In animal breeding, synchronization has major role to play especially to bring the animals to estrus at a desired time by using exogenous hormones. Over the past years, a number of substances have been introduced to induce estrus in farm animals. Ovulation may be synchronized with progestins and estrogen combination treatment, a 2-dose prostaglandins (PG) regimen, or a GnRH and PG combination. Progesterone may be considered as a drug of choice, because it is easily applied at low cost. Melengestrol Acetate (MGA), Progesterone Release Intra-vaginal Device (PRID) and Controlled Internal Drug Release devices (CIDR) are progestins approved for use in cows. The five systems for fixed-time insemination with GnRH-PG combinations are Ovsynch, Cosynch, Select Synch, Hybrid Synch and Heatsynch. Hybrid Synch has a lower cost and less handling compared with Ovsynch and CO-Synch but more than Select-Synch. The use of Estradiol cypionate within the Ovsynch protocol may offer dairy producers an alternative. In sub Saharan Africa, the educational level of the farmers, the potential of the available resources (cultivated or natural pastures, rain distribution, water availability, ecological environment, etc.) and the cost of the technology  are factors that explain partially why the use of modern reproductive techniques (estrus synchronization and artificial insemination) are not applied on a commercial scale.

Keywords: Bovine, fertility, GnRH, estrus, progestins, prostaglandins.