The objective of the study was to compare the effect of different diets on growth intensity, carcass composition and proximate analysis and organoleptic properties of longissimus lumborum muscle. A total of 45 fallow bucks were randomly assigned to three different dietary treatments: P (only grazing), J (barley supplementation), and L (barley supplementation and the addition of lysine). The experiment was terminated by slaughter after 166 days on feed at the average age of approximately 17 months. The animals from the group P compared to those from J and L had significantly lower slaughter weight, average live weight gain and dressing percentage. The P animals had the lowest proportion of carcass fat and the highest proportion of bones and tendons. Significant differences were observed in the content of intramuscular fat which was almost twice as high in the meat of J and L groups as in P. On the other hand, no differences among groups were detected in protein and total collagen contents as well as in the proportion of soluble collagen. The sensory profile of the P group significantly differed in grassy flavour and liver flavour compared to the other groups.