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Estrous Synchronization Protocol Evolution and Practical Application

RUIDOSO, NEW MEXICO (Aug. 29, 2018) — Research has led to a better understanding of methods to induce and synchronize estrus and ovulation in postpartum cows and replacement heifers, enabling cattle producers to expand their use of artificial insemination (AI). University of Missouri animal scientist Dave Patterson discussed the evolution of synchronization protocols and their practical application during the Applied Reproductive Strategies in Beef Cattle Workshop hosted Aug. 29-30, in Ruidoso, N.M.

Synchronization of mature cows is most successful, regardless of protocol, when cows have adequate body condition (minimum body condition score 5) and are at least 50 days postpartum at the time of AI, said the University of Missouri’s Dave Patterson.

According to Patterson, the objective has been to ease protocol scheduling and administration and minimize handling of cattle (trips through a chute), while achieving highly synchronized and fertile estrus and ovulation. Many protocol options exist that utilize heat detection (observed estrus) prior to insemination, or insemination of all animals at a predetermined time through fixed-time AI (FTAI).

Patterson said an important consideration, regardless of protocol choice, is whether the females are physiologically ready for synchronization. He warned against choosing replacement females from among heifers that have previously received a growth-promoting implant, citing potential for irreversible damage to the reproductive tract as a result of implants. For all chosen candidates, he advised prebreeding evaluation of age and weight plus pelvic measurement and scoring of heifer reproductive tracts according to a 5-point system (1 = infantile to 5 = mature tract and cycling).

Patterson said assignment of reproductive tract scores (RTS) provides valuable insight regarding which heifers are cycling already and those that can be expected to start soon.

“RTS timing is a big deal,” emphasized Patterson. “We recommend that evaluation and scoring be done four to six weeks before breeding, or two weeks before estrous synchronization. It will be most successful when 50% or more of the heifers have scores of 4 or 5.”

Several synchronization protocols suitable for heifers exist. Patterson explained that protocols include a progestin, administered through orally dosed melangestrol acetate (MGA), or progesterone, administered through a controlled internal drug release (CIDR®) device, which halts estrus until progestin/progesterone is withdrawn and prostaglandin (PG) is administered to induce estrus.

When comparing the MGA-based program with a long-term CIDR-based protocol, Patterson called both methods effective. However, evidence suggests a statistical advantage with regard to heat expression following treatment for the CIDR-based protocol. Therefore, Patterson recommended basing protocol choice on predetermined heifer cyclicity. He also explained that success with the MGA protocol depends on heifers consuming the correct dosage of MGA through their feed, so managers unable to carefully control consumption should consider an alternative protocol.

“In any production system, a manager will be working with cycling and non-cycling females, and there may be some advantage to using the longer, CIDR-based protocols,” said Patterson.

Patterson said that synchronization of mature cows is most successful, regardless of protocol, when cows have adequate body condition (minimum body condition score 5) and are at least 50 days postpartum at the time of AI.

Addressing the question of whether timing of insemination really matters, Patterson shared data from studies comparing CO-Synch + CIDR with FTAI at 54 hours after CIDR removal and administration of prostaglandin, vs. FTAI at 66 hours. Results showed that more cows exhibited estrus prior to FTAI when insemination was performed at 66 hours, and cows exhibiting estrus prior to FTAI had higher pregnancy rates than cows not showing estrus.

For producers considering a choice between 5-day and 7-day CO-Synch + CIDR protocols for FTAI, Patterson noted evidence of up to a 3% advantage with the 5-day protocol. However, managers should consider the increased labor and treatment costs it requires.

“The protocols work,” stated Patterson, urging managers to refer to the latest listing of recommended protocols. He emphasized that, regardless of protocol choice, success hinges on compliance with accuracy and timing of product administration and insemination.

For details on Patterson’s presentation — including the proceedings, PowerPoint and video of his presentation — visit the Newsroom at www.appliedreprostrategies.com.

Editor's Note: This article was written under contract or by staff of Angus Media. To request reprint permission and guidelines, contact the Angus Media editorial team at 816-383-5200.