Date of Graduation

5-2024

Document Type

Thesis

Degree Name

Master of Science in Animal Science (MS)

Degree Level

Graduate

Department

Animal Science

Advisor/Mentor

Charles R. Looney

Committee Member

Jeremy Powell

Second Committee Member

Ken Coffey

Keywords

Artificial Insemination; Beef;Cattle; Hormone; Reproduction

Abstract

In this study, 527 beef heifers from three locations across two states were enrolled between November 2020 and May 2021 for experiment 1, divided into three sub-experiments: 1A (n = 85), 1B (n = 383), and 1C (n = 59). These heifers were randomly assigned to one of four treatment groups. Treatments 1 and 2 involved a 6-day CO-Synch + CIDR protocol, including administration of gonadotropin-releasing hormone (GnRH; 100 μg IM; Factrel; Zoetis Animal Health, Parssipany, NJ) and a CIDR insert (EAZI-BREED CIDR; 1.38g P4; Zoetis Animal Health) on Day 0, followed by prostaglandin F2α (PGF2α; 25 mg IM; Lutalyse HighCon; Zoetis Animal Health) on Day 6, with fixed-time artificial insemination (FTAI) occurring 72 h for Treatment 1 and 80 h for Treatment 2 later. Treatments 3 and 4 followed a 7-day CO-Synch + CIDR protocol with similar initial steps but differed in the timing of FTAI, occurring 54 h (Treatment 3) or 62 h (Treatment 4) after PGF2α administration. Each location in the study was evaluated individually to account for environmental differences. The analysis used GLIMMIX procedures of SAS, including hour as the fixed effect and sheath code, sire, and technician as covariables. Significance was declared at P ≤ 0.05 and tendencies at 0.05 < P ≤ 0.10. In experiment 1A, no significant difference was found between treatments 1 and 2 (P = 0.44), while a tendency for higher pregnancy to AI (P/AI) rates was observed in treatment 4 compared to 3 (P = 0.10). Experiment 1B showed no significant differences between treatments 1 and 2 (P = 0.84) or between 3 and 4 (P = 0.63). In 1C, treatment 2 tended to have a higher P/AI rate than treatment 1 (P = 0.07), with no statistical difference between treatments 3 and 4 (P = 0.33). Experiment 2 involved 240 crossbred beef cows from two locations, randomized into the same four treatments. In experiment 2A, among 189 cows, Treatment 1 had a P/AI rate of 63.04% (29/46), significantly higher than Treatment 2 at 40.81% (20/49) (P = 0.03). No statistical difference was observed between treatments 3 (57.44%, 27/47) and 4 (51.06%, 24/47) (P = 0.53). In experiment 2B with 51 cows, Treatment 1 achieved a P/AI rate of 76.9% (10/13) and Treatment 2 had 53.8% (7/13), with no significant difference (P = 0.22). Similarly, Treatment 3 (76.9%, 10/13) and Treatment 4 (75.0%, 9/12) showed no statistical difference (P = 0.87). This study provides insights into the efficacy of different treatment protocols for enhancing pregnancy rates following AI in beef heifers and cows, emphasizing the potential influence of treatment specifics on reproductive success.

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