Animal Science Department

 

Date of this Version

12-2012

Comments

A DISSERTATION Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Doctor of Philosophy, Major: Animal Science, Under the Supervision of Professors Richard N. Funston and Andrea S. Cupp. Lincoln, Nebraska: December, 2012

Copyright (c) 2012 Adam F. Summers

Abstract

Beef cattle longevity is related to reproductive success, which can be influenced by development system and maternal environment. Three experiments were conducted to determine the impact of development system, maternal protein supplementation, and ovarian steroidogenic environment on beef cattle reproduction. Experiment 1 evaluated the effect of heifer development system on heifer performance and reproduction. Heifers developed on corn residue (CR) had reduced BW from prebreeding through pregnancy diagnosis compared with drylot (DL) developed heifers, but there was no difference in reproductive performance. A subset DL and CR heifers were placed in an individual feeding system to determine feed efficiency during late gestation. Drylot heifers tended to have increased final BW and ADG. In Exp. 2, primiparous heifers were individually fed grass hay and received either no supplement (CON), a distillers based supplement (HIGH), or a dried corn gluten feed (LOW) based supplement during late gestation. Weaning calf BW tended to be greater for steers born to HIGH supplemented dams compared with CON. Similarly, carcass characteristics were altered in calves based on maternal nutrition. The objective of Exp. 3 was to identify the effect of ovarian and follicular environment on oocyte molecular phenotype. Ovariectomy was performed on beef cows approximately 36 h after CIDR removal and PGF administration. Cows were classified as high (HGE) or low (LGE) based on granulosa cell efficiency. Cows classified LGE had increased androgen secretion and expression of steroidogenic pathway enzymes in theca cells. Furthermore, mRNA abundance of ZAR1 was reduced in LGE oocytes. In summary, these experiments support the following findings: (1) developing heifers on CR does not reduce reproductive performance or impact late gestation feed efficiency compared with DL-developed heifers; (2) primiparous heifer protein supplementation improved steer calf weaning BW and altered progeny carcass characteristics; (3) Increased androgen production in LGE animals increases steroidogenic enzyme gene expression and/or mRNA stability during oocyte growth and maturation.

Advisors: Richard N. Funston and Andrea S. Cupp

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