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Silva Conceição, Rodrigo

University of British Columbia

The administration of gonadotropin-releasing hormone (GnRH) at the time of artificial insemination (AI) has been associated with improvements in the fertility of lactating dairy cows with low estrous expression. However, the mechanism underlying this association remains unclear. This thesis aimed to evaluate the effect of GnRH at the supposed time of AI and intensity of estrous expression, measured by automated activity monitors (AAM), on the release of luteinizing hormone (LH) following GnRH administration in lactating Holstein cows. The secondary objectives were to explore additional associations of GnRH administration considering concentrations of progesterone (P4) and the uterine response to produce prostaglandin metabolite (PGFM) after an estradiol-oxytocin challenge. In Chapter 1, the scientific literature was reviewed to provide information on the importance of elucidating the effect of GnRH administration at the time of artificial insemination in lactating Holstein cows. In Chapter 2, I demonstrated that the administration of GnRH increased LH concentration during the first two hours following treatment, and the duration of estrus was positively associated with LH concentration. The effect of GnRH administration on LH levels was not associated with P4 levels of the previous estrous cycle or 7d post-estrous event. The administration of GnRH tended to increase circulating levels of PGFM following an oxytocin challenge 16 days post-estrus. In Chapter 3, I discuss the limitations of the randomized controlled study and provide recommendations for future research directions. In conclusion, the results presented in this thesis suggest that administration of GnRH at the supposed time of AI increases circulating LH concentration, which could elicit benefits for dairy cows' fertility. Further research is needed to elucidate the association of P4 concentration of the previous cycle on the response to GnRH administration and on the effect of GnRH administration on P4 concentration 7d post-estrus and uterine capacity to produce PGFM.

Text

2024-08-14

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/88934

Applied Animal Biology

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/