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dos Santos Marques, Jessica Cristina

University of British Columbia

Greater progesterone (P4) levels prior to and post estrus in lactating dairy cows has been associated with improved fertility and greater intensity of estrous expression measured by automated activity monitors (AAM). Recently, greater intensity of estrous expression has also been associated with greater embryo production and quality in superovulated dairy heifers. However, it is unclear whether P4 causes greater expression of estrus and increased early embryo development in superovulated heifers. Therefore, the aim of this thesis was to evaluate the effect of different P4 concentrations in plasma during the follicular growth on the intensity of estrous expression, ovarian response to the superovulatory treatment, and embryo production and quality in superovulated Holstein heifers. In Chapter 1, scientific studies are reviewed to highlight gaps in the literature associated with P4 regulation, intensity of estrous expression and reproductive outcomes in dairy cattle. In Chapter 2, I found that different P4 levels during the follicular growth did not affect the maximum intensity of estrous expression or the duration of estrus in superovulated Holstein heifers. However, high P4 concentrations in plasma during the development of follicles increased embryo quality and reduced the number of embryos produced when compared to low P4 concentrations. Although estrous expression did not relate to the quality of embryos, the duration of estrus and the maximum intensity of estrous expression increased the number of embryos recovered 7 d post artificial insemination. In Chapter 3, study limitations and future directions are summarized. In conclusion, my results suggest that P4 concentrations during the follicular growth, and intensity of estrous expression, are important in regulating the quality of embryos and the number of embryos produced by superovulated heifers.

Text

2022-09-09

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/82681

Applied Animal Biology

University of British Columbia

UBCV

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