Off-campus UNL users: To download campus access dissertations, please use the following link to log into our proxy server with your NU ID and password. When you are done browsing please remember to return to this page and log out.

Non-UNL users: Please talk to your librarian about requesting this dissertation through interlibrary loan.

Quantifying Metabolic Flexibility in Cow-Calf Systems

Joslyn K Beard, University of Nebraska - Lincoln


The overarching objective for these experiments were evaluate metabolism and adaptive mechanisms involved with efficiency in a cow-calf production system. Due to the nutrient demand of lactation and growth, young range cows face metabolic challenges that result in decreased productivity and pregnancy rates. In Exp. 1, 2-yr old lactating beef cows were utilized to determine the impact of forage type on heart rate (HR), grazing behavior, reproductive performance, and metabolism. Body weight (BW) and body condition score (BCS) were recorded biweekly. In addition, body composition via bioelectrical impedance analysis and ex-vivo fatty acid mobilization were analyzed. No differences (P = 0.26) were observed due to distance traveled × HR between grazing groups. Cow BW and BCS are greater (P < 0.001) in cows grazing meadow compared to native upland range. Cows grazing meadow pastures had greater (P < 0.01) ex-vivo fatty acid mobilization and increased (P < 0.01) fat free mass compared to native upland range grazing cattle. Acetate area under the curve, serum glucose and serum urea nitrogen were lower (P < 0.05) in cows grazing native upland range pasture; however, no differences (P > 0.10) were observed in hepatic gluconeogenic capacity between the two forage groups. Cow pregnancy rate (P = 0.10) and days to resumption of estrus (P = 0.73) were not different between meadow and range grazing cows. In Exp. 2, range beef heifers were utilized to determine metabolic differences between pubertal and non-pubertal beef heifers using metabolomics. Heifer ADG (P > 0.10), pregnancy rate (P > 0.10), and percent that calved within the first 21 d (P > 0.10) were not different between pubertal and non-pubertal groups within each calving season. The untargeted metabolomics approached identified differences in branched-chain amino acids, lipid metabolism, carbohydrate metabolism, and steroidogenic biosynthesis in pubertal compared to non-pubertal heifers. Thus, metabolomics may help to identify metabolic efficiency in animals at a young age. In further understanding the metabolic impact on reproductive efficiency in grazing cows and replacement females, results from these studies set the foundation of potential markers of efficiency in cow-calf systems. Identifying and understanding how these mechanisms are correlated and long-term implications on female longevity can revolutionize how we select for sustainable and resilient cow herds.

Subject Area

Animal sciences|Agriculture|Systems science|Sustainability|Biochemistry|Range management|Developmental biology

Recommended Citation

Beard, Joslyn K, "Quantifying Metabolic Flexibility in Cow-Calf Systems" (2020). ETD collection for University of Nebraska-Lincoln. AAI28259140.