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:

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.

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:

--Scott B. Laudert, Ph.D.