Beef production in Finland is based mainly on raising dairy bulls born on dairy farms. Because the supply of domestic beef has been decreasing during recent years, there is nowadays a clear discrepancy between the demand for and supply of domestic beef. Consequently, slaughterhouse pricing favours heavy carcasses, and the average carcass weights of animals have clearly increased in Finland. The prices of the concentrate feeds can vary dramatically, so it would be valuable to obtain information on the performance of dairy bulls slaughtered at heavy carcass weights when they are fed different concentrate levels and different concentrate components. The first aim of this thesis was to produce data for evaluating, developing and recommending biologically and economically efficient energy and protein feeding strategies for growing and finishing dairy bulls offered grass silage-based diets and slaughtered at carcass weights above 300 kg. The second aim was to calculate the energy and protein supplies of the dairy bulls fed different grass silage-cereal-based diets and, based on this, to estimate the possible need to revise the current Finnish energy and protein recommendations for growing dairy bulls. The third aim was to demonstrate the P supply of dairy bulls fed grass silage-cereal-based diets with or without protein supplementation in relation to current feeding recommendations for P. The objectives of the first experiment were to determine the effects on animal performance in various growth periods of (1) the proportion of concentrate in the diet, and (2) the inclusion of rapeseed meal (RSM) in the barley-based concentrate in total mixed ration feeding. The three concentrate proportions were 300, 500 and 700 g/kg dry matter (DM), fed without RSM or with RSM. The live weight gain (LWG) and carcass fat score of the bulls increased linearly with increasing concentrate proportion. Rapeseed meal did not affect animal performance. In order to determine the optimum proportion of concentrate supplementation, estimates of carcass efficiency (kg concentrates per kg carcass), silage substituted (kg DM per kg carcass gain) and true price of concentrates relative to that of forages are required. The objective of the second experiment was to study the effects of partial replacement of barley grain with barley fibre (BF) on animal performance of dairy bulls. There were four diets with two offered at stage 1 (from initiation of the study to 450 kg live weight) and four at stage 2 (from 450 kg live weight to slaughter). The control diet (BF0) included grass silage (460 g/kg DM) and barley grain (540), the BF25 diet grass silage (460), barley grain (405) and BF (135), the BF50 diet grass silage (460), barley grain (270) and BF (270), and the BF75 diet grass silage (460), barley grain (135) and BF (405). At stage 1 there were only two treatments (BF0 and BF50); all four treatments were included at stage 2. The experiment indicated that 50% of barley grain can be replaced with BF without affecting growth, but feed efficiency factors may decrease when barley grain is replaced with BF. The rationality of the use of BF in the future will depend on its price in relation to other concentrates. The objective of the third experiment was to study the need for protein supplementation in the diet of growing dairy bulls fed total mixed ration based on grass silage and barley. The control diet (C) consisted of moderate digestible (653 g digestible organic matter in DM) grass silage (450 g/kg DM), barley grain (275) and barley fibre (275) without protein supplementation. Three isonitrogenous experimental diets included also additional protein, i.e. (1) rapeseed meal (RSM) (supplementation 530 g DM/head/day), (2) wet distillers solubles (WDS) (600 g) and (3) a mixture of barley protein (90 % of fresh weight) and wet distillers solubles (10) (BPWDS) (480 g). In all the isonitrogenous diets the crude protein content of the concentrate increased from 137 to 150 g/kg DM (9%) compared with the C diet. Protein supplementation did not affect significantly animal performance. The results indicate that the supply of protein in dairy bulls is most probably adequate with moderate digestible, well-preserved grass silage and barleybased concentrates when the intake of digestible organic matter is high enough to support sufficient microbial protein synthesis in the rumen. The objectives of the fourth experiment were to determine the effects on animal performance in various growth periods of (1) cereal type (barley versus oats) in the diet and (2) the inclusion of RSM in the grass silage-based diet in separate feeding. The three cereal feeding treatments used were rolled barley, rolled barley + rolled oats (1:1 on DM basis) and rolled oats, fed either without RSM or with RSM. As a consequence of decreased energy intake, the LWG and feed conversion of growing bulls decreased with increasing oats proportion in the diet. Rapeseed meal did not affect animal performance. During the feeding experiments the calculated supply of energy was 10% higher than in the Finnish feeding recommendations for the present growth rate. This indicates that there is a need to update the Finnish feeding recommendations for dairy-breed growing bulls, and further calculations are needed for the energy supply of growing dairy bulls. The calculated supply of AAT (amino acids absorbed from the small intestine) was 38% higher than in the Finnish feeding recommendations for the present growth. Possibly, the present AAT-PBV system is not an optimal protein evaluation system for growing dairy bulls more than 250 kg live weight. The calculations based on the feeding experiments and the Finnish feeding recommendations indicate that in most cases the dairy bulls (live weight more than 250 kg) received enough P from the basic grass silage cereal-based diets without additional mineral feeds. Therefore there is no need to add P in the form of mineral mixtures. Also feeding additional protein increases the P excretion to the environment, because the P content of protein supplements is generally high relative to grass silage and cereals.