Title page for ETD etd-05112006-161419


Type of Document Master's Thesis
Author Mink, Matthew Ryan
Author's Email Address mmink@vt.edu
URN etd-05112006-161419
Title Evaluation of 72 h Cosynch and 5 or 7 d post-AI gonadotropin releasing hormone on first service pregnancy rate in lactating dairy cows
Degree Master of Science
Department Dairy Science
Advisory Committee
Advisor Name Title
Nebel, Raymond L. Committee Chair
Kasimanickam, Ramanathan Committee Member
Pearson, Ronald E. Committee Member
Keywords
  • post AI
  • gonadotropin releasing hormone
  • synchronization
  • dairy cow
  • conception rate
Date of Defense 2006-05-09
Availability restricted
Abstract
Two studies were conducted to evaluate the effects of 5 or 7 d post-AI GnRH on first service PR, plasma P4, and CL volume in lactating dairy cows synchronized using 72 h Cosynch. All cows were synchronized and randomly assigned to one of three treatment groups: Control – no additional GnRH; 5 d – GnRH 5 d after TAI; 7 d – GnRH 7 d after TAI. In the first study, P4 concentrations were evaluated in samples collected at five separate times and CL volume and number were recorded at 30 d pregnancy examination for Holstein (n = 77) and Jersey (n = 33) cows. GnRH treatment did not affect PR (Control - 47.2%, 5 d GnRH - 40.5%, 7 d GnRH – 44.7%) or P4, but increased TCLV compared to controls (Control – 7.33 cm3, 5 and 7 d GnRH – 10.77 cm3). Incidence of accessory CL increased PR (94.7 vs. 60.6%), P4 (6.95 vs. 5.88 ng/mL), and TCLV (15.51 vs. 6.78 cm3) compared to cows with a spontaneous CL. Cows classified as cycling based on P4 evaluation had significantly higher PR than acyclic cows (54.4 vs. 16.1%). In the second study, Holstein cows (n = 1055) were submitted to the same experimental protocol and evaluated for first service PR. Post-AI GnRH treatment did not significantly affect PR. Primiparous cows (32.8%) tended to have higher PR than multiparous cows (27.6%), but GnRH treatment had no influence on this relationship. In conclusion, GnRH post-AI did not affect PR. Further evaluation of accessory CL incidence is warranted as it significantly affected PR.

(Abbreviations: AI – artificial insemination, CL – corpus luteum, PR – conception rate, P4 – progesterone, TCLV – total corpus luteum volume)

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