Date of Completion

Spring 5-1-2015

Thesis Advisor(s)

Sarah A. Reed

Honors Major

Animal Science


Animal Structures | Biochemistry | Cell Biology | Cells | Cellular and Molecular Physiology | Developmental Biology | Exercise Physiology | Laboratory and Basic Science Research | Musculoskeletal System | Other Animal Sciences | Structural Biology | Zoology


Muscle growth in young horses is characterized by an increase in muscle cross-sectional area, which can be accomplished through the activation and differentiation of satellite cells. Satellite cells can be stimulated or inhibited in response to different cytokines and growth factors and are key mediators of muscle hypertrophy and regeneration. The aim of this study was to investigate the growth of the longissimus dorsi (LD) muscle in horses under 5 years of age and to obtain preliminary data on satellite cell behavior in foals. The area, width, height, and subcutaneous fat were measured using ultrasonography at 6-month increments over the course of 1 year. Area, height, and height to width ratio showed a significant increase by date, but not age, during the second six months and throughout the entire year. Satellite cells biopsied from 5 foals were cultured in the presence of the cytokines interleukin (IL)-6 and tumor necrosis factor (TNF)-α, and the growth factors insulin-like growth factor (IGF)-1 and fibroblast growth factor (FGF)-2. Both IL-6 and TNF-α decreased proliferation of satellite cells. Interleukin-6 increased differentiation and TNF-α decreased differentiation of satellite cells. Satellite cell proliferation was increased in the presence of both IGF-1 and FGF-2, but differentiation was decreased in the presence of FGF-2 and increased in the presence of IGF-1. The results suggest that the LD undergoes hypertrophy over the course of a year in young horses and that satellite cells are influenced by certain cytokines and growth factors that may also affect muscle growth.