Date of Award:

8-2019

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Animal, Dairy, and Veterinary Sciences

Committee Chair(s)

S. Clay Isom

Committee

S. Clay Isom

Committee

Allen J. Young

Committee

Irina Polejaeva

Committee

Heloisa Rutigliano

Committee

John R. Stevens

Abstract

Modern high-yielding dairy cows are currently producing far more milk than their ancestors due to a prolonged and intensive genetic selection for milk production trait accompanied by the revolutionary improvement in technology, management, and nutrition. On the other hand, a noticeable decline in fertility and reproductive performance was undeniably consistent with the increase in milk yield. This decline in fertility and reproductive performance are recognized worldwide and well documented in several studies. Dairy cows typically experience a period of energy deficit during the first few months of lactation due to the rapid increase in milk production and limited feed intake. This shortage of energy requirements results in loss of body fat which is associated with the disturbance of the normal levels of certain hormones and metabolites. The significant increase in milk yield has increased the severity and duration of the energy deficit which has an adverse effect on the main reproductive cells and tissues that profoundly contribute to fertility. These include the egg from the ovary, the early embryo, and the internal lining of the uterus. Fertilization of a healthy egg results in the development of an embryo with an excellent quality that can survive through the multiple stages of gestation, especially during the first two weeks of gestation when many embryos die. The embryos in the early stages are the most susceptible to the disturbance in their environment. Energy deficit was shown to negatively impact the egg and embryo quality and make the uterus lining suboptimal to support early embryo development. Understanding the mechanisms by which energy deficit influences the main reproductive tissues will help in developing profound strategies to improve fertility in dairy cows.

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