Using Milk Urea Nitrogen to Predict Nitrogen Excretion and Utilization Efficiency in Lactating Dairy Cows

Abstract

Because animal agriculture has been identified as a major source of nonpoint N pollution, ways to reduce the excretion of N by production animals must be examined. The objective of this research was to develop and evaluate a mathematical model that integrates milk urea N to predict excretion, intake, and utilization efficiency of N in lactating dairy cows. Three separate digestibility and N balance studies (10 diets, 40 cows, and 70 observations) were used to develop the model, and 19 independent studies (93 diets) were used for evaluation. The driving variables for the model were milk urea N (milligrams per deciliter), milk production (kilograms per day), milk protein (percentage), and dietary crude protein (percentage). For the developmental data set, the model accurately predicted N excretion and efficiency with no significant mean or linear bias for most predictions. Residual analysis revealed that a majority of the unexplained model error was associated with variation among cows. For the independent data set, model prediction error was approximately 15% of mean predictions. A mean of at least 10 cows was determined to be appropriate for model predictions. Target milk urea N concentrations were determined from expected urinary N excretion for cows that were fed according to National Research Council recommendations. Target values calculated in this manner were 10 to 16 mg/dl, depending on milk production. Milk urea N is a simple and noninvasive measurement that can be used to monitor N excretion from lactating dairy cows.

Genetic relationship between milk urea nitrogen and reproductive performance in Holstein dairy cows

“…Wood et al (2003) reported similar trends in MUN with stage of lactation. Jonker et al (1998) found a decrease of MUN with advancing DIM from around the second month onward, leading to a curve for MUN similar to that for milk yield. Jorritsma et al (2003) hypothesized that MUN might be increased under a negative energy balance, suggesting a peak in MUN during early lactation like Jonker et al (1998).…”

“…Jonker et al (1998) found a decrease of MUN with advancing DIM from around the second month onward, leading to a curve for MUN similar to that for milk yield. Jorritsma et al (2003) hypothesized that MUN might be increased under a negative energy balance, suggesting a peak in MUN during early lactation like Jonker et al (1998). Broderick and Clayton (1997) also found a positive relationship between MUN and DIM, but the data analyzed by Spicer et al (2000) indicated that MUN increased during the first 3 weeks of lactation, then remained steady for the remainder of the lactation.…”

Performance and metabolite profile of dairy cows fed tropical grasses and concentrates containing crude protein with low or high degradability

“…The concentration of rumen ammonia is an indicator of protein degradation, dietary nitrogen utilization, and microbial growth Russell, 2002). Similarly, the blood urea concentration is a sensitive and immediate indicator of the animal protein metabolism, whereas the milk urea-N is a better indicator than blood urea for evaluating the metabolism of N compounds in the rumen because homeostatic mechanisms do not regulate milk urea-N, a variable less affected by postprandial variations (Jonker et al, 1998). Considering the amino acid requirement of lactating animals and dietary amino acid supply, it is possible that RUP sources can promote better productive responses when combined with forages such as sugarcane or elephant grass silage.…”

Poster Presentations

“…Introduction Milk urea nitrogen (MUN; mg N/dL) is positively related to excretion of urinary urea N (UUN; g/d) (Burgos et al, 2007) and total N (UN; g/d) (Jonker et al, 1998;Bannink and Hindle, 2003) and can therefore be used as an indicator of N-utilization. However, Bannink and Hindle (2003) observed in a meta-analysis on 9 studies that the prediction of UN was substantially improved (R 2 increased from 0.79 to 0.84) when one study, in which the effect of salt intake on urine production was tested, was omitted.…”