Ovarian profile and pregnancy rates following ovulation synchronization and timed-artificial insemination in dairy cows

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Published on: August 13, 2020

a Megan Bollman, b Ashley Greenhawk, b Ann Shipley, a Philippa Gibbons, a John Gibbons

a College of Veterinary Medicine, Lincoln Memorial University, Harrogate, TN 37752, b Hickory Corner Dairy, Speedwell, TN 37870


In the dairy reproduction industry, determining the precise timing for artificial insemination (AI) is a crucial component in obtaining a successful pregnancy outcome. The detection of estrus in dairy cattle is typically characterized by visible behavioral signs such as increased activity and vocalization, aggressive behavior, mounting, and standing to be mounted (Reith & Hoy, 2018).  Recognition of estrus has historically been difficult due to behavioral variability among individual animals and environment. The appearance and duration of estrus can be influenced by high milk yield, inadequate nutrition, stress, and overall welfare of an individual animal (Nowicki, Baraniski, Baryczka, & Janowski, 2017).  It is also time consuming and expensive for farm staff to monitor the herd for these behavioral signs. Recognition of estrus still remains low even though reproduction management technology strategies, i.e. pressure sensing systems, video cameras, activity meters; have been implemented to ease the task of visually identifying estrus in dairy cattle, (Reith, & Hoy, 2018). Previous studies have shown that a range of 50% of cattle in estrus exhibiting behavioral signs were identified with visual observation to 70% of cattle in estrus were identified using an activity monitoring system (Carvalho et al., 2014). Without the proper technology or technique for estrus detection, strategies to adequately time artificial insemination continue to be a challenge to the dairy industry.

Newer technologies such as timed artificial insemination has been widely used following the synchronization of ovulation in dairy cattle (Wiltbank, & Pursley, 2014). Ovulation synchronization eliminates the need to recognize estrus prior to artificial insemination. Since its introduction in 1995 Ovsynch® and its newer modifications, Presynch-Ovsynch® and Double-Ovsynch®, have almost replaced estrus detection in many dairy herds (Carvalho et al., 2014). By manipulating hormones in order to synchronize ovulation, the challenges of visual estrus identification are reduced, and the number of dairy cattle serviced through timed artificial insemination is increased (Nowicki, Baraniski, Baryczka, & Janowski, 2017). Ovsynch® and its modified protocols may be useful to improve reproduction performance in dairy cattle as it facilitates by appointment breeding and some dairy cows that showed no signs of estrus will indeed be serviced and become pregnant.

The focus of this case study was to evaluate the hormonal response of a dairy herd by observing their ovarian structures following a modified Ovsynch® protocol.  The ovarian structures were observed on the day of insemination and retrospectively correlated to pregnancy outcome.


A modified Ovsynch® protocol was implemented at a large (≈ 700 cows) local dairy, and is illustrated in Figure 1.  Data was collected from lactating dairy cattle from November 28th, 2018 through May 24th, 2019.

On the day of AI, transrectal ultrasonography was conducted to observe ovarian structures. Follicular and corpora lutea (CL) structures were visualized measured and data recorded to retrospectively relate ovarian structures with the pregnancy status on Day 35 post AI. Insemination was conducted regardless of ovarian status, by a single technician using commercially available frozen semen. On Day 35 after AI, transrectal ultrasonography was again used to observe the presence of uterine fluid, ovarian structures, abnormal findings, and to detect the presence of a viable fetus

Results and Discussion:

A total of 60 out of 148 lactating dairy cattle that were analyzed successfully became pregnant following a modified Ovsynch® protocol, giving an overall pregnancy rate of 40.5 ± 0.04% (Table 1). However, the diameter of the largest follicle was not significantly different (P>0.05) between those cows that became pregnant (18.0 ± 0.6mm), and those that did not become pregnant (18.1 ± 0.5mm). Putative cystic cows (largest follicle > 30 mm) were excluded from this analysis; however, 3 of the 6 cows considered to be cystic but were inseminated became pregnant (Largest follicle diameter = 35.3 ± 0.9 versus 40.0 ± 5.0 mm, pregnant versus open). The presence of CL structures in cattle that became pregnant and cattle that did not become pregnant was similar (P>0.05; 25.0 and 29.5%, respectively; Table 1). The diameter of the CL was also similar (P>0.05) between those cows that became pregnant, and those that did not (17.3 ± 1.3 and 16.7 ± 1.0mm, respectively; Table 1).

