chapter  5
14 Pages

Use of GnRH to Synchronize Estrus and/or Ovulation in Beef Cows with or without Timed Insemination

Lactational Anestrus ............................................................................................... 44 Incidence of Anestrus ............................................................................................. 44 Induction of Ovulation ........................................................................................... 46 Uses of GnRH to Synchronize Estrus.................................................................... 48 Uses of GnRH in Timed AI Protocols ................................................................... 50

Ovsynch ...................................................................................................... 50 Cosynch....................................................................................................... 51 Cosynch

+

Progestin................................................................................... 52 Implications............................................................................................................. 53 References............................................................................................................... 54

Traditional estrous-synchronization programs were developed to control the estrous cycle by either inhibiting the occurrence of estrus by providing an exogenous source of progestin (e.g., feeding, drenching, injecting, or implanting) or managing the corpus luteum by administering an exogenous luteolysin (e.g., prostaglandin F

or

PGF

). The challenge faced by the cow-calf producer desiring to use artificial insemination at the beginning of the breeding season is to not only synchronize successfully the estrous cycle but to induce a fertile estrus or ovulation in cows that are yet anestrus when the breeding season begins.