The effect of protein supplementation on nitrogen utilization in lactating dairy cows fed grass silage diets.

摘要: The study set out to examine the effects of supplementing grass silage with various levels protein concentration and degradability on dietary nitrogen (N) excretion in lactating dairy cows consuming at least 60% forage. Six Holstein/Friesian early midlactation were offered six diets comprising two crude (210 290 g/kg DM) three concentrate achieved using different amounts untreated or formaldehyde-treated soybean meal. Despite a difference almost 100 g/d N intake, apparent fecal milk outputs not significantly affected. Protein also had no effect feces milk. However, there was major both level CP urinary output. Moreover, an interaction between detected, such that rate which increases increasing higher high-CP than low-CP diet. A low (150 DM diet) medium rumen-degradable supplements provided significant reduction without compromising lactational performance (mean 24.8 kg/d), terms yield composition. This demonstrated high efficiency utilization could be (supplying less 400 g N/d), being main route excretion, whereas exponential observed as intake exceeded N/d.