Estrus Synchronization
Protocols for Heifers
by Troy Smith for Angus Productions Inc.
SAN ANTONIO, TEXAS (Jan. 28, 2010) — Addressing cattle producers gathered for the Applied Reproductive Strategies in Beef Cattle (ARSBC) workshop hosted Jan. 28-29 in conjunction with the 2010 Cattle Industry Annual Convention and NCBA Trade Show in San Antonio, Texas, University of Missouri (MU) reproductive physiologist David Patterson reviewed methods for synchronizing estrus prior to artificial insemination (AI) of breeding heifers. Patterson’s presentation focused primarily on progestins, including orally delivered melangestrol acetate (MGA) and vaginal inserts (CIDRs) used to suppress estrus prior to a planned breeding period.
Patterson said MGA-based protocols have seen more widespread use for synchronizing estrus in heifers. Used most simply with natural service, heifers are fed MGA for 14 days and exposed to bulls 10 days after withdrawal of MGA. A second method, used with AI, involves feeding of MGA and administration of prostaglandin hormone 19 days after MGA withdrawal. This treatment shortens the synchronized period and maximizes conception rate.
It is not uncommon for heifers to receive MGA for longer periods if, for example, replacements are selected from a larger group of heifers in a backgrounding program. Patterson warned that evidence suggests long-term feeding of MGA may result in higher than normal incidence of follicular cysts and reduction in estrous response after prostaglandin is administered. Re-injection with prostaglandin typically results in satisfactory breeding performance.
Patterson said a third MGA-based protocol involves injecting heifers with gonadotropin-releasing hormone (GnRH) 12 days after MGA withdrawal, followed by injection of prostaglandin in another seven days. The addition of GnRH to the protocol has been shown to increase the proportion of heifers with synchronized follicular waves at the time prostaglandin is administered.
Patterson described multiple alternatives to MGA-based protocols, which introduce progestin by inserting CIDRs for a period of seven days or for 14 days, followed by administration of prostaglandin and GnRH according to the chosen CIDR-based systems involving insemination after heat detection or timed insemination. Patterson noted that CIDR-based protocols may be applied to synchronization of mature cows as well, while MGA use is restricted to heifers.
Patterson said the various methods have been used successfully, but evidence suggests better results may be achieved with protocols involving insertion of CIDRs for the longer time period.
“Long-term CIDR-based protocols enhance synchrony of estrus, compared to short-term CIDR-based or MGA-based protocols,” Patterson stated. “Pregnancy rates resulting from fixed time AI of beef heifers are expected to be higher following treatment with long-term CIDR-based protocols because of improvements in synchrony of estrus following treatment.”
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