Artificial insemination (AI) is great technique to incorporate superior genetics into a cow herd. High accuracy genetics are available from multiple bull semen companies. One of the most popular uses of artificial insemination and estrous synchronization is in breeding heifers to high growth calving ease bulls.

The Beef Reproduction Task Force is comprised of reproductive physiologists from across the United States. In addition to education, the task force publishes estrous synchronization protocols for both beef cows and beef heifers.

The beef cow protocols are arranged in three categories: Heat Detection, Heat Detect & Time AI, and Fixed-Time AI. (Bos Indicus cows have a separate protocol.) Protocols run from 8 to 13 days, with drugs administered at prescribed times.

These protocols can be found online at Beef Reproduction Task Force (http://beefrepro.org). Click on ‘Protocols’ and select either ‘Conventional semen’ or ‘Sexed semen’ for the appropriate protocols.

All protocols use various combinations of GnRH (gonadotropin releasing hormone), prostaglandin (PGF2 alpha) and CIDRs.  CIDRs contain a progesterone hormone to delay cows from coming into heat.  GnRH stimulates ovulation and prostaglandin regresses the corpus luteum which leads to cows coming into heat.

For beef cows, the 7-day CO-Synch + CIDR is popular for timed AI breeding. On Day 1, GnRH is injected and a CIDR is inserted within the cow’s vagina.  On Day 7, the CIDR is removed and prostaglandin is injected. Between 60 and 66 hours after CIDR removal, GnRH is again injected and the cow is inseminated. Successful pregnancy rates with Timed AI are between 50- 65%. Higher conception rates involve strict adherence to protocols, cows in good body condition and health, and excellent AI technique.

Beef heifers have similar synchronization options with an additional drug option of using MGA in place of the CIDR. MGA is fed daily and feed intake must be even across all heifers. A popular synchronization protocol is the long-term timed protocol using MGA and prostaglandin. In this protocol, MGA is fed for 14 days. At 19 days after the last MGA feeding, the heifers are injected with prostaglandin and then 66 hours later the heifers are injected with GnRH and inseminated. This long-term protocol takes 33 days from start to AI.

A short-term protocol for heifers is the 7-day CO-Synch + CIDR.  From start to AI, this short-term protocol takes 9 days and requires moving cattle through a chute on Days 0, 7 and 9 for a total of three visits to the chute. 

Visit with your AI technician and your bull semen salesperson. They can provide insight into techniques that work for them in obtaining high conception rates with Timed AI.

Karl Hoppe
Karl.Hoppe@ndsu.edu
Extension Livestock Systems Specialist