Estrus Synchronization in the Bovine in Response to Limited Administrations of Gonadal Hormones

Effective estrus synchronization in the bovine should have a great effect upon the cattle industry. Successful synchronization of estrous cycles would enable the livestock producer to control breeding and calving dates and give him greater diversity of labor use. The use of artificial insemination would also be greatly enhanced allowing for the use of high quality sires and aiding in the control of certain reproductive diseases. Embryo transfer from animal to animal would also be made easier. The most effective methods of synchronization developed to date have involved either daily feeding or daily injection of hormones. These approaches have limitations under range conditions. It is difficult to get uniform consumption of supplemental feed on pasture. Thus animals must be confined to drylot conditions for the duration of the feeding period to insure consumption of the proper amount of the supplement containing the hormone materials. These problems point to the need for an improved method of estrus synchronization. This experiment was conducted from June to September, 1965, at the Fort Robinson Beef Cattle Research Station, Crawford, Nebraska. The experiment was conducted in a series of 4 trials following a preliminary investigation. Heifers used in these trials were of two general types. One was a group of two-year-old Hereford heifers weighing approximately 800 pounds which were receiving a full feed of ground grain plus a small amount of alfalfa hay. The other group consisted of yearling Angus, Hereford, and Hereford-Angus crossbred heifers averaging approximately 600 pounds. These heifers were on wheat grass pasture until they were assigned to the experiment. They were then shifted to drylot and given 5 pounds of grain and 8 pounds alfalfa hay daily. The effectiveness of limited applications of the gonadal hormones on the synchronization of estrus was studied in 80 yearling and 18 two-year-old heifers. The treatment consisted of a single injection of varying dosages of 16α, 17α dihydroxy-progesterone given concurrently with an injection of 5 mg. estradiol valerate. Advisors: J. N. Wiltbank and D. R. Zimmerma