Evaluation of Models to Estimate Urinary Nitrogen and Expected Milk Urea Nitrogen

Abstract

Milk urea nitrogen (MUN) has been introduced as a means to estimate urinary nitrogen (N) excretion and protein status of dairy cattle. For Holstein cows, the amount of urinary N excreted (g/d) was originally reported to be 12.54 x MUN (mg/dl), but recently urinary N (g/d) was reported to equal 17.64 x MUN (mg/dl). The objectives of the present study were to evaluate models to predict urinary N and expected MUN, by using older and newer data sets, and to quantify changes that may have occurred in MUN measurements over time. Two data sets were used for model evaluation. Data set 1 was from the spring of 1998 and data set 2 was from the spring of 1999. Similar cows and diets were used in both studies. By using data set 1, the newer model underestimated MUN by an average of 3.8 mg/dl, whereas the older model was accurate. By using data set 2, the older model overestimated MUN by 4.8 mg/ dl, but the newer model was accurate. In the period between the two studies, the MUN measured appeared to decrease by an average of 4.0 mg/dl. By using current wet chemistry methods to analyze for MUN, urinary N (mg/dl) can be predicted as 0.026 x MUN (mg/dl) x body weight (kg). Because of changes in methodology that occurred in the fall of 1998, target MUN concentrations have decreased to 8.5 to 11.5 mg/dl for most dairy herds compared with previous target concentrations of 12 to 16 mg/dl.

Relationship between efficiency of nitrogen utilization and isotopic nitrogen fractionation in dairy cows: contribution of digestion v. metabolism?

“…In recent years, there has been an increased interest in finding biomarkers for the prediction and evaluation of feed efficiency, and in particular ENU (Bertrand et al, 2011;Cheng et al, 2011). Although blood or milk urea-N have classically been used as a predictor of ENU in different species (Kohn et al, 2002), they are not well suited to assessing variations at the individual level (Jonker et al, 1998;Huhtanen et al, 2015) or accounting for variations in the efficiency of use of absorbed amino acids (AA) (Hof et al, 1997). …”

Modeling milk urea of Walloon dairy cows in management perspectives

“…However, target ranges given by the scientific and the practical literature varied. Kohn et al (2002) recommended the 180 to 250 range as target values. Recommendations from the practical literature were more abundant: 215 to 340 (Adam, 2005), 175 to 300 (De Brabander et al, 1999), and 200 to 400 (Deswysen et al, 1997;Juan, 2004).…”

Produção e composição de leite de vacas mestiças suplementadas com diferentes níveis de concentrado mantidas em pastagem de capim Tanzânia irrigada

“…O valor de NUL variou de 14,72 a 16,79 mg/dL (Tabela 6) e está dentro do intervalo, considerado como ótimo, de 8,5 a 16 mg/dL (KOHN et al, 2002). Concentrações ideais de NUL geralmente são atribuídas ao equilíbrio da proteína e dos teores de carboidratos da dieta.…”