Choosing an estrus synchronization protocol that can be used with either artificial insemination (AI) or with natural service can be perplexing, as a number of synchronization protocols are available. To assist cattle producers in determining an effective estrus synchronization protocol, the Beef Reproduction Task Force provides recommendations for estrus synchronization protocols to be used in either cows or heifers and these protocol recommendations are reviewed annually by the Task Force. The current protocol recommendations are found at the Applied Reproductive Strategies in Beef Cattle website at beefrepro.org.
For synchronization protocols recommended by the Beef Reproduction Task Force, it is suggested that mature cows be in a body condition score (BCS) 5 or greater and at least 50 days or more postpartum at the time of insemination. Recent studies suggest that beef heifers with a body condition score of 6 and reproductive tract score greater or equal to 4 are more likely to become pregnant to AI.
Three primary groups of products are used to synchronize estrus or ovulation in beef cattle: prostaglandin F2? (PG); progestins (progesterone); and gonadorelins (gonadotropin-releasing hormone or GnRH). Producers should visit with a veterinarian about the products used for synchronization as a current veterinary-client-patient-relationship (VCPR) will be necessary before these products can be purchased. In all cases, be sure to use the correct synchronization product at the recommended time and follow Beef Quality Assurance practices when administering the products.
When trying to decide which protocol to use, one must remember that there are protocols that will synchronize estrus (standing heat) which are designed to synchronize the expression of behavioral estrus into a three-to-seven-day time period. There are other protocols that will synchronize ovulation within estrus; these protocols are used for fixed-time AI (FTAI). FTAI protocols do allow the producer to utilize a limited estrus detection protocol or a no-estrus detection protocol.
The use of sexed semen can result in a decreased conception rate when compared to the use of conventional semen used in similar conditions and situations. Sexed semen can be used on any female observed in estrus (standing heat) and synchronized with any heat detection protocol on the Task Force protocol sheet for conventional semen. It is recommended to use sexed semen on females that have exhibited estrus (standing heat) before FTAI and conventional semen on females that have not exhibited estrus (standing heat) at the prescribed time for breeding listed on the FTAI protocol.
The use of estrus detection aids for detecting females in estrus and for best results perform AI 16 to 22 hours after detecting the female in estrus. Synchronization systems used in Bos taurus breeds of cattle do not yield consistently similar results as in Bos indicus-type cattle. The Task Force has listed modified protocols recommended for use in Bos indicus-type cattle. — Dr. Dan Stein, Oklahoma State University Department of Animal and Food Sciences
