Validation of models for predicting milk urea nitrogen concentrations, estimating dry matter intake by the NRC (2001)

Abstract

-The objective of this study was to validate three different models for predicting milk urea nitrogen using field conditions, attempting to evaluate the nutritional adequacy diets for dairy cows and prediction of nitrogen excreted to the environment. Observations (4,749) from 855 cows were used. Milk yield, body weight (BW), days in milk and parity were recorded on the milk sampling days. Milk was sampled monthly, for analysis of milk urea nitrogen (MUN), fat, protein, lactose and total solids concentration and somatic cells count. Individual dry matter intake was estimated using the NRC (2001). The three models studied were derived from a first one to predict urinary nitrogen (UN). Model 1 was MUN = UN/12.54, model 2 was MUN = UN/17.6 and model 3 was MUN = UN/(0.0259 × BW), adjusted by body weight effect. To evaluate models, they were tested for accuracy, precision and robustness. Despite being more accurate (mean bias = 0.94 mg/dL), model 2 was less precise (residual error = 4.50 mg/dL) than model 3 (mean bias = 1.41 and residual error = 4.11 mg/dL), while model 1 was the least accurate (mean bias = 6.94 mg/dL) and the least precise (residual error = 5.40 mg/dL). They were not robust, because they were influenced by almost all the variables studied. The three models for predicting milk urea nitrogen were different with respect to accuracy, precision and robustness.

Variación del nitrógeno ureico en leche según la temporada del año y días en leche

“…Las muestras fueron recolectadas previo al inicio del ordeño y posterior a la limpieza de los pezones, la cual fue realizada con solución yodada al 10% (20), que se recolectaron de los cuatro pezones fueron mezcladas. Una muestra se consideró la mezcla de una deyección por cada uno de los pezones en cada uno de los ordeños, es decir, la muestra de la mañana fue almacenada en una nevera a una temperatura de 6ºC para ser mezclada con la muestra de la tarde y luego fueron transportadas a una temperatura de 4ºC hasta su procesamiento (7,19). Dos muestras por mes fueron tomadas durante todo el período de estudio, para un total de 5.376 muestras en total, sin embargo, se excluyeron 475 muestras debido a aumentos en el conteo de células somáticas por encima de 200.000 células/mL, por lo tanto, el número total de muestras incluidas en el estudio fue de 4.901.…”

Investigation of milk urea nitrogen concentration and factors affecting its variation in Greek Holstein herds

“…The relationship between MUN and various milk components (such as fat, protein and lactose content, fat/protein ratio and somatic cell counts) has been investigated in several studies, with controversial results (Broderick and Clayton, 1997;Godden et al, 2001a;Johnson and Young, 2003;Hojman et al, 2004;Doska et al, 2012;Fatehi et al, 2012;Meyer et al, 2012). Moreover, MUN concentration fluctuates during the year, with higher values usually occurring during the warm months (Carlsson et al, 1995;Godden et al, 2001a;Arunvipas et al, 2003;Hojman et al, 2004;Wattiaux et al, 2005;Bastin et al, 2009;Fatehi et al, 2012).…”

Nitrogênio ureico no leite: ferramenta para análise do >i<status>/i< nutricional de rebanhos leiteiros

“…Quando comparado aos outros clusters observamos que apenas o cluster 1 possui uma associação positiva entre NUL e LACT, ou seja, quanto maoir a concetração de LACT maiores os valores encontrados de NUL, diferente dos clusters 2 e 3 que também apresentaram associação entre as variáveis, porém, em sentido negativo. O que corrobora com os resultados encontrados porMeyer et al (2012), onde observaram uma associação negativa entre as variáveis, a cada aumento de uma unidade percentual de lactose, ocorreu decréscimo na concentração de NUL de, aproximadamente, 1,0 mg/dL.…”