Title: Influence of follicular characteristics at ovulation on early embryo survival Authors
|Smith, M -|
|Macneil, M -|
|Day, M -|
|Bridges, G -|
|Perry, G -|
|Abreau, F -|
|Atkins, J -|
|Pohler, K -|
|Jinks, E -|
Submitted to: Journal of Animal Science
Publication Type: Review Article
Publication Acceptance Date: November 19, 2012
Publication Date: August 1, 2013
Citation: Geary, T.W., Smith, M.F., Macneil, M.D., Day, M.L., Bridges, G.A., Perry, G.A., Abreau, F.M., Atkins, J.A., Pohler, K.G., Jinks, E.M., Madsen, C.A. 2013. Influence of follicular characteristics at ovulation on early embryo survival. Journal of Animal Science. 91:3014-3021. Interpretive Summary: Several steps are involved with reproductive success in animals. One of these steps is growth of an ovarian follicle that produces a fertile egg that can be fertilized and establish a pregnancy. Critical events must occur to optimize development of a fertile egg. This paper includes a review of literature related to reproductive success in beef cattle. When estrous cycles are manipulated in research and ovulation is induced, some of these factors become more important. The length of proestrus, ovulatory follicle growth rate and size are factors that affect the maturation of the follicle and oocyte at induced ovulation. Length of proestrus, ovulatory follicle growth rate and size are three factors that affect the maturation of the egg. The most critical of a mature follicle is its ability to produce estradiol.
Technical Abstract: Reproductive failure in livestock can result from failure to fertilize the oocyte or embryonic loss during gestation. Although fertilization failure occurs, embryonic mortality represents a greater contribution to reproductive failure. Reproductive success varies between species and production goals, but is measured as a binomial trait (pregnancy), derived by the success or failure of multiple biological steps. This review focuses primarily on follicular characteristics affecting oocyte quality, fertilization, and embryonic health that lead to pregnancy establishment in beef cattle. When estrous cycles are manipulated with assisted reproductive technologies and ovulation is induced, length of proestrus (interval from induced luteolysis to induced ovulation), ovulatory follicle growth rate and ovulatory follicle size are factors that affect the maturation of the follicle and oocyte at induced ovulation. The most critical maturational component of the ovulatory follicle is the production of sufficient estradiol to prepare follicular cells for luteinization and progesterone synthesis and prepare the uterus for pregnancy. The exact roles of estradiol in oocyte maturation remain unclear, but cows that have lesser serum concentrations of estradiol have decreased fertilization rates and decreased embryo survival on d 7 after induced ovulation. When length of proestrus is held constant, perhaps the most practical follicular measure of fertility is ovulatory follicle size because it is an easily measured attribute of the follicle that is highly associated with its ability to produce estradiol.