Date of Graduation

5-2025

Document Type

Thesis

Degree Name

Master of Science in Animal Science (MS)

Degree Level

Graduate

Department

Animal Science

Advisor/Mentor

Looney, Charles R.

Committee Member

Littlejohn, Brittni P.

Second Committee Member

Powell, Jeremy G.

Keywords

Artificial insemination; Beef cows; Fixed-time; Pre-synchronization

Abstract

Adoption of artificial insemination by beef producers has been limited within the United States. Estrous synchronization (ES) for fixed-time artificial insemination (FTAI) has been one of the most effective ways to implement artificial insemination into beef production systems, but its efficiency has primarily been restrained by the dependency on the effectiveness of the initial gonadotropin releasing hormone (GnRH) injection in many FTAI protocols. The hypotheses of these studies were to determine practical methods of pre-synchronization to improve current FTAI protocols, ultimately increasing beef herd reproductive performance. The objective was to evaluate the use of prostaglandin F2α (PGF) and progesterone (P4) to increase the effectiveness of the initial GnRH injection within protocols to increase the synchronization of estrous cycles within a herd, ultimately increasing the number of pregnant animals. Utilizing P4 and PGF as a method of pre-synchronization for a shortened ES protocol induced a greater percentage of animals exhibiting estrus behavior compared to animals that had received only PGF as a method of pre-synchronization or no method of pre-synchronization. Cows subject to methods of pre synchronization also resulted in a greater percentage of animals pregnant to AI than those not receiving a method of pre-synchronization. Furthermore, evaluation of pre-synchronization utilizing P4 and PGF prior to differing FTAI protocols yielded AI pregnancy results that may contrast with the typical relationship of estrus expression and AI pregnancy rates within fixed time artificial insemination protocols. Evidence suggests that the use of P4 and PGF in methods of pre-synchronization within ES protocols provide potential in producing greater reproductive outcomes and provide evidence as a potential method to further improve the efficiency of the beef production industry.

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