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Document Type

Thesis - University Access Only

Award Date

2017

Degree Name

Master of Science (MS)

Department / School

Animal Science

First Advisor

George Perry

Abstract

Proper management of replacement heifers from post-weaning to pre-breeding, to a large extent influences the time when puberty, pregnancy and parturition will occur. Furthermore, in order for a heifer to achieve maximum lifetime productivity she should calve by 24 mo of age (Patterson et al., 1992), therefore, reproductive success becomes essential. Heifers that give birth early in their first calving season remain in the herd longer (Lesmeister et al., 1973; Cushman et al., 2013). In order for a female to pay for her development costs she needs to wean 3 to 5 calves (Clark et al., 2005). Therefore, a reproductively efficient female becomes important to the profitability of any operation. Post-weaning development has historically focused on feeding cereal grains to allow heifers to enter the production system earlier. However, overfeeding heifers has decreased number of calves weaned and increased dystocia (Pinney et al., 1961). Therefore, a Stair-Step compensatory growth program, where females were restricted in caloric intake from 8 mo to 11 mo and then re-fed from 11 mo to 14 mo saw no detrimental effect on fertility (Chapter 3). Heifers on this Stair-Step diet saw an increase in primordial follicles at 14 mo of age. Additionally, mechanisms of primordial follicle action are poorly understood, therefore, serum leptin concentrations, roundabout axon guidance receptor, homolog 4 (ROBO4) and anti-Müllerian hormone (AMH) mRNA abundance were investigated. Leptin was not associated with follicle formation, however, ROBO4 and AMH may be important regulators controlling the number of follicles in the ovary (Chapter 3). Management and feeding strategies are important to reproductive success of beef heifers. Excess dietary protein in diets has been associated with elevated plasma urea nitrogen concentrations (PUN) and decreased fertility through an increase in uterine ion concentrations (pH) in cattle (Jordan and Swanson, 1979; Kiam et al., 1983; and Canfield et al., 1990). We examined the effect of elevated systemic concentrations of blood urea nitrogen on the uterine environment as well as pregnancy success (Chapter 4). Heifers fed a High Protein diet had elevated PUN’s, however, there were no deleterious effects on uterine pH or pregnancy success. Post-weaning to pre-breeding development is important to the reproductive success of a female. These are some development strategies we can address through calving distribution data. However, management of calving distributions could see improvement within the Great Plains. Therefore, to provide insight into the importance of a defined calving season, calving data was gathered from across the state of Nebraska (Chapter 5). Fifteen herds out of 28 (53%) manage an average calving day > 21 d and only 6 herds (21.4%) had heifers calving prior to the cowherd. Our results demonstrate that calving distribution management has room for improvement through different reproductive management strategies and record keeping. In summary, different nutritional strategies during post-weaning and prebreeding are important to the lifetime productivity of replacement heifers. By correctly managing replacement heifers during this time to conceive early can be beneficial to the lifetime productivity and stayability of that female. A female who calves early in the calving season will calve earlier for the remainder of her life and produce more pounds of weaned calf in her lifetime. Therefore, understanding nutritional strategies as well as a calving distribution can help manage a reproductively sound female.

Library of Congress Subject Headings

Heifers -- Feeding and feeds Heifers -- Fertility Heifers -- Reproduction Proteins in animal nutrition

Description

Includes bibliographical references (pages 101-135)

Format

application/pdf

Number of Pages

148

Publisher

South Dakota State University

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Rights Statement

In Copyright