Using Milk Urea Nitrogen to Evaluate Diet Formulation and Environmental Impact on Dairy Farms

Abstract

Reducing nitrogen (N) excretion by dairy cattle is the most effective means to reduce N losses (runoff, volatilization, and leaching) from dairy farms. The objectives of this review are to examine the use of milk urea nitrogen (MUN) to measure N excretion and utilization efficiency in lactating dairy cows and to examine impacts of overfeeding N to dairy cows in the Chesapeake Bay drainage basin. A mathematical model was developed and evaluated with an independent literature data set to integrate MUN and milk composition to predict urinary and fecal excretion, intake, and utilization efficiency for N in lactating dairy cows. This model was subsequently used to develop target MUN concentrations for lactating dairy cattle fed according to National Research Council (NRC) recommendations. Target values calculated in this manner were 8 to 14 mg/dl for a typical lactation and were most sensitive to change in milk production and crude protein intake. Routine use of MUN to monitor dairy cattle diets was introduced to dairy farms (n = 1156) in the Chesapeake Bay watershed. Participating farmers (n = 454) were provided with the results of their MUN analyses and interpretive information monthly for a period of 6 months. The average MUN across all farms in the study increased in the spring, but the increase was 0.52 mg/dl lower for farmers receiving MUN results compared to those who did not participate in the program. This change indicated that participating farmers reduced N feeding compared to nonparticipants. Average efficiency of feed N utilization (N in milk / N in feed x 100) was 24.5% (SD = 4.5). On average, farmers fed 6.6% more N than recommended by the NRC, resulting in a 16% increase in urinary N and a 2.7% increase in fecal N compared to feeding to requirement. N loading to the Chesapeake Bay from overfeeding protein to lactating dairy cattle was estimated to be 7.6 million kg/year. MUN is a useful tool to measure diet adequacy and environmental impact from dairy farms.

Effects of crude protein level in concentrate supplements on animal performance and nitrogen utilization of lactating dairy cows fed fresh-cut perennial grass

“…Regression equations developed in the current study showed that urinary N output is positively related to MUN output and dietary CP content, which can be used as readily available predictors in practice. Positive relations between urine N output and MUN concentration have been found previously and explained by 8119 the small neutral nature of a urea molecule, allowing MUN to equilibrate with BUN via diffusion into and out of the mammary gland (Jonker and Kohn, 2001). Spek et al (2013) also found that urine N outputs' best sole predictors were feed CP content and MUN content.…”

“…Previous work has shown that MUN concentration and urine N output are positively associated with dietary CP level, most likely a result of increased BUN (Jonker and Kohn, 2001;Huhtanen et al, 2015); therefore, MUN has been suggested as a noninvasive indicator for urine N excretion (Jonker and Kohn, 2001). Concentration of MUN is highly related to dietary CP content, and measurement is common practice in the dairy industry.…”

Biological mechanisms related to differences in residual feed intake in dairy cows

“…Measurements of milk urea nitrogen can be utilized as a diagnostic of N excretion and utilization efficiency in lactating dairy cows, and has a negative non-linear correlation with milk protein content (Jonker and Kohn, 2001). Moreover, excretion of excess urea is an energy requiring process, and properly reducing of milk urea nitrogen can increase milk production (Garcia et al, 1997).…”

Valores de la relación grasa/proteína y nitrógeno ureico en leche de vacas lecheras de la zona norte de Alajuela y Heredia, Costa Rica

“…Analizar los componentes de la leche resulta sencillo y, de una manera alternativa, permite evaluar la nutrición y la detección rápida de desbalances en la dieta y desórdenes metabólicos subclínicos (Jonker & Kohn 2001;Eicher 2004).…”