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The aims of the first study were to determine the effects of early weaning followed by a period of high-grain feeding on signaling protein phosphorylation in muscle and on acetate clearance in growing steers.  Twelve Angus X Simmental steers were used in the study.  Six steers were weaned early (EW) and fed a high-gain diet for 148 d and the remainder were weaned at the normal age (NW).  Longissimus muscle tissue biopsies were collected to determine total and phosphorylated forms of AMP kinase and downstream proteins of the mTOR signaling pathway.   Of the 12, 8 steers were used to assess acetate clearance at different age points.  During early grain feeding, phosphorylated:total ratios of rpS6 and S6K1 were greater in EW steers and they had lower acetate clearance rates and greater synthesis rates.   The objectives of second study were to assess the effects of early grain feeding on acetate and glucose turnover rates, palmitate synthesis, and on acetate and glucose preference by subcutaneous, intramuscular and visceral adipose tissues in finishing steers.  Sixteen Angus x Simmental steers were infused continuously with [2H3] acetate (n = 8) or [U-13C6] glucose (n = 8), over a 12 h period immediately prior to harvest.  Plasma acetate and glucose enrichment, and palmitate enrichment in different adipose tissue locations were determined.  There were no treatment effects on acetate or glucose turnover rates or palmitate fractional synthesis rates (FSR).  Acetate turnover and palmitate FSR from acetate were greater than the corresponding rates from glucose.  There were no differences in preference for acetate or glucose among the fat depots. In conclusion, phosphorylation ratios of signaling proteins were not affected treatment.  Acetate clearance increased when steers were heavier and older.  Thus older calves are able to clear more acetate per unit of time and body mass than younger calves reflective of an enhanced ability to utilize the substrate.  There were no differences in preference for acetate and glucose among the major fat depots.  Thus diets leading to high glucose supply will not preferentially direct energy storage to intramuscular stores. / Ph. D.