRef
  12. Lamb GC and Mercadante VR. 2016. Synchronization and artificial insemination strategies in beef cattle. Vet. Clin. North Am. Food Anim. Pract. 32:335-347.
    Pubmed CrossRef
  13. Lima FS, De Vries A, Risco CA, Thatcher WW. 2010. Economic comparison of natural service and timed artificial insemination breeding programs in dairy cattle. J. Dairy Sci. 93:4404-4413.
    Pubmed CrossRef
  14. Lindh L, Lindeberg H, Banting A, Banting S, Sainmaa S, Beasley S, Peltoniemi OAT. 2020. Administration of aromatase inhibitor MPV-2213ad to blue fox vixens (Vulpes lagopus) as a model for contraception in female dogs. Theriogenology 152:53-63.
    Pubmed CrossRef
  15. Senger PL. 1994. The estrus detection problem: new concepts, technologies, and possibilities. J. Dairy Sci. 77:2745-2753.
    Pubmed CrossRef
  16. Talukder MRI, Hasan M, Rosy TA, Juyena NS. 2018. Monitoring vaginal electrical resistance, follicular waves, and hormonal profile during oestrous cycle in the transition period in Bangladeshi sheep. J. Vet. Res. 62:571-579.
    Pubmed KoreaMed CrossRef
  17. Titler M, Maquivar MG, Bas S, Rajala-Schultz PJ, Gordon E, McCullough K, Schuenemann GM. 2015. Prediction of parturition in Holstein dairy cattle using electronic data loggers. J. Dairy Sci. 98:5304-5312.
    Pubmed CrossRef
  18. Williamson NB, Morris RS, Cannon CM. 1972. A study of oestrous behaviour and oestrus detection methods in a large commercial dairy herd. I. The relative efficiency of methods of oestrus detection. Vet. Rec. 91:50-58.
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  19. Yatu M, Sato M, Kobayashi J, Ichijo T, Satoh H, Sato S. 2018. Collection and frozen storage of semen for artificial insemination in red foxes (Vulpes vulpes). J. Vet. Med. Sci. 80:1762-1765.
    Pubmed KoreaMed CrossRef

Article

Original Article

Journal of Animal Reproduction and Biotechnology 2023; 38(4): 263-267

Published online December 31, 2023 https://doi.org/10.12750/JARB.38.4.263

Copyright © The Korean Society of Animal Reproduction and Biotechnology.

A study on the correlation between vaginal conductivity and estrus in Hanwoo (Bos taurus coreanae) cows

Junkoo Yi1,# , Jinyeon Park2,4,# , Jaejung Ha2 , Daejung Yu3 , Woo-Sung Kwon4,* and Daehyun Kim5,*

1School of Animal Life Convergence Science, Hankyong National University, Ansung 17579, Korea
2Gyeongsangbuk-Do Livestock Research Institute, Yeongju 36052, Korea
3Chonnam Agricultural Research & Extension Services Livestock Institute, Gangjin 59213, Korea
4Department of Animal Science and Biotechnology, Kyungpook National University, Sangju 37224, Korea
5Department of Animal Science, Chonnam National University, Gwangju 61186, Korea

Correspondence to:Daehyun Kim
E-mail: kimdhbio@jnu.ac.kr

Woo-Sung Kwon
E-mail: wskwon@knu.ac.kr

#These authors contributed equally to this work.

Received: October 16, 2023; Revised: October 25, 2023; Accepted: October 25, 2023

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background: Estrus in cows can be detected through vaginal electrical resistance or conductivity. However, there are no studies measuring vaginal electrical resistance in Hanwoo cows. This study aims to measure the vaginal electrical resistance value in Hanwoo cows and compare it with estrus and ovulation.
Methods: Vaginal electrical resistance values of 73 Hanwoo cows were measured before and after estrus at the Gyeongsangbuk-do Livestock Research Institute. Measurements were taken on days -6, -3, -2, -1, 0, 1, 2, 3, and 6 of artificial insemination. Large follicles and ovulation were confirmed using transvaginal ultrasonography.
Results: The vaginal electrical resistance averaged 225.6 ± 6.3 Ω days before the artificial insemination date, decreasing until the day of artificial insemination. The average vaginal electrical resistance was 163.7 ± 4.6 Ω on the date of artificial insemination, and 188.8 ± 4.3 Ω one day after artificial insemination, when large follicles were observed. In addition, on the 6th day after artificial insemination, the vaginal electrical resistance averaged 231.4 ± 5.5, which was similar to the 6th day before artificial insemination (222.5 ± 6.3). Transvaginal ultrasonography showed that most of the cows ovulated one day after artificial insemination.
Conclusions: The accuracy of estrus is high if the vaginal electrical resistance is measured for cows with confirmed estrus, making is a potentially useful for determining the timing of artificial insemination.

