The objective was to investigate the influence of crude protein (CP) content in a fattening diet on feed intake, body weight gain, nitrogen excretion, and carcass traits in Holstein steers. Steers (initial body weight 241 ± 26 kg) consumed feed with the following CP content: (a) 17.7% during the early period (from 7 to 10 months of age) and 13.9% during the late period (from 11 to 18 months of age) (HIGH, n  = 3), and (b) 16.2% during the early period and 12.2% during the late period (LOW, n  = 4). The CP intake was lower in the LOW than the HIGH group. Urinary and total nitrogen excretion in the late period tended to be lower (p  < .10) in the LOW than the HIGH group. However, growth performance and carcass traits were not affected by dietary CP content. Free histidine and total amino acid contents in the longissimus thoracis muscle tended to be higher (p  < .10) in the HIGH than the LOW group, however, the CP contents were not affected by dietary CP content. The results of this experiment suggest that decreasing dietary CP to 16% (early period) or 12% (late period) of dry matter would reduce nitrogen excretion from Holstein fattening farms without affecting productivity.

中文翻译：

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日粮粗蛋白含量对荷斯坦奶牛育肥性能和氮排泄的影响。

目的是研究育肥日粮中粗蛋白 (CP) 含量对荷斯坦奶牛采食量、体重增加、氮排泄和胴体性状的影响。阉牛（初始体重 241 ± 26 kg）消耗的饲料中 CP 含量如下：(a) 早期（7 至 10 个月）为 17.7%，晚期（11 至 18 个月）为 13.9%年龄）（高，n  = 3），以及 (b) 早期为 16.2%，晚期为 12.2%（低，n  = 4）。低组的 CP 摄入量低于高组。晚期尿液和总氮排泄量趋于降低（p < .10) 在 LOW 组中比在 HIGH 组中。然而，生长性能和胴体性状不受日粮 CP 含量的影响。HIGH 组胸最长肌中的游离组氨酸和总氨基酸含量往往 比 LOW 组高 ( p < .10)，但是，CP 含量不受日粮 CP 含量的影响。该实验的结果表明，将日粮 CP 降低至干物质的 16%（早期）或 12%（晚期）会减少荷斯坦育肥场的氮排泄，而不影响生产力。