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The objectives of this experiment with Hereford (Hf) and Charolais (Ch) bulls offered grass silage-based diets were to determine the effects on performance, carcass traits and meat quality of the proportion of concentrate in the diet, and the inclusion of rapeseed meal (RSM) in the barley-based concentrate. The two concentrate proportions were 200 and 500 g kg-1 dry matter, fed without or with RSM. The Ch bulls tended to achieve higher gain, produced less fat, had a higher percentage of meat from high-priced joints and had a lower degree of marbling in their meat compared to the Hf bulls. Dry matter and energy intakes, growth performance and carcass conformation improved with increasing concentrate level. Intake parameters and conformation improved more with the Ch bulls than with the Hf bulls as a consequence of increased concentrate allowance. RSM had only limited effects on the performance, carcass traits or meat quality.

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The objective of this meta-analysis was to develop empirical equations predicting growth responses of growing cattle to protein intake. Overall, the data set comprised 199 diets in 80 studies. The diets were mainly based on grass silage or grass silage partly or completely replaced by whole-crop silages or straw. The concentrate feeds consisted of cereal grains, fibrous by-products and protein supplements. The analyses were conducted both comprehensively for all studies and also separately for studies in which soybean meal (SBM; n = 71 diets/28 studies), fish meal (FM; 27/12) and rapeseed meal (RSM; 74/35) were used as a protein supplement. Increasing dietary CP concentration increased ( P < 0.01) BW gain (BWG), but the responses were quantitatively small (1.4 g per 1 g/kg dry matter (DM) increase in dietary CP concentration). The BWG responses were not different for bulls v. steers and heifers (1.4 v. 1.3 g per 1 g/kg DM increase in dietary CP concentration) and for dairy v. beef breeds (1.2 v. 1.7 g per 1 g/kg, respectively). The effect of increased CP concentration declined ( P < 0.01) with increasing mean BW of the animals and with improved BWG of the control animals (the lowest CP diet in each study). The BWG responses to protein supplementation were not related to the CP concentration in the control diet. The BWG responses increased ( P < 0.05) with increased ammonia N concentration in silage N and declined marginally ( P > 0.10) with increasing proportion of concentrate in the diet. All protein supplements had a significant effect on BWG, but the effects were greater for RSM ( P < 0.01) and FM ( P < 0.05) than for SBM. Increasing dietary CP concentration improved ( P < 0.01) feed efficiency when expressed as BWG/kg DM intake, but decreased markedly when expressed as BWG/kg CP intake. Assuming CP concentration of 170 g/kg BW marginal efficiency of the utilisation of incremental CP intake was only 0.05. Increasing dietary CP concentration had no effects on carcass weight, dressing proportion or conformation score, but it increased ( P < 0.01) fat score. Owing to limited production responses, higher prices of protein supplements compared with cereal grains and possible increases the N and P emissions, there is generally no benefit from using protein supplementation for growing cattle fed grass silage-based diets, provided that the supply of rumen-degradable protein is not limiting digestion in the rumen.

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The objective of the present experiment was to study the need for the protein supplementation in the diet of growing dairy bulls (initial live weight 272 ± 28.5 kg and final live weight 666 ± 31.2 kg, on average) fed total mixed ration based on moderate digestible grass silage and barley. The experiment comprised 24 Finnish Ayrshire bulls and 8 Holstein-Friesian bulls and included four treatments. The control diet (C) consisted of moderate digestible (653 g digestible organic matter in dry matter (DM) grass silage (450 g kg -1 DM), barley grain (275) and barley fibre (275) without protein supplementation. Three isonitrogenous experimental diets included also extra protein, i.e. (1) rapeseed meal (RSM) (supplementation 530 g DM per animal day -1 ), (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 isonitrogenous diets the crude protein content of concentrate increased from 137 to 150 g kg -1 DM (9%) compared with the C diet. All bulls were fed total mixed ration ad libitum. The energy content of all diets was 11.6 MJ kg -1 DM. The live weight gain of the bulls tended to be higher with the BPWDS diet than with the C diet (C 1214 vs. BPWDS 1301 g d -1 ; p = 0.10), but the treatments had no significant effect on carcass gain, feed conversion or slaughter parameters. Only the BPWDS diet differed significantly from the C diet in DM (C 9.69 vs. BPWDS 10.38 kg DM d -1; p < 0.01) and energy intake ; p < 0.05). The apparent organic matter digestibility (OMD) was 5% higher in the BPWDS diet than in the C diet (p < 0.001), but the RSM and WDS diets did not differ from the C diet in OMD. The results indicate that the supply of protein in dairy bulls is most probably adequate with moderate digestible, well-preserved grass silage and barley-based concentrates when intake of digestible organic matter is high enough to support microbial protein synthesis in the rumen.