Keywords: estrus, Hanwoo, ovulation, vaginal conductivity, vaginal electrical resistance

INTRODUCTION

It is important to check the estrus of the cows to increase the possibility of a successful pregnancy, However, the accuracy of visual estrus detection for large-scale breeding is relatively low (Williamson et al., 1972, Senger, 1994, Aoki et al., 2005, Lima et al., 2010, Lamb and Mercadante, 2016). In order to improve the accuracy of estrus detection, recent studies have reported that the estrus of cows can be predicted using necklace-type sensors and ruminoreticular biosensors (Williamson et al., 1972, Senger, 1994, Aoki et al., 2005, Kim et al., 2017a, Kim et al., 2017b, Choi et al., 2020, Kim et al., 2021a, Kim et al., 2021b, Kim et al., 2021c, Kim et al., 2023), which detect increased activity during estrus and short-term activity increases before parturition (Titler et al., 2015). Notably, the accuracy of ruminoreticular biosensors for estrus confirmation was higher than that of visual observation, providing more opportunities for artificial insemination and improved reproduction rate (Kim et al., 2023). During the estrus, cows demonstrate characteristics such as mounting, increased body temperature and activity, and copious vaginal mucus discharge which is commonly observed around the vulva and in the tail (Talukder et al., 2018, Higaki et al., 2019). Recent studies measuring vaginal electrical resistance values in ewes, sows, female dogs, red foxes, and rats, and analyzed its correlation with estrus in Japanese Black heifers and cows have been reported (Talukder et al., 2018, Yatu et al., 2018, Higaki et al., 2019, Chesney et al., 2020, Lindh et al., 2020, Glencorse et al., 2023). However, there are no studies measuring vaginal electrical resistance in Hanwoo cows. This study thus aims to measure the vaginal electrical resistance in Hanwoo cows before and after artificial insemination, and analyze its relationship with estrus and ovulation.

MATERIALS AND METHODS

Animal management

Hanwoo cows (n = 73) raised according to the Hanwoo Korean Feeding Standard at the Gyeongsangbuk-do Livestock Research Institute with sufficient space and stanchions were included in the study. The study was approved by the Institutional Animal Care and Use Committee (IACUC) of the Gyeongsangbuk-do Livestock Research Institute.

Estrus synchronization

The cows were synchronized using a Gonadotropin-releasing hormone-based fixed-time artificial insemination method. Detailed hormone treatment methods are detailed in Fig. 1, and additional explanations are provided in the paper published by Kim et al (Kim et al., 2023).

Figure 1.Summary of experimental methods. Estrus synchronized by the GnRH based FTAI methods. vaginal electrical resistance was measured on days -6, -3, -2, -1, 0, 1, 2, 3, and 6 of artificial insemination. Follicle size was measured on days -2, -1, 0, 1, and 2.

Vaginal electrical resistance

Vaginal electrical resistance (ohm, Ω) was measured using an electronic estrous detector (DRAMINSKI ED2, Poland) on days -6, -3, -2, -1, 0, 1, 2, 3, and 6 of artificial insemination. To increase the accuracy, all the measurements were taken by the same evaluator at the same time.

Before using A, the device was washed in sterile distilled water, and then inserted into the vagina and rotated. The measurements were taken three times, and an average of the three values was recorded. A detailed measurement method was described previously (https://www.youtube.com/watch?v=eSZqcPSetO8, https://www.youtube.com/watch?v=tcIXI_5rVB4) (Talukder et al., 2018).

