Dustin T. Yates
Jessica L. Petersen
Date of this Version
Muscle growth is an important consideration in livestock production that affects producer profits. Producers can maximize muscle growth in animals by decreasing stress and using supplements that increase growth and efficiency. In these studies, we sought to show how stress and growth-stimulating factors affect muscle metabolism in sheep and myoblast function in cattle. First, lambs were fed diets containing no supplement, ractopamine HCl (β1 agonist), or zilpaterol HCl (β2 agonist) for 21 d and housed under thermoneutral or heat stress (40°C, 35% RH) conditions (2x3 factorial). At harvest, skeletal muscle strips were used to measure ex vivo glucose oxidation under basal and insulin-stimulated conditions. Surprisingly, we did not observe interactions among environmental treatment, dietary supplement, and incubation media for glucose oxidation rates. However, heat stress decreased (P ≤ 0.05) muscle glucose oxidation by ~21%, supplementation of β2 agonist increased (P ≤ 0.05) muscle glucose oxidation by ~15%, and addition of insulin to media increased (P 0.05) glucose oxidation by ~25%. Interestingly, supplementation of β1 agonist had no effects on muscle glucose oxidation. In our second study, myoblasts were isolated from cattle with high (/ml; High A4) or control (< 20ng/ml) follicular fluid androstenedione concentrations. High A4 cows consistently wean heavier calves and thus we hypothesized that they have increased myoblast function which might be passed on to their calves. Primary myoblasts were assessed for proliferative capacity (2-h EdU pulse) in growth media (20% FBS) containing no additive (basal), TNFα, or testosterone. Percentages of myogenin-positive and desmin-positive myoblasts were determined after 4-d incubation in differentiation media (2% FBS) containing no additive (basal) or TNFα. No interactions between A4 classification and incubation conditions were found for any output. Myoblasts from High A4 cows exhibited ~9% slower (P ≤ 0.05) proliferation rates but ~25% greater (P ≤ 0.05) percentages of myogenin-positive nuclei and ~15% greater (P ≤ 0.05) percentages of desmin-positive nuclei after 4-d differentiation. These data show that physiological conditions responsible for high levels of A4 in follicular fluid may also be directing skeletal myoblasts to prematurely exit the cell cycle and begin precocious differentiation. Together these studies further demonstrate that stress has a negative impact on skeletal muscle growth, but β2 adrenergic agonists improve muscle growth and that altered androstenedione concentrations also impede proper myoblast function effectively limiting muscle growth.
A final study examined how strengths-based groups affected learning in an undergraduate anatomy and physiology laboratory course. This project aimed to determine if these groups would improve grades and to assess student perceptions about learning and group work. Utilizing the CliftonStrengths for Students assessment students were classified into one of four domains based on their top identified strengths: executing, influencing, strategic thinking or relationship building. Balanced groups (n=9) contained one randomly-selected student from each of the four domains. Unbalanced groups(n=13) contained four students from the same domain. At the conclusion of the semester students completed a final practical exam and a survey of their perceptions on learning and their assigned group. Balanced groups scored greater (P<0.05) on the final practical exam and overall lab scores. However, student perceptions did not differ between the groups and was generally negative. Students in the strategic thinking domain scored highest (P<0.05) whereas relationship builders scored lowest (P=0.05) on the final practical exam as well as the overall laboratory grade. These findings indicate that balancing student strengths in lab groups improves learning outcomes and we believe this simple approach could be applied to in-class group work across many STEM disciplines.
Advisors: Dustin T. Yates and Jessica L. Petersen