ECP vs. GnRH in Controlled AI Programs

More than 25% of cows are anestrous (not cycling) at the beginning of the breeding season. The use of estrogen to induce estrus has been a tool available for more than 50 years, but has not been widely used. Jeff Stevenson, Kansas State University (K-State), told attendees of the National Association of Animal Breeders (NAAB) reproductive symposium that his and other research has shown estrogen can be an alternative to GnRH for upfront follicle control, but it may not be as effective in anestrous cows. 

The only estrogen product approved for use in cattle is estradiol cypionate (ECP). Its label indicates therapeutic usage to correct anestrus in the absence of follicular cysts.

To replace GnRH, Stevenson said estrogen must 
• induce upfront follicle turnover in a synchronization program in cycling cows;
• induce upfront ovulation in anestrous cows;
• induce ovulation after PGF; and
• be easy to administer.
It must not produce “hyper-estrous” activity, which can lead to injury of cows caused by excessive riding and standing behavior.

Research conducted at K-State showed that using ECP instead of GnRH reduces the need to remove calves for 48 hours prior to timed breeding. If using ECP with CIDR, Stevenson recommends removing the insert after nine days (rather than seven) because of the delayed follicle development seen with ECP use.
 
Stevenson said producers may want to consider resynchronization of estrus after timed AI breeding. On Day 13 after timed AI, producers can administer ECP, then reinsert a CIDR for seven days, followed by a second ECP shot. This has no adverse effect on established pregnancies and does synchronize repeat estrus. Research to date has shown the practice (using a 0.5-mg dose) reduced conception rates in heifers. In suckled beef cows resynchronization produced normal conception rates when ECP and CIDRs were used.

The NAAB symposium preceded the 35th annual meeting of the Beef Improvement Federation (BIF) May 28-31, 2003, in Lexington, Ky. To access the proceedings paper or the audio of Stevenson’s presentation, visit the newsroom.

— by Angie Denton