Animal Science Department


Date of this Version



Published for the Proceedings, The Range Beef Cow Symposium XIX December 6, 7 and 8, 2005, Rapid City, South Dakota.


Reproductive failure is a major source of economic loss in the beef industry. The majority of this loss occurs because cows do not become pregnant during a defined breeding season. Therefore, the goal of any breeding program is to maximize the number of females that become pregnant. This means that fertility plays a major role in the success of any breeding program. There are several methods by which fertility can be measured: 1) conception rates (number of animals pregnant/number of animals inseminated), 2) pregnancy rates (number of animals pregnant/number of animals available for breeding), and 3) calving rates (number of animals calved/number of animals available for breeding). This review will focus on the factors that affect pregnancy rates during the breeding season in both natural service and artificial breeding programs.

Artificial insemination provides a method to inseminate a large number of females to a single sire that has been selected/proven to be an industry leader for economically relevant traits. Thus, genetic change in a herd can occur quickly through the use of artificial insemination. With natural service, herd bulls are also selected for economically relevant traits but are limited on the number of cows/heifers they can service during the breeding season. During the breeding season, a herd bull’s job is to detect cows/heifers in standing estrus and breed them at the appropriate time. For successful artificial insemination of cattle to occur, the producer (herd manager) must take the place of the herd bull in detecting the cows/heifers that are ready to be inseminated. Since pregnancy rates are a product of both estrous detection rates and conception rates, comparisons must be made between synchronized and non-synchronized cows bred by natural service or by artificial insemination.