Identifier

etd-08252004-155118

Degree

Doctor of Philosophy (PhD)

Department

Animal Science (Animal, Dairy, and Poultry Sciences)

Document Type

Dissertation

Abstract

There has been great controversy involving progesterone (P4) levels during early pregnancy in cattle. The objectives of these experiments were to determine the effect of an early low dose administration of P4 or altrenogest (ALT) on pregnancy rates in repeat breeder (RPB) females, if an increase in pregnancy rates could result from a direct effect of P4 on the embryo and if ALT could support pregnancy in the absence of a functional CL. Firstly, ALT was evaluated for use as a progestin in cattle by synchronizing estrus in beef heifers. There were no differences in the number of females displaying behavioral estrus or in pregnancy rates when synchronized with ALT or MGA. A second experiment was designed to determine the effect of P4 or ALT supplementation during days 3 to 5 on pregnancy rate in RPB cattle. It was determined that 15 mg of P4 or ALT during days 3 to 5 increased pregnancy rates compared with nontreated breeding periods. A third experiment was designed to determine if P4 exerted a direct effect on the embryo. In vitro produced (IVP) embryos were cultured in the absence of a co-culture system. At day 3, post-insemination, embryos were cultured in the presence of P4 and evaluated on days 6 to 9. On day 7 post-insemination, there were significantly more grade 1 blastocysts from the P4 group compared with other treatment groups. Also, embryo developmental rates were increased when cultured in the presence of P4 and more of these embryos developed to the hatched blastocyst stage compared with other treatment groups. After a direct effect of P4 on developing IVP bovine embryos existed, it was determined that these embryos did not possess P4 receptors. Finally, it was demonstrated that ALT could support pregnancy in the absence of a functional CL. These experiments demonstrated that ALT could serve as a progestin in cattle and when administered in low doses during early pregnancy could improve pregnancy rates in RPB cows. These results are likely due to a direct effect of P4 on the embryo; however, this mechanism is by means other than binding the PR.

Date

2004

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Robert A. Godke

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