The Management of Drug-induced Manipulation of the Estrous Cycle in Normal Cows and Heifers.

PART I PROSTAGLANDIN-INDUCED SYNCHRONIZATION OF ESTRUS IN BEEF CATTLE: Prostaglandin-induced regression of the mature cyclic corpus luteum in cows and heifers triggers a sequence of physiological events that results in a return to estrus in two to five days. There are several breeding management programs based on this premise. These programs range from attempts to synchronize estrus in entire herds with two injections of prostaglandin eleven days apart and breeding artificially, to simply shortening diestrus in responsive cattle with a single injection and bullbreeding. In this paper, several programs are discussed. No single program will be successful in all situations. Programs must be modified to fit each herd and its management. The factors that most commonly lead to program failure include inadequate nutrition, short postpartum interval, and mismanagement of heifers and first-calf heifers. PART II THE SYNCHRONIZATION OF ESTRUS IN EMBRYO TRANSFER RECIPIENTS USING VARIOUS SYNCHRONIZATION COMPOUNDS: Approximately 1800 recipient cows were synchronized for embryo transplants in three separate trials. The response rates, distribution of estrus, cull rates, and pregnancy rates of the synchronization products were compared. The pregnancy rates in prostaglandin-induced estrus in embryo transfer recipients were found to be no different from those in recipients that were used after natural noninduced estrus. The specific prostaglandin analog fenprostalene was tested for efficacy using various combinations of route of administration and antibiotic addition. There were no adverse reactions and neither the addition of oxytetracycline nor the route of administration had any effect on estrus rate, distribution, or pregnancy rates, which were not different from those achieved with the control prostaglandin analog cloprostenol. PART III TIMED BREEDING IN PROSTAGLANDIN-SYNCHRONIZED DAIRY HEIFERS: Five groups of 20 to 40 Holstein heifers were treated with two doses of cloprostenol eleven days apart. The control groups were bred 12 to 16 hours after first seen in standing estrus. Treatment groups were bred at either 64 or 72 hours postinjection (with no detection) or at more than 24 hours postdetection of estrus. Optimum results were achieved when heifers were bred within 16 hours of first observed estrus or 72 hours after the second synchronizing injection with no detection of estrus.