Departments of Animal Science, University of Tehran, Aboureihan Campus, Tehran, Iran
Receive Date: 27 September 2010,
Revise Date: 10 October 2010,
Accept Date: 26 October 2010
Nine multiparous lactating cows averaging 171 days in milk were divided according to days in milk and milk production into three 3×3 Latin squares with three 3-week periods to investigate the effect of rumen degradable protein on milk urea nitrogen. Diets were formulated to provide 3 concentrations of dietary rumen degradable protein (9.8, 10.8, and 11.8% of dry matter), while rumen undegradable protein (4.6% of DM) remained constant. Each period was 3 weeks in length, with 2 weeks used for adjustment and one week used for sampling. Rumen degradable protein levels had a low effect on milk yield (P>0.05), but a significant effect on protein percentage and milk urea nitrogen content. There was linear increase in the milk urea nitrogen content of cows fed diets one to three (P<0.01). Milk urea nitrogen is a simple and noninvasive measurement that can be used to monitor nitrogen efficiency in dairy cows. These results indicated that milk urea nitrogen might be used as a parameter to monitor the change in dietary protein levels.
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