Recent research evaluated the effects of the period of follicle dominance in a timed-artificial insemination (AI) protocol and its effect on conception rate in 4,098 dairy cows.

The first experiment included 1,165 cows receiving two doses of PGF at 36 and 50 days in milk (DIM). At 61 DIM cows were randomly assigned to either Cosynch-72 (CoS72) or to a five-day CoS72 with one (5dCoS1) or two (5dCoS2) doses of PGF.

Experiment two assigned 2,933 cows randomly to CoS72 or 5dCoS2 protocols. Blood samples were taken and ovulatory response was monitored.

The results published in the July 2010 issue of the Journal of Dairy Science concluded:

 Experiment one:

The proportion of cows with corpus lutea (CL) regression at the time of AI differed at 79, 59.1, and 95.7 percent for CoS72, 5dCoS1 and 5dCoS2, respectively.

Cows that ovulated to the first GnRH of the Cosynch tended to have less of a CL regression than those that did not ovulate.

Experiment two:

CL regression was 4.8 percent less (91.5 percent vs. 96.3 percent), but detection of estrus was 7.3 percent higher for CoS72 than 5dCoS2. Cows in estrus had higher conception rates.

Conception rate was 7 percent greater for cows enrolled in 5dCoS2 than cows in the CoS72 group.

Researchers concluded reducing the time of follicle dominance in timed AI improved fertility.

Access the abstract.

Source: Dairy Cattle Reproduction Council