Recent Developments in Estrus Synchronization Protocols

By Pedro Fontes, Assistant Professor and Extension Specialist, University of Georgia

The 2023 sire directories from cattle genetics companies are now available to cattle producers. In addition to including a wide variety of new sires, these directories also include updated estrus synchronization protocol sheets that contain both old and new protocols that have been validated and are endorsed by the Beef Reproduction Task Force (beefrepro.org). This article will provide an overview of the 7&7 Synch protocol, which was recently added to the list of protocols for use with conventional (not sexed) semen, and summarizes the research that evaluated this protocol in controlled settings.

What is Different About the 7&7 Synch?

The newly added protocol, the 7&7 Synch, can be utilized for both heifers and cows and is an adaptation of the industry-standard 7-day CO-Synch + CIDR protocol. The only difference is that the 7&7 Synch requires an additional presynchronization step a week earlier (Figure 1).

What is the Physiological Basis of the 7&7 Synch?

One of the main limitations of short-term estrus synchronization protocols is the decreased proportion of females that respond to the first GnRH injection when they are at random stages of the estrous cycle. The goal of the GnRH injection at the beginning of an estrus synchronization protocol is to induce ovulation in as many cows as possible in order to induce synchronized follicular development across the cow herd. Research indicates that only approximately 60 percent of cows and 40 percent of heifers respond to the initial GnRH injection. To overcome this limitation, a presynchronization strategy can be utilized. Presynchronization is the administration of specific hormones prior to the initiation of an estrus synchronization protocol, to increase the proportion of females that are at an ideal stage of their cycle when the first GnRH is administered. This results in a greater response to the initial GnRH injection, leading to improvements in subsequent follicular development and fertility. This is not a novel concept in cattle reproduction. In fact, the dairy industry has been utilizing protocols that include presynchronization steps for several years. Nevertheless, the adoption of presynchronization strategies has been slower in the beef industry, largely due to the extra handling that is required, which is inconvenient in more extensive beef operations.

Treatment Schedule of the 7&7 Synch

Cows or heifers receive a prostaglandin F2α injection on the first day of the protocol (Day 0), and at the same time, a CIDR device is inserted. Seven days later (Day 7), a GnRH injection is administered and the CIDR device remains in place. On Day 14, the CIDR is removed and a second prostaglandin F2α injection is administered. Heifers are artificially inseminated 54 hours after CIDR removal and cows are artificially inseminated 66 hours after CIDR removal. Therefore, the 7&7 Synch requires four trips to the chute.

Are There Improvements in Fertility to FixedTime Artificial Insemination in Controlled Research Studies?

Replacement Heifers

Initial research has shown greater estrus expression in replacement heifers exposed to the 7&7 Synch protocol when compared with heifers exposed to the 7-day CO-Synch + CIDR. Moreover, heifers exposed to the 7&7 Synch had approximately 10 percent greater conception rates compared with heifers exposed to the 7-day CO-Synch + CIDR (Figure 2; Oosthuizen et al., 2020; Mercadante et al., 2022). No controlled comparisons have been made between the 7&7 Synch and the 5-day CO-Synch + CIDR or the 14-day CIDR-PG protocol for fixedtime artificial insemination in heifers.

Postpartum Cows

Research has also evaluated the 7&7 Synch in postpartum cows. All studies have consistently reported an increase in estrus expression in cows exposed to the 7&7 Synch when compared with the 7-day CO-Synch + CIDR. Nevertheless, out of the two large-scale experiments conducted comparing these protocols, one study reported a greater conception rate in the 7&7 Synch (Anderson et al., 2022), whereas the other study reported no differences between the two protocols (Pancini et al., 2022). A third study compared the 7&7 Synch with the PG 6-day CIDR protocol (a protocol that also makes use of presynchronization) when using fixed-time artificial insemination and reported no differences in conception rates between the two protocols (Ketchum et al., 2022). Collectively, no studies reported a decrease in pregnancy rates when the 7&7 Synch was utilized.

Can This Protocol be Utilized for Embryo Transfer Recipients?

A study comparing the 7&7 Synch with the 7-day CO-Synch + CIDR in embryo recipients showed an increase in estrus expression; however, no differences in conception rates were observed (Bonacker et al., 2020). To my knowledge, no large-scale studies have compared the 7&7 Synch and the 7-day CO-Synch + CIDR solely in fixed-time embryo transfer programs (without estrus detection). Hence, the 7&7 Synch can be utilized in embryo transfer programs to increase the proportion of recipients expressing estrus. This increase in estrus expression might result in greater number of pregnancies, depending on the criteria for embryo recipient selection. However, research indicates that conception rates are similar within the females that received an embryo (Bonacker et

P. L. P. Fontes, S. Johnson, M. P. Owen, K. M. Harvey, A. F. Summer, G. A. Perry. 2022. Evaluation of Two Beef Cow Fixed-time AI Protocols That Utilize Pre-synchronization. J. Anim. Sci 100:139-140.

