John D. Reed

Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)


Animal Science


Artificial insemination (A.I.) has been commercially available to beef producers for nearly 20 years. However, most beef cattlemen do not use A.I. because of the labor and management required during the long breeding season. Successful estrus synchronization would allow optimum use of labor and facilities thus allowing maximum use of A.I. It would also enable the producer to more closely control calving dates. Thereby assuring a more uniform group of offspring at market time. More effective use of A.I. would also enhance the use of outstanding performance tested sires and aid in control of certain reproductive diseases. Control of the female reproductive system would also be useful to the research scientist. Some experimental variables could be removed if all animals were bred on a specific date. Embryo transfer could be simplified if donor and recipient were synchronized. Various hormone treatments have been developed which prohibit manifestations of estrus and ovulation until after withdrawal of the exogenous autacoid. However, reduced fertility at the synchronized estrus has offset any apparent advantages. Fertility at the second estrus post-treatment appears to be normal, but the effects of synchronization are lost due to variation intime of estrus following treatment and differences in length of individual estrous cycles. Since the initial observation that the removal of the corpus luteum would shorten the estrous cycle in guinea pigs, much research has been done to develop an effective method of estrus synchronization. Most of this research has been done with the use of exogenous and endogenous progestins.

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South Dakota State University