The average diameters of the ovarian structures (Follicles =18mm, CL =17mm) in lactating dairy cows that became pregnant verse those that did not were further investigated.  In a higher (P=0.056) percentage of pregnant cows, the diameter of the largest follicle was ≤18mm (65.0 ± 0.1%) compared to those cows in which the largest follicle was >18mm (35.0 ± 0.1%; Table 2).  Although numerically superior, there was no statistical difference in the percentage of pregnant cows with a CL diameter of <17mm (60.0 ± 0.2%) compared to those with a CL >17mm (40.0 ± 0.1%; Table 2).

There was a trend (P=0.131) for a higher percentage of the non-pregnant cows to have a diameter of the largest follicle ≤18mm (55.7 ± 0.1%) compared to those in which the largest follicle >18mm (44.3 ± 0.1%; Table 2).  There was no statistical difference in the percentage of non-pregnant cows with a CL diameter of <17mm (52.0 ± 0.1%) compared to those with a CL >17mm (48.0 ± 0.1%; Table 2).


The use of timed artificial insemination programs and transrectal ultrasonography are beneficial in reproduction management strategies (Colazo, & Mapletoft, 2014). Ovulation synchronization in lactating dairy cows has continued to be an efficient management tool in the dairy reproduction industry. The analysis of ovarian structures following a modified Ovsynch® protocol was useful but not absolute in predicting which cows would become pregnant and which would not.  This study determined that although the diameter of the largest follicle in dairy cows at AI did not influence pregnancy rate, a higher percentage of cows that became pregnant had smaller follicles (≤18mm).  Any effects of the presence or diameter of the CL on pregnancy status was apparently outweighed by other factors.  Further, it is unclear whether the cows that did not become pregnant failed to respond to the synchronization process or were influenced by these factors (nutrition, stress, lactational status, body condition, genetics, etc.).  In addition to evaluating overall reproductive health, trans-rectal ultrasonography may be a useful tool for predicting pregnancy outcome.  Further research is required to evaluate a more robust ovarian classification system or to evaluate of the endocrine status at the time of AI may also be useful to determine which dairy cows will likely become pregnant or not following Ovsynch® and AI.


The Authors appreciate the assistance and access to the lactating dairy cows provided by Hickory Corner Dairy, Speedwell, TN


Carvalho, P.D., Guenther, J.N., Fuenzalida, M.J., Amundson, M.C., Wiltbank, M.C., Fricke, P.M. (2014). Presynchronization using a modified Ovsynch protocol or a single gonadotropin-releasing hormone injection 7 d before an Ovsynch-56 protocol for submission of lactating dairy cows to first timed artificial insemination. Journal of Dairy Science. 97(10), 6305-6315. Retrieved from: https://www.sciencedirect.com/science/article/pii/S0022030214005244#bib0210

Colazo, Marcos G., & Mapletoft, Teuben J. (2014). A review of current timed-AI (TAI) programs for beet and dairy cattle. The Canadian Veterinary Journal. 55(8), 772-780. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4095965/

Nowicki, A., Baraniski, W., Baryczka, A., & Janowski, T. (2017). Ovsynch protocol and its modifications in the reproduction management of dairy cattle herds-an update. Journal of Veterinary Research. 61(3), 329-336. Retrieved from https://content.sciendo.com/view/journals/jvetres/61/3/article-p329.xml

Reith, S., & Hoy, S. (2018). Review: Behavioral signs of Estrus and the Potential of Fully Automated systems for Detection of Estrus in Dairy Cattle. NCBI 12(2), 398-407. Retrieved from https://pubmed.ncbi.nlm.nih.gov/28807076/

Wiltbank, Milo C., & Pursley, Richard J. (2014). The cow as an induced ovulatory: Timed AI after synchronization of ovulation. Theriogenology 81(1), 170-185. Retrieved from https://www.sciencedirect.com/science/article/pii/S0093691X13003828

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