V. R. G. Mercadante, G. C. Lamb, N. Oosthuizen, N. W. Dias, S. Pancini, H. Haines, J. Currin, S. Clark, J. L. Stewart, G. J. Pent, M. P. Holton, D. D. Davis, S. R. Hernandez, R. L. Stewart, P. L. P. Fontes. 2021. Estrus Response and Pregnancy Rates of Beef Replacement Heifers Enrolled in Two Fixed-time Artificial Insemination Protocols, with or Without Pre-synchronization. J. Anim. Sci. 99:125–126.

N. Oosthuizen, P. L. P. Fontes, K. Porter, G. C. Lamb. 2020. Presynchronization with prostaglandin F2α and prolonged exposure to exogenous progesterone impacts estrus expression and fertility in beef heifers. Theriogenology. 146: 88-93.

S. Pancini, N. W. Dias, J. Currin, S. Clark, J. L. Stewart, V. R. G. Mercadante. 2022. Estrus Response and Pregnancy Rates of Beef Cows Enrolled in two Fixed-Time Artificial Insemination Protocols, with or without pre-Synchronization. J. Anim. Sci. 100:255-256.

Figure 1: Diagram of the industry-standard 7-day CO-Synch + CIDR Protocol and the 7&7 Synch. PG = Prostaglandin F2α. GnRH = Gonadotropin releasing hormone. CIDR = Controlled internal drug release insert. AI = Artificial insemination

Figure 2: Conception rates of replacement heifers (n = 1,552) using different estrus synchronization protocols (Mercadante et al., 2021).

Update

By Justin Hand

My New Year started with a bang. We had two cows go down, both hay suppliers ran short, my truck started making noises, and the weather (primarily lack of rain and then subzero temperatures) has yet to cooperate with getting any grazing planted. Now, this disaster is not an ideal way to begin a new year; and because of it, I spent the first three days of 2023 fighting-mad. I scruffed, grumbled, and was somewhat irritable – until I reflected on what the man in the pulpit said on New Year’s Day.

Sara, Della and I attend church regularly; but after an extended Christmas and New Year, our Sunday school class was canceled because we were all still scattered around with family. Honestly, we were thinking about skipping church entirely that day until Della wanted to go to her Papa’s church; we figured that it was a sign to drag ourselves out of the house and go.

For the past few years, my father has pastored Trinity Methodist Church, and in the message given on New Year’s Day, he used flying on an airplane as an analogy for the year that lay ahead. Right now, he explained, we are just boarding the plane about to take a trip, and we are entirely focused on the destination and all of the things that lie ahead of us; not for one second are we concerned or thinking about the pilot. Pilots fly planes every day; it’s their job to get people from one place to the next, and we just trust that they will get us to where we are going. He spoke for several minutes about the main Pilot in our lives, and the service was soon over. There is no added fluff or long, drawn-out stories; Randy is all about business, so his point is quickly reached.

The very next day is when things began to fall apart. I got the call about the down cows; next, the hay man told me he was out, and the catastrophes started to pile on after that. After a few days of storming around mad trying to fix this giant pile of messes, I got to thinking about what daddy had said a few days before. I soon realized that I have 362 days left in 2023, and my being mad wasn’t helping me make sound decisions or helping solve any of these problems. I asked God to help me, and I finally calmed down. Dr. Angie helped us get the cows up. We found some hay to get us by for a couple of more weeks. The truck still makes noises, and we found some old tires that we could convert to feed bunks to feed in place of the lost grazing. We all struggle to various degrees. We all know that this industry takes lots of hard work and sacrifice. All that we can do is keep trying – and trust that our Pilot will get us where we’re going.

Call me if I can help you in any way.

Board Members

Chair Zach Floyd 229-309-4714

Zacharycattle@gmail.com

Chair Elect Justin Hand 229-392-0231 jhand@uga.edu

Vice Chair Sarah Dyer 352-250-9571 Sarahdyer@uga.edu

Secretary/Treasurer George Ligon 803-389-9851 georgeligon@georgeligon.com

Region 2 Rep. Marrissa Blackwell 678-672-9946 Marrissa@uga.edu

Region 3 Rep. Greyson Fernandez 706-604-6165 greyson@ivycreekcattlecompany.com

Region 4 Rep. Cody Copelan 706-473-4757 Codycopelan@gmail.com

Region 5 Rep. Coleman Harrison 229-403-8011 charrison@gmail.com

ABAC Rep: Brennan Hart UGA Rep: Moira Taber

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