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United States Department of Agriculture

Agricultural Research Service

Research Project: IDENTIFY MECHANISMS BY WHICH OVULATORY FOLLICLE SIZE AFFECTS PREGNANCY ESTABLISHMENT AND MAINTENANCE IN BEEF COWS

Location: Livestock and Range Research Laboratory (LARRL)

2009 Annual Report


1a.Objectives (from AD-416)
To improve our understanding of the mechanism(s) by which ovulatory follicle size affects pregnancy establishment and embryonic mortality.


1b.Approach (from AD-416)
ARS – A student from Conapec will visit the Fort Keogh Livestock and Range Research Laboratory (LARRL) and evaluate the effects of serum estradiol and ovulatory follicle size on embryo quality & morphology, and pregnancy establishment & maintenance in beef cows.

Conapec – members will evaluate effects of exogenous estradiol cypionate, equine chorionic gonadotropin, and temporary calf removal on ovulatory follicle size, and establishment / maintenance of pregnancy in large beef herds in Brazil. Information will be mutually shared between involved parties.


3.Progress Report

At Miles City, Montana, individual embryos have been flushed on day 7 following artificial insemination from embryo donor cows that ovulated (released oocytes) from either a large or a small follicles. Embryos were evaluated for morphological development and embryo quality, and all viable embryos that were recovered were transferred within 5 hours of recovery into embryo recipient cows that had ovulated either a large or small follicle. Approximately 80% of the required 360 embryos have been collected, evaluated and transferred. We have evaluated pregnancy in all of these embryo recipient cows to date, but still need to evaluate serum estradiol concentrations in approximately one-half of the cows at the time of breeding in order to characterize the role of estradiol on pregnancy establishment and maintenance. This summer, we will complete the embryo transfers and work on completing hormone analyses of blood samples.

At Brazil, Conapec members have evaluated the importance of exogenous estradiol, equine chorionic gonadotropin and temporary calf removal with regards to ovulatory follicle size on pregnancy establishment and maintenance. Treatment of cows with 300 IU of equine chorionic gonadotropin (which causes both follicle growth and maturation in cattle) resulted in more consistent ovulatory follicle size and improved pregnancy rates. Temporary calf removal caused follicle maturation and increased the incidence of cows exhibiting estrus and thus, improved fertility, but did not affect ovulatory follicle size. Treatment with estradiol did not affect ovulatory follicle size or fertility of cattle.

ADODR monitoring activities include technical oversight at Fort Keogh, conference calls, e-mails, and phone calls.


Last Modified: 4/18/2014
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