Three growing wethers were used to investigate the differences in nitrogen (N) retention, blood plasma metabolite concentration and energy-yielding nutrient supply to muscle and adipose tissue. The wethers were fed one of three diets: timothy hay with concentrate (THD), Italian ryegrass with concentrate (IRD), and rice straw with concentrate (RSD) for 11 days. The experimental diets were adjusted to the animals to provide 100 g of daily gain. The triglyceride (TG) concentration of blood plasma in arterial and portal veins was higher with THD and IRD than with RSD. Conversely, the available amount of TG in tissues was higher with IRD. The daily amount of glucose and non-esterified fatty acids (NEFA) supplied to muscle tissue and adipose tissue was numerically higher with THD than IRD or RSD. Although N retention did not differ among the diets, it was numerically higher with THD than with IRD or RSD. The results suggest that the difference in the amount of glucose and NEFA delivered to muscle tissue may reflect the N retention in response to forage based diets.