Increasing conception rate by addition of a second prostaglandin injection in an Ovsynch and progesterone treatment programme for dairy cows not detected in oestrus before the start of the seasonal mating period

ABSTRACT

Aims

To assess the effect on conception rate to first service, 3- and 6-week in-calf rates, final pregnancy rate and the hazard of pregnancy, of addition of a second prostaglandin (PG) injection 24 hours after the first, in a synchrony programme combining Ovsynch and progesterone in pasture-based dairy cows that had not been detected in oestrus before the start of the seasonal mating period.

Methods

This prospective, negative-controlled study was conducted using anoestrous cows (n = 1,411) from nine spring-calving dairy herds in the Waikato region of New Zealand. Ovaries of cows not detected in oestrus were examined by transrectal ultrasonography and the presence of a corpus luteum determined. All cows were then treated with an intravaginal progesterone-releasing device and injected I/M with gonadorelin (Day −9). Cows were injected I/M with cloprostenol at device removal (Day −2) and on Day −1 were injected with either water (single PG; n = 720), or cloprostenol (double PG; n = 692). On Day 0 cows were injected again with gonadorelin, unless previously detected in oestrus, and were inseminated on Day 1. Based on dated pregnancy diagnosis by transrectal ultrasonography, cows were categorised as conceiving to first insemination, becoming pregnant in the first 3 or 6 weeks, or becoming pregnant by the end of the mating period.

Results

Cows in the double PG group had increased conception rate to first service (45.3 (95% CI = 45.1–45.4)% vs. 41.1 (95% CI = 41.0–41.3)%; p < 0.001), 3-week in-calf rate (53.4 (95% CI = 53.6–54.0)% vs. 49.2 (95% CI = 49.0–49.4)%; p < 0.001), and 6-week in-calf rate (67.2 (95% CI = 65.7-68.8)% vs. 63.5 (95% CI = 62.0-65.0)%; p = 0.014) compared to cows in the single PG group. Final pregnancy rate and hazard of pregnancy did not differ between treatment groups (p >0.2).

Conclusions

Addition of a second PG injection 24 hours after the first, increased conception rate to first service and the proportion of cows pregnant by 3 and 6 weeks after commencement of the mating period.

Clinical relevance

Improved outcomes can be achieved when treating those cows not detected in oestrus by the start of the seasonal mating period by addition of a second PG injection to the currently recommended treatment protocol for these animals.

KEYWORDS:

• Anoestrus
• prostaglandin
• treatment
• dairy cows
• dose
• conception rate

Acknowledgements

The cooperation of the herd owners and staff is gratefully acknowledged. The assistance of the field technicians of Cognosco including Bev Brownlie, Tina Chapman, Kelly Collier, Anna Maisey, Jacqui Tyler, Megan Whitwam, Eve Wilkes, Kerry White, and Cathy Yanez is gratefully acknowledged. Ovarian ultrasonography was undertaken by veterinarians of Anexa FVC including Julia Baynes, Sarah Clarke, Alison Cullum, Steve Harkness, Finley Koolhoven, and Mike Shallcrass. This study was funded by Bayer Animal Health New Zealand Limited.

Notes

1 https://doi.org/10.1080/00480169.2021.1906343

2 https://doi.org/10.1080/00480169.2021.1906343

3 https://doi.org/10.1080/00480169.2021.1906343

4 https://doi.org/10.1080/00480169.2021.1906343

5 https://doi.org/10.1080/00480169.2021.1906343

Additional information

Funding

This work was supported by Bayer Animal Health NZ Ltd [grant number 4501875290].