Ovulation test

Ovulation was evaluated using transvaginal ultrasonography. The diameters of the follicles (mm) are provided in Supplementary Fig. 1. If ovulation was not detected with ultrasound, the cow was excluded from the results (Supplementary Fig. 2).

Statistical analysis

One-way Analysis of variance (ANOVA) analysis was used to statistically analyze the magnitude of vaginal electrical resistance and follicle size in accordance with the estrus cycle through GraphPad Prism (version 8.0.1; GraphPad Software Inc., USA).

RESULTS

A total of 73 cows were included in the study. The average vaginal electrical resistance was 225.6 ± 6.3 Ω 6 days before the artificial insemination, and continued to decrease until artificial insemination (Fig. 2 and Table 1). The average vaginal electrical resistance was 163.7 ± 4.6 Ω based on the artificial insemination date, and the average vaginal electrical resistance was 188.8 ± 4.3 Ω one day after the artificial insemination date, which corresponds with ovulation (Fig. 2 and Table 1). In addition, the vaginal electrical resistance increased on the 6th day after artificial insemination, with an average of 231.4 ± 5.5 Ω, which was similar to the 6th day before artificial insemination (Fig. 2 and Table 1). Notably, the vaginal electrical resistance measured on days -6, -3, -2, -1, 0, 1, 2, 3, 6 modification with one-way ANOVA was significantly different (p < 0.001). The follicular diameter was the largest at 12.8 ± 0.27 mm on day 0 and 4.7 ± 0.27 mm on day 1 of artificial insemination. It can be confirmed that the large follicles have ovulated 1 day after artificial insemination (Fig. 3).

Table 1. Vaginal electrical resistance during the estrus cycle.

Day of artificial inseminationNo. of cowsElectric resistance (Ω) (Mean ± SEM)
-650225.6 ± 6.3
-350194.6 ± 5.8
-250186.4 ± 5.0
-149179.6 ± 5.8
092163.7 ± 4.6
183188.8 ± 4.3
250195.4 ± 4.6
350212.0 ± 4.9
649231.4 ± 5.5

Figure 2.Changes in vaginal electrical resistance in Hanwoo cows during the estrus cycle (n = 73). The black line connected by blank round dots (Ο) represents average of vaginal electrical resistance. Day 0 represents the time of artificial insemination. All results are presented as mean ± SEM. The statistical significance level was p < 0.001.
Figure 3.Changes in follicle size of in Hanwoo cows during the estrus cycle (n = 73). The gray bars represent the average follicle size (mm). Day 0 represents the time of artificial insemination. All results are presented as mean ± SEM. The statistical significance level was p < 0.001.

DISCUSSION

During estrus, vaginal electrical resistance value can be significantly lowered due to the large amount of mucus is present in the vagina. According to a study on of indigenous ewes, vaginal electrical resistance ranged from 370.0 ± 82.0 – 416.7 ± 51.3 Ω on the day of estrus, and increased significantly to 600 Ω during non-estrus periods (Talukder et al., 2018). The vaginal conductivity ratio of Japanese Black heifers and cows was very high on the estrus day compared to the non-estrus days (Higaki et al., 2019). It is difficult to accurately compare the vaginal conductivity ratio reported by Higaki et al. as it shows contradicting results on vaginal electrical conductivity (Higaki et al., 2019). However, vaginal electrical resistance is inversely proportional to vaginal conductivity ratio, so it can be seen that it eventually shows the same pattern. Similarly, the follicular diameter is the largest on the day of estrus. The follicle size decreases because ovulation occurs one day after estrus. In addition, in Japanese Black heifers and cows, the vaginal temperature and the vaginal conductivity ratio throughout the duration of the estrus cycle were compared, and both increased on the day of estrus. We also previously reported that the ruminoraticular temperature increased for about 24 hours in the estrus cycle (Kim et al., 2023). Similarly, the present study shows that the ruminoraticular temperature increases and the vacuum electrical resistance decreases on the day of estrus.

CONCLUSION

It can be useful to determine the timing of artificial insemination if the vaginal electrical resistance is measured for cows with confirmed estrus signs such as mounting, increased body temperature and activity, and mucus secretion. This can be used as raw data for the future development of biosensors that simultaneously measure vaginal electrical resistance, vaginal temperature, and vaginal activity, which can be used as a tool to determine the optimal timing of artificial insemination.

