ARSBC 2018: Control of Estrus and Ovulation in Beef Cows and Heifers

David Patterson
University of Missouri

The goals of developing FTAI protocols:

• Easy to schedule and administer
• Reduce animal handling
• Result in a highly synchronized and fertile estrus and ovulation

Protocols in Heifers
Make sure you are using the protocols for the current year. Don't use protocol sheets that are several years old, as the protocols are changed and improved.

"With an MGA program, intake is key" Patterson said. He does not recommend top dressing the MGA, but mixing it into a 3 to 5 lbs carrier.

MGA has a much broader distribution of the timing of estrus expression compared to a 14-day CIDR protocol.

With a MGA protocol, you AI 72 hours after PGF2 administration. With a CIDR protocol, heifers are AI'ed 66 hours after PGF2 administration.

You should not see any estrus expression during MGA feeding periods. If you do see heifers in heat, then there is a problem with MGA intake.

Prior to the first breeding season, there needs to be heifer management.
A health program is an important part of this. Another important part is the prebreeding exam. The prebreeding exam includes weight, pelvic area and reproductive tract score (RTS). Reproductive tract scores are a 1 to 5 scoring system of the puberty status of a heifer. A score of 1 is infantile, these heifers are typically not successful in a breeding program. Heifers with a score of 4 or 5 have reached puberty.
Reproductive tract scores should be collected 4 to 6 weeks prior to the start of the breeding season.

In the Show-Me-Select Program, we are seeing an advantage in pregrancy rates when using the 14-day CIDR protocol.

Protocol compliance is key to having a successful AI program.

Protocols in 2-year Old Cows
If you use the 14-Day CIDR-PG protocol in 2-year old cows, you will see a dramatic decrease in heat expression compared to the 7-Day Co-Sync CIDR protocol. However, the pregnancy rates between these two protocols are nearly identical.

Fixed Time AI in Cows
Does the timing of insemination really matter?
Patterson's group ran an experiment in which one group of cows was AI at 54 hours and another group was AI'ed at 66 hours. AI at 66 hours gave higher pregnancy rates, highlighting how important it is to follow the protocols.
Cows that were fix time AI'ed at 54 hours, only 26% had exhibited estrus. The cows in the 66 hour group, 50% had exhibited estrus.

There is perhaps a 3% improvement with the 5-Day protocol compared to the 7-Day protocol in beef cows. However, there are higher labor and time requirements with the 5-Day protocol.

Can fertility be improved with a split-time AI approach? Split-time approach means that you delay artificial insemination of those cows that have not expressed estrus at the fixed-time AI time and delaying insemination by 20 to 24 hours.

It is not necessary to administer GnRH to those heifer or cows that have expressed estrus prior to the fixed artificial insemination time. By using split-time approach you need to use much less GnRH.

See ARSBC Newsroom for more information. http://www.appliedreprostrategies.com/2018/newsroom.html

Note: this post was live blogged and may contain errors.