Investigation of different levels of RDP in the rations of lactating cows and their effects on MUN, BUN and urinary N excretion

Twenty-one multiparous Holstein cows in the late stages of their lactation period were used in complete randomized<br />design to investigate the effect of rumen degradable protein on milk urea nitrogen (MUN) and some blood metabolites.<br />Experimental periods were 6 weeks in length, with days 1 to 14 used for adjustment and weeks 3 to week 6 used for<br />sampling (urine, blood, and milk). Three concentrations of a rumen-degradable protein (RDP) supplement according to<br />National Research Council recommendations (9.3, 11.4, and 14% of dry matter intake) were treatments. Dietary RDP<br />content altered both total urinary N and urinary N concentration, leading to increased urinary output. Estimations for<br />microbial protein yield were compared with the measured excretion of purine derivative as yeast RNA equivalent, in urine.<br />No significant effect of concentration of RDP supplement was detected on microbial N production. Plasma cholesterol concentration<br />decreased linearity by increasing RDP concentration in diets (P<.05). In this regard, milk urea nitrogen, as<br />well as triglyceride concentration in plasma, was not associated with dietary RDP concentration. To ensure a correct balance<br />between energy and protein available in the rumen and consequently higher N efficiency for late lactation cows, a<br />MUN content of 15.1mg/dl milk is the upper margin. Milk urea N is a simple and noninvasive measurement that can be<br />used to monitor N efficiency in dairy cows.

Abstract licence: CC BY-NC

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