Control of Estrus in Beef Heifers and Cows
by Troy Smith, field editor
DES MOINES, Iowa (Sept. 7, 2016) — “In my opinion, aside from the opportunity for genetic improvement through synchronized artificial insemination (AI), the biggest benefit is improved reproductive management.”
So said University of Missouri animal scientist David Patterson during the Applied Reproductive Strategies in Beef Cattle symposium hosted Sept. 7-8 in Des Moines, Iowa. Patterson called estrus synchronization an effective means of increasing the proportion of females that become pregnant early.
According to Patterson, effective estrus synchronization programs offer the following advantages:
- 1) cows or heifers are in estrus at a predicted time, which facilitates AI, embryo transfer (ET) and other assisted reproductive techniques;
- 2) the time required for detection of estrus is reduced, thus decreasing related labor expense;
- 3) AI becomes more practical, enabling producers to utilize genetically superior, high-accuracy sires; and
- 4) females deliver earlier in the calving season, producing calves that are older and heavier at weaning.
Patterson discussed methods to control estrus in heifers utilizing the feeding of melengestrol acetate (MGA) to suppress estrus and prevent ovulation. He emphasized that consistency of MGA intake is the key to successful application of these heifer-synchronization protocols. He stressed the importance of adequate bunk space and adherence to a feeding schedule to promote a correct level of consumption.
Citing the Missouri Show-Me-Select Replacement Heifer Program as an example, Patterson noted the increased producer interest in use of protocols for fixed-time AI. He recommended prebreeding evaluation of replacement heifer candidates and reproductive tract scoring, as is required of all Show-Me-Select heifers. The reproductive tract scoring system uses a scale from 1 to 5, where 1 is infantile, 2 and 3 are noncycling/prepubertal; and 4 and 5 are cycling/pubertal. The scoring system can be used as a tool to assist producers and their veterinarians in identifying likely candidates (higher scores) for fixed-time AI and choose an appropriate synchronization protocol.
Shifting the discussion to methods of controlling estrus in cows, Patterson described options for synchronization of estrus in cycling females, and induction of estrus accompanied by ovulation among cows that have not returned to estrus after calving. He called management on non-cycling cows one of the challenges to success with synchronized AI.
“A primary advantage in administering a CIDR (controlled internal drug release device)-based protocol in postpartum beef cows lies in the fact that these protocols not only facilitate estrus synchronization and AI in cyclic cows, but offer the added benefit of induced estrous cyclicity in anestrous cows following treatment,” said Patterson.
As with heifers, explained Patterson, application of fixed-time AI among cows affords savings in labor and time. He emphasized how stacking reproductive and genetic technologies (fixed-time AI and high-accuracy sires) has become an effective means of achieving more rapid progress in a breeding program.
“The protocols work,” stated Paterson. “These opportunities to effectively synchronize estrus and ovulation in an AI program and use of superior, high-accuracy sires opens the door for beef producers across the U.S. to take more aggressive control of their breeding programs.”
Patterson spoke during Wednesday’s ARSBC session focused on the basics of reproduction. Visit the Newsroom at www.appliedreprostrategies.com, which features comprehensive coverage of the symposium, to view his PowerPoint, read the proceedings or listen to the presentation. Compiled by the Angus Media editorial team, the site is made possible through sponsorship by the Beef Reproduction Task Force.