SUPPLEMENTARY MATERIALS

Acknowledgements

None.

Author Contributions

Conceptualization, J.Y., J.P., J.H., D.Y., W-S.K., and D.K.; methodology, J.Y., J.P., J.H., D.Y., W-S.K., D.K.; investigation, J.Y., J.P., J.H., D.Y.; data curation, J.Y., J.P., J.H., D.Y.; writing—original draft preparation, J.Y., J.P.; writing—review and editing, W-S.K., D.K.; supervision, W-S.K., D.K.; project administration, W-S.K., D.K.; funding acquisition, W-S.K., D.K.

Funding

None.

Ethical Approval

This study was conducted in accordance with the Declaration of Helsinki and was approved by the Institutional Animal Care and Use Committee (IACUC) of the Gyeongsangbuk-do Livestock Research Institute, Yeongju, Korea (protocol code GAEC/140 approved on December 14, 2021).

Consent to Participate

Not applicable.

Consent to Publish

All authors agreed to the terms outlined in this document and approved it’s submission of this manuscript for publication.

Availability of Data and Materials

The data analyzed or generated during this study are available upon request from the corresponding author.

Conflicts of Interest

No potential conflict of interest relevant to this article was reported.

Fig 1.

Figure 1.Summary of experimental methods. Estrus synchronized by the GnRH based FTAI methods. vaginal electrical resistance was measured on days -6, -3, -2, -1, 0, 1, 2, 3, and 6 of artificial insemination. Follicle size was measured on days -2, -1, 0, 1, and 2.
Journal of Animal Reproduction and Biotechnology 2023; 38: 263-267https://doi.org/10.12750/JARB.38.4.263

Fig 2.

Figure 2.Changes in vaginal electrical resistance in Hanwoo cows during the estrus cycle (n = 73). The black line connected by blank round dots (Ο) represents average of vaginal electrical resistance. Day 0 represents the time of artificial insemination. All results are presented as mean ± SEM. The statistical significance level was p < 0.001.
Journal of Animal Reproduction and Biotechnology 2023; 38: 263-267https://doi.org/10.12750/JARB.38.4.263

Fig 3.

Figure 3.Changes in follicle size of in Hanwoo cows during the estrus cycle (n = 73). The gray bars represent the average follicle size (mm). Day 0 represents the time of artificial insemination. All results are presented as mean ± SEM. The statistical significance level was p < 0.001.
Journal of Animal Reproduction and Biotechnology 2023; 38: 263-267https://doi.org/10.12750/JARB.38.4.263

Table 1 . Vaginal electrical resistance during the estrus cycle.

Day of artificial inseminationNo. of cowsElectric resistance (Ω) (Mean ± SEM)
-650225.6 ± 6.3
-350194.6 ± 5.8
-250186.4 ± 5.0
-149179.6 ± 5.8
092163.7 ± 4.6
183188.8 ± 4.3
250195.4 ± 4.6
350212.0 ± 4.9
649231.4 ± 5.5

References

  1. Aoki M, Suzuki O. 2005. Predicting time of parturition from changing vaginal temperature measured by data-logging apparatus in beef cows with twin fetuses. Anim. Reprod. Sci. 86:1-12.
    Pubmed CrossRef
  2. Chesney KL, Bryda EC. 2020. Using vaginal impedance measurement to identify proestrus in rats given luteinizing hormone releasing hormone (LHRH) agonist. J. Am. Assoc. Lab. Anim. Sci. 59:282-287.
    Pubmed KoreaMed CrossRef
  3. Choi W, Ro Y, Hong L, Ahn S, Kim H, Choi C, Kim D. 2020. Evaluation of ruminal motility using an indwelling 3-axis accelerometer in the reticulum in cattle. J. Vet. Med. Sci. 82:1750-1756.
    Pubmed KoreaMed CrossRef
  4. Glencorse D, Bathgate R. 2023. Vaginal and vestibular electrical resistance as an alternative marker for optimum timing of artificial insemination with liquid-stored and frozen-thawed spermatozoa in sows. Sci. Rep. 13:12103.
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