Vet Column 7-12-10 | TheFencePost.com

Vet Column 7-12-10

David L. Morris, DVM, Ph.D.
Fort Collins, Colo.

Finding protocols that are practical to implement, affordable to use, and result in acceptable pregnancy rates after treatment administration succinctly summarize goals needed to support increased adoption of artificial insemination (AI) of beef cows. Multiple treatment options exist to alter the estrous cycle of beef cows to facilitate AI whether one chooses to observe for heat following treatment to determine insemination time or utilize fixed-time AI. Genetic advancement through use of AI continues to be one of the most cost-effective choices among the assisted reproductive technologies available for use.

One of the more recent products available for use to synchronize heat, and subsequently ovulation (release of the egg from the ovary), is the controlled internal drug release (CIDR) insert product. Several protocols involving this progesterone releasing device have been developed for both heifers and cows. One of the issues involving use of the CIDR is how long to leave the device in the female. Many suggest a seven-day placement, and more recently, some evidence has surfaced to indicate that a five-day insertion time may be workable in beef cows.

Investigators from the University of Missouri recently published data comparing the use of a seven-day CIDR insertion period with a five-day CIDR insertion period on subsequent follicle development, timing of the resulting heats displayed, and pregnancy rates after the synchronized period. As well, they also looked at using timed-AI at 66 hours following the seven-day protocol versus using timed-AI at 72 hours following the five-day protocol.

Beef cows assigned to the seven-day protocol (59 head) received 100µg gonadotrophin-releasing hormone (GnRH) (Cystorelin) intramuscularly and CIDR inserts (1.38 g progesterone) on day zero; and 25 mg of Lutalyse intramuscularly along with CIDR removal on day seven. Beef cows assigned to the five-day protocol (58 head) were administered 100µg gonadotrophin-releasing hormone (GnRH) (Cystorelin) intramuscularly and CIDR inserts (1.38 g progesterone) on day zero; 25 mg of Lutalyse intramuscularly along with CIDR removal on day five; and a second dose of 25 mg of Lutalyse intramuscularly 12 hours following the CIDR removal. Cows assigned to the seven-day protocol (209 head) (64 percent cycling at the time of treatment initiation) were inseminated 66 hours following CIDR removal and cows assigned to the five-day period (210 head) (70 percent cycling at the time of treatment initiation) were inseminated 72 hours following CIDR removal. All cows artificially inseminated received 100µg gonadotrophin-releasing hormone (GnRH) (Cystorelin) intramuscularly at the time of insemination.

In comparing the seven-day protocol and five-day protocol described, there was no difference in the number of beef cows displaying heat after treatment (85 percent and 79 percent, respectively); the time following treatment to come into heat (65 hours and 71 hours following Lutalyse, respectively); or the conception rates resulting from AI based upon heat detection (72 percent and 72 percent, respectively). For those cows bred by fixed-time AI as described above, there was no difference between treatment (67 percent and 67 percent, respectively); technician performing the AI; or sire used.

In this study, either treatment for synchronizing heat and ovulation in post-partum beef cows was equally effective. Beef producers, however, must be careful to consider the increased labor and treatment costs associated with the five-day protocol.