Document Type
Honors Thesis
Date of Award
Spring 2024
Abstract
Melengestrol Acetate (MGA) is used to suppress estrus in cattle and is used to synchronize estrus. However, when fed to beef cattle during the absence of a corpus luteum, a transient progesterone producing organ after ovulation, the dominant follicle is unable to regress becoming persistent resulting in decreased fertility of the oocyte. In this study, two treatment protocols were designed to test if administering GnRH, a hormone used to induce ovulation resulting in the formation of a corpus luteum at the beginning of the MGA feeding will prevent fewer persistent follicles and improve the fertility of the ovulation immediately following MGA removal. Heifers were randomly assigned to 1 of 2 treatment protocols, MGA administered for 7 days (7d-MGA) or 14 days (14d-MGA). On day 0 for both treatment groups, all of the heifers were administered GnRH intramuscularly to induce ovulation. Transrectal ultrasound was performed on all heifers using Sonosite Edge Portable Sonogram Machine to assess ovarian status and follicular development and dynamics. Presence of a corpus luteum and characteristics such as follicle size(s) and numbers were recorded. Heifers were then fed to receive 0.5 mg/head/day orally. On day 7, heifers assigned to the 7d-MGA treatment group were administered PGF2alpha to lyse any potential corpus luteum and received Estrotect heat patches to aid estrus detection before being relocated to a separate pasture where they were exposed to fertile bulls for natural breeding. This was repeated on day 14 to all heifers assigned to the 14d-MGA treatment group. On day 71, both the 7d-MGA and 14d-MGA treatment groups were palpated to confirm pregnancy diagnosis. This experiment was done twice with 32 heifers in the first repetition and 14 in the second. The first repetition took place in the summer (June & August 2022), with the second taking place in the winter (January & March 2023). No pregnancy difference (p = 0.67) was observed between 7d-MGA (14/23; 61%) and 14d-MGA (12/22; 55%). A successful protocol designed from this research study could be beneficial in creating optimal breeding efficiency by implementing tighter calving windows and reducing labor/costs when utilized by beef cattle producers.
Advisor
Douglas Eborn
Recommended Citation
Olavarria, Anisa, "Improving Fertility While Synchronizing Estrus in Beef Heifers When Feeding MGA" (2024). Honors Theses. 229.
https://digitalcommons.tamuc.edu/honorstheses/229