Factors That Influence Fertility in Synchronized Breeding Programs: Ai or Natural Service

Introduction Artificial insemination provides a method to inseminate a large number of females to a single sire selected and 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 ready to be inseminated. Synchronizing estrus is an effective way to minimize the time and labor required to detect standing estrus in cattle that are going to be artificially inseminated. Furthermore, estrous synchronization can also benefit overall herd management. Cows that respond and conceive to a synchronized estrus have the following advantages: 1) exhibit standing estrus at a predicted time, 2) conceive earlier in the breeding season, 3) calve earlier in the calving season, and 4) wean calves that are older and heavier at weaning. In addition, some estrous synchronization protocols (progestin-based protocols) can induce a proportion of anestrous cows to begin estrous cycles. This will decrease the anestrous postpartum interval and allow for more chances for cows to conceive during a defined breeding season. A study conducted at Colorado State University indicated cows that conceived to a synchronized estrus calved on average 13 days earlier and weaned calves 41 pounds heavier than cows not synchronized (Schafer et al., 1990). 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 (AI or natural service; synchronized or not) 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. This review will focus on the factors that affect pregnancy rates in both natural service and AI and synchronized and non-synchronized breeding programs. Fertility is influenced by many factors, but one of the best methods to look at factors that influence fertility is with the " Equation of Reproduction ". The equation looks at …