The present experiment was conducted to study diet digestibility, feed intake, animal performance and carcass characteristics of growing dairy bulls offered diets based on (1) whole-crop barley, (2) a mixture of whole-crop barley and hairy vetch (Vicia villosa Roth.) or (3) a mixture of whole-crop wheat and hairy vetch relative to moderate digestible grass silage-based diet. The feeding experiment with 24 Finnish Ayrshire and 8 Holstein-Friesian bulls included 4 forage feeding treatments: (1) grass silage (G), (2) whole-crop barley and hairy vetch mixture silage (BHV), (3) whole-crop wheat and hairy vetch mixture silage (WHV) and (4) whole-crop barley silage (B). In all treatments animals were offered silage ad libitum. The amount of concentrate supplementation was 36 g (W0.75)-1 animal-1 day-1 for all treatments. The concentrate ration included rolled barley and rapeseed meal. Differences between the treatments were compared using an a priori test (Dunnetts test) so that comparison of the diets was based on the G diet. The animals were fed the experimental diets from day 240 to finish at day 505 of age. During the experiment the average concentrate proportions of G, BHV, WHV and B diets were 437, 424, 426 and 423 g dry matter (DM) (kg DM)-1, respectively. There were no significant differences in silage DM intake or in the total DM intake (DMI) (kg DM d-1) between treatments. However, DMI kg-1 W0.75 tended to be 3.5% higher (p = 0.09) in the B diet than in the G diet. Due to increasing energy intake, the gain of the bulls was higher with the G diet than with the WHV diet (p < 0.05). BHV and B diets did not differ from the G diet in gain. Treatments had no significant effect on the dressing proportion or carcass conformation. The carcass fat score of WHV bulls was 29% lower (p < 0.05) than that of the G bulls, but BHV and B diets did not differ from the G diet in carcass fatness. The feed conversion rate (DM intake kg-1 carcass gain) of the bulls was better (p < 0.001) and protein conversion (g AAT kg-1 carcass gain) tended to be better (p = 0.07) with the G diet than with the WHV diet. BHV and B diets did not differ from the G diet in any feed conversion parameters. It can be concluded that replacing moderate digestible grass silage with whole-crop wheat and hairy vetch mixture silage decreased the carcass gain of growing dairy bulls due to lower energy intake and poorer feed conversion. Instead, replacing moderate digestible grass silage with whole-crop barley or with whole-crop barley and hairy vetch mixture silage resulted in no differences in the performance or carcass characteristics parameters of growing dairy bulls.;
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