Control of Estrus in Heifers
MU’s David Patterson reviews characteristics of MGA®- and CIDR®-based heat synchronization protocols for heifers.
SIOUX FALLS, S.D. (Dec. 3, 2012) — Heifers that conceive earlier in their first breeding season stay in the herd longer and produce more pounds of beef in the long run, said David Patterson, professor of animal science at the University of Missouri–Columbia (MU). Patterson was charged with discussing the control of estrus in heifers at the 2012 Applied Reproductive Strategies in Beef Cattle (ARSBC) symposium in Sioux Falls, S.D.
Patterson reviewed considerations for heifer management as it pertains to synchronization success. Prebreeding evaluation, he said, should include target weight at a year of age, reproductive tract score (RTS) and pelvic measurement.
Tract scores can be a significant aid in evaluating heifers going into synchronization programs, Patterson emphasized. “Once we have producers begin using this system, their success rates with synchronization have increased remarkably.”
Patterson said producers should be aware that exposure to implants during the suckling phase can significantly affect reproductive development of heifers, slowing glandular development in the uterus. He recommended RTS be taken four to six weeks before the breeding season to give producers time to make adjustments if needed. Heifers are ready to go on a synchronization program when 50% or more of the heifers are scoring 4 to 5.
“Why use synchronization?” Patterson asked.
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Table 1: Reproductive tract score (RTS) summary.
“When heifers become pregnant is a big deal,” he answered. Patterson noted that we have tools available to help facilitate earlier conception dates. Those tools are in the form of progestin-based products, either MGA or CIDR.
According to the National Animal Health Monitoring System (NAHMS) survey conducted in 2008, the reasons U.S. beef producers cite for not using this reproductive technology are time/labor and cost. Patterson said in his area of the country more people want to move toward timed artificial insemination (TAI) programs.
He reviewed many of the protocols developed for synchronization of estrus in heifers, beginning with the MGA-prostaglandin protocol developed by Ken Odde. The protocol calls for feeding MGA for 14 days, waiting 17-19 days and administering a shot of prostaglandin (PG). For programs using natural service, Patterson reminded that the estrus expressed three to five days after withdrawal of MGA is a sub-fertile estrus, so bulls should be turned out afterward —about 10 days after MGA withdrawal.
Patterson said heifers synchronized with MGA and PG in combination will display heat within a three- to five-day period. However, if you use MGA and bypass the PG shot, the heifers will come into heat during a 7- to 10-day period. “That’s advantageous in a lot of respects for bulls that are going into synchronization programs,” said Patterson.
Another topic Patterson felt was important to discuss was what happens to females that are placed in backgrounding yards then, at last moment, are pulled out of MGA-feeding and are bred. The study compared heifers fed MGA for 87 days vs. the standard 14 days. Once heifers were taken off MGA they received an injection of PG 17 days later. Heifers that failed to respond were re-injected 11 days later.
Results indicated that after the first injection there was an advantage to the short-term feeding program, but after the second injection results evened out. Scanning the ovaries by ultrasound revealed no abnormalities for heifers in the short-term MGA group, but 37% of those fed MGA long term had luteinized follicular cysts. In addition, some heifers actually began lactation. Conception rates and pregnancy rates were comparable for the two groups.
Patterson walked attendees through a large study comparing the 14-day MGA feeding program to the 14-day CIDR-PG protocol. Results concluded that estrous response and synchrony of estrus were significantly improved among heifers assigned to the 14-day CIDR-PG protocol. Pre-synchronization with a 14-day CIDR followed 16 days later with PG provides an effective alternative for the use in synchronizing estrus in replacement heifers. There were no differences between treatments for synchronized conception or pregnancy rates.
Patterson also discussed a multi-state CIDR trial by Cliff Lamb et al. (2006) comparing heat detection vs. TAI and various timing for administration of PG, GnRH and breeding. GnRH at CIDR insertion did not improve pregnancy rates after TAI and did not alter the percentage of heifers detected in estrus or the distribution of estrus after PG. Patterson noted that a combination of detecting estrus and AI before cleanup AI enhanced pregnancy rates over TAI.
A Missouri study comparing a seven-day CO-Synch + CIDR insertion to 14-day CIDR with GnRH between CIDR removal and PG. Essentially, the longer-term protocol outperformed the shorter protocol when heifers were time-bred.
Administration of GnRH following CIDR removal in the CIDR Select protocol is not required to facilitate synchrony of estrus, Patterson said.
Comparing the protocols in TAI systems, pregnancy rates tended to be higher for 14-day CIDR-PG compared to CIDR Select-treated heifers. Final pregnancy rates didn’t differ.
Click here to review the synchronization protocols for heifers recommended by the Beef Reproduction Task Force.
Patterson spoke during Monday's ARSBC session focused on the importance of estrus. For more information, visit the Newsroom at www.appliedreprostrategies.com to listen to his presentation and to view his PowerPoint slides and proceedings paper.
Comprehensive coverage of the symposium is available online at www.appliedreprostrategies.com. Compiled by the Angus Journal editorial team, the site is made possible through sponsorship by the Beef Reproductive Task Force and LiveAuctions.tv.
Editor's Note: This article was written under contract or by staff of the Angus Journal. To request reprint permission and guidelines, contact Shauna Rose Hermel, editor, at 816-383-5270.