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Superovulation of cattle is a technique being used in conjunction with embryo transfer to expedite the propagation of animals with genetic merit for desirable traits. Briefly, these techniques involve the induction of multiple ovulations during one estrous cycle by administering multiple injections of a hormone called follicle stimulating hormone (FSH). Under ideal conditions this treatment will result in multiple embryos. These embryos can then be collected from the cow and transferred to recipient cows of lesser value, which act as surrogate dams. These techniques allow the production of many calves from one cow within a year as opposed to the normal rate of one calf per cow per year.
One major problem often associated with superovulation of cows has been the large variation in the number of ovulations and(or) embryos that result from this treatment. In standard superovulation protocols, injections of FSH are usually initiated during the middle of the estrous cycle (9 to 12 days after estrus). Recent research provides evidence that the large variation in superovulation response may be due in part to the variation in the development of follicles present on the ovaries when treatment with FSH is initiated. Some researchers speculate that the presence of a large follicle on the ovaries of a cow may suppress the ability of FSH to induce the development of other follicles, thereby decreasing the number of follicles that mature and ovulate in response to FSH. One possible approach to overcome this problem would be to begin FSH treatments during the first few days after estrus when the population of follicles on the ovaries is less variable and consists mainly of small follicles. Therefore, it was the objectives of the following experiments to 1) determine an appropriate dosage of FSH to use when superovulating cows during the early stage of the estrous cycle and 2) evaluate whether or not treatment with FSH during the early stage of the estrous cycle (within the first few days after estrus) would result in better superovulation responses that were less variable than standard superovulation protocols that initiate treatment with FSH during the middle of the cycle.