HORMONAL METHODS FOR ESTROUS CYCLE MANIPULATION IN DAIRY COWS

Reproduction efficiency in dairy cows is declining all over the world. Epidemiologic studies suggest that diseases have greater effect on herd fertility compared to the parameters like milk production. Immediate solution to the problem of infertility may be the application of some method of hormonal manipulation of estrous cycle in dairy cows. Reproductive system ultrasound examination enables today’s veterinarians to visualize ovarian changes during the estrous cycle, giving them a chance to intervene with exogenous hormonal inhibition and/or stimulationof temporary ovarian structures at the appropriate time. Summarizing possible hormonal methods for estrous cycle manipulation we have analyzed following protocols: prostaglandin based protocols, prostaglandin + progestagensin combination, regimes using prostaglandin + gonadotropin-releasing hormone (GnRH) and prostaglandin + GnRH+ estradiol protocols. In dairy herds where estrus detection does not represent a significant problem, prostaglandin based or Select Synch protocols are methods of choice for the hormonal manipulation of estrous cycle.
However, if there are problems regarding estrus detection Ovsynch or Presynch + Ovsynch could be an effective alternative for the hormonal manipulation of estrous cycle. Furthermore, fixed time artificial insemination (TAI) could be modified to coincide with the second GnRHinjection, thus reducing the time and number of visits.