Estrous Synchronization Protocols for Heifers
by Barb Baylor Anderson for Angus Productions Inc.
NASHVILLE, TENN. (Aug. 5, 2010) — Producers should embrace estrous synchronization management practices for heifers. Such protocols can facilitate artificial insemination (AI) and embryo transfer (ET), reduce the time to detect estrus, induce cyclicity in peripubertal heifers and help cows conceive earlier in the breeding season, Dave Patterson, University of Missouri animal scientist, told attendees of the Applied Reproductive Strategies in Beef Cattle (ARSBC) Conference in Nashville, Tenn.
In addition, Patterson noted that females that conceived to a synchronized estrus in research calved earlier in the calving season. Weaned calves in these scenarios were, on average, 13 days older and 21 pounds (lb.) heavier than calves from non-synchronized females.
“The most recent development of convenient and economical protocols to synchronize estrus and ovulation and facilitate the use of fixed-time AI (FTAI) result in high fertility,” Patterson said. “Perhaps past failures — which resulted when females that were placed on estrus synchronization treatments failed to reach puberty or to resume normal estrous cycles following calving — limit producer use. But we need to see increased adoption of these important management practices.”
Patterson said current research has focused on development of methods that effectively synchronize estrus in replacement beef heifers and postpartum beef cows by decreasing the period of time over which estrous detection is required. The strategy facilitates use of FTAI.
“Expanded use of AI and adoption of these emerging reproductive technologies require precise methods of estrous cycle control,” Patterson said. “Effective control of the estrous cycle requires the synchronization of both luteal and follicular functions.”
Patterson quickly reviewed a number of protocols currently in use, which are detailed in his conference proceedings. He focused on efforts to develop more effective estrous synchronization protocols that synchronize follicular waves by injecting GnRH followed seven days later by injection of prostaglandin (PG products that include Ovsynch, CO-Synch or Select Synch).
“A factor contributing to reduced synchronized pregnancy rates among heifers treated with these protocols is the extreme variability in response to GnRH based on the day of the cycle GnRH is administered. Between 5% and 15% of cows treated with these protocols exhibit estrus on or before the PG injection,” he said. “New protocols for inducing and synchronizing a fertile estrus in replacement beef heifers and postpartum beef cows in which progestins are used provide new opportunities for beef producers to synchronize estrus and ovulation and facilitate FTAI.”
Overall, Patterson says data from research on the various estrus synchronization protocols for use in replacement heifers suggest that new methods of inducing and synchronizing estrus create the opportunity to significantly expand the use of AI in the U.S. cow herd.
“Improving traits of major economic importance in beef cattle can be accomplished most rapidly through selection of genetically superior sires and widespread use of AI,” he said. “Procedures that facilitate synchronization of estrus in estrous cycling females and induction of an ovulatory estrus in peripubertal heifers and anestrous postpartum cows will increase reproductive rates and expedite genetic progress. Estrous synchronization can be an effective means of increasing the proportion of females that become pregnant early in the breeding season, resulting in shorter calving seasons and more uniform calf crops.”
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