To estrus dedect or not was the question |

To estrus dedect or not was the question

Summarized by Rick Funston
UNL Beef Reproductive Physiologist

Artificial insemination allows producers to utilize superior genetics for less than purchasing a herd sire of similar quality. Estrus synchronization also can shorten the calving season, increase calf uniformity, and facilitate the use of AI.

Estrus synchronization and AI require planning and additional time and labor, which are the most cited reasons why producers don’t use these reproductive technologies. Fixed-time AI protocols eliminate estrus detection and reduce the number of times cattle are handled. Melengestrol acetate (MGA) is a progestin commonly used to synchronize estrus in beef heifers and has proven to be as effective as controlled internal drug release device in timed AI protocols in beef heifers.

A question remains whether there is opportunity to increase AI conception rates with estrus detection. The objective of the present study was to compare modified estrus detection vs a fixed-timed AI MGA-prostaglandin F2α (PG) synchronization protocol.

Yearling, Angus-based crossbred heifers (n = 972) at the Kelley Ranch near Sutherland, NE, were fed to achieve 60 percent mature BW at breeding. Heifers were either developed in a drylot or a combination of dormant meadow and drylot.

All heifers were synchronized using a MGA-PG protocol (see the Applied Reproductive Strategies in Beef Cattle Resources page). Also at PG injection, estrus detection aids, or patches, were applied. At 72 hours after PG, all heifers in the fixed-timed AI protocol received 2 mL GnRH injection and were AI. Heifers in the modified-time AI treatment were heat checked at 58 and 70 hours after PG. Heifers expressing estrus were sorted off. Approximately 72 hours after PG, heifers were AI in the following order: heifers sorted off at the first heat check, heifers sorted off at the second heat check, and heifers not expressing estrus at either heat check. Heifers not expressing estrus did receive GnRH at AI.

Prior to breeding, heifers weighed 62 percent of mature weight, based on 1,220 lb mature cow. Heifers not heat checked were handled less, requiring less labor and time, and still achieved similar AI conception rates (62 percent) as heifers in the modified heat check/timed AI protocol. Final pregnancy rates were similar as well (96 percent).


Regardless of AI protocol, heifers in heat at AI had higher AI conception rates compared with non-estrus heifers. Reproductive technologies such as estrus synchronization and AI have limited adoption in the beef industry, partially due to added labor. Protocols that limit labor and cattle processing have a greater potential of being adopted. This study provided a synchronization and AI protocol that limits cattle handling and eliminates estrus detection without compromising conception rates.