Comparisons of pregnancy rates of fixed-timed artificial insemination (TAI) protocols in mature, suckled beef cows have generally favored the five-day, progesterone-impregnated, controlled internal drug release (CIDR) synchronization protocol over the seven-day CIDR program. Unfortunately, the five-day protocol is more labor intensive, which may offset the observed fertility advantages.
Kansas State University beef cow-calf researchers, in cooperation with researchers from seven other universities, studied alternatives to the five-day CIDR protocol in 591 cows from three different locations.
The critical step in the success of the five-day program is administration of a second injection of prostaglandin (PG) eight hours following CIDR removal. However, this second dose of PG requires a second trip through the chute, meaning more time and labor. Ideally, the second PG injection could be avoided.
Experimental treatments tested were:
- Two standard doses of PG injected eight hours apart following CIDR removal,
- A double-dose injection of PG at CIDR removal and
- A single-dose injection of PG at CIDR removal included as an experimental control.
All cows were TAI at 72 hours after CIDR removal; 12 days later they were exposed to cleanup bulls for an average 65-day breeding season that ranged from 45 to 96 days across the Kansas locations.
- TAI pregnancy rate (51.8%) in cows receiving the double-dose injection of PG at CIDR removal was numerically lower than TAI pregnancy rate (57.4%) in cows receiving the standard two PG injections eight hours apart.
- Cows receiving only the single-dose injection of PG at CIDR removal had the lowest TAI pregnancy rate at only 44.2%.
- Cycling cows were 1.5 times more likely to become pregnant after TAI than non-cycling cows.
- Cows three years and older were 1.6 times more likely to conceive to TAI than two-year-old cows.
Final pregnancy rate at the conclusion of the breeding season was not different between the three PG injection treatments. Overall, three-year-old-or-older cows were 3.9 times more likely to be pregnant at the end of the breeding season than were two-year-old cows (94% vs. 79%).
Researchers conclude that two doses of PG injected eight hours apart following CIDR removal are required to maximize TAI pregnancy rates of the five-day protocol.
To read the full research reports, go to:
- http://www.ksre.ksu.edu/library/lvstk2/srp1047.pdf  - page 14
- http://beefrepro.unl.edu/resources.html 
-- Scott B. Laudert, Ph.D.