Editor's note: Two articles in the February issue of BEEF detailed estrus synchronization (ES) protocols in beef cattle (“Using MGA,” page 28, and “Head To Head,” page 50). Regarding the ES topic, BEEF offers the following clarification.

Extra-label use of approved reproductive drugs for ES is a challenge for practitioners and producers due to the exclusion of reproductive drugs from the regulations enacting the Animal Medicinal Drug Use Clarification Act (AMDUCA). Efforts to clarify the extra-label use of approved reproductive drugs have been hampered, as little economic incentive exists for drug companies to pursue expanded label claims on already-approved products.

Drugs currently used in beef cattle ES protocols include prostaglandin products, MGA, CIDR and GnRH products.

• Prostaglandin products are approved for use in ES protocols in beef cows and beef heifers.

• MGA is approved for use in ES protocols in beef heifers but not beef cows.

• CIDR is approved for ES use in beef cows and beef heifers.

• GnRH products are approved for use in cattle for treatment of ovarian cysts. Though GnRH products aren't specifically approved for beef cattle ES protocols, GnRH injectable products are prescription-only products and aren't of regulatory concern.

An important issue to be addressed is the complexity of ES protocols, the combination of drugs within various protocols, delivery systems, and timing of administration of integral protocol components. Numerous protocols have been published that many times are further revised to meet specific production adaptations.

Selecting a protocol can be difficult as there are many production-system variables to consider. These include economics, proper administration of each component, client compliance and Beef Quality Assurance compliance.

Sometimes, veterinarians are uninformed on these protocols, and ill equipped to help clients choose the best program. Thus, producers often turn to university researchers with specific training in ES and breeding.

However, university researchers may not be aware of laws regulating drug use in specific classes of animals. Therefore, it's important that producers, animal scientists and veterinarians work together to for the success of the breeding program and the good of the livestock industry.

There are no legal, extra-label uses of feed additives for beef cattle. The feeding of MGA is specifically approved for estrus suppression and ES in heifers only.

Though 35 years of feeding MGA to beef cows has demonstrated MGA is safe, effective and economical, the feeding of MGA to adult cows isn't an FDA-approved label claim and is thus prohibited by FDA. It's unfortunate the MGA label doesn't include all reproductively mature beef cattle, but it does not.