Cow and herd variation in milk urea nitrogen concentrations in lactating dairy cattle

Abstract

Milk urea nitrogen (MUN) is correlated with N balance, N intake, and dietary N content, and thus is a good indicator of proper feeding management with respect to protein. It is commonly used to monitor feeding programs to achieve environmental goals; however, genetic diversity also exists among cows. It was hypothesized that phenotypic diversity among cows could bias feed management decisions when monitoring tools do not consider genetic diversity associated with MUN. The objective of the work was to evaluate the effect of cow and herd variation on MUN. Data from 2 previously published research trials and a field trial were subjected to multivariate regression analyses using a mixed model. Analyses of the research trial data showed that MUN concentrations could be predicted equally well from diet composition, milk yield, and milk components regardless of whether dry matter intake was included in the regression model. This indicated that cow and herd variation could be accurately estimated from field trial data when feed intake was not known. Milk urea N was correlated with dietary protein and neutral detergent fiber content, milk yield, milk protein content, and days in milk for both data sets. Cow was a highly significant determinant of MUN regardless of the data set used, and herd trended to significance for the field trial data. When all other variables were held constant, a percentage unit change in dietary protein concentration resulted in a 1.1mg/dL change in MUN. Least squares means estimates of MUN concentrations across herds ranged from a low of 13.6 mg/dL to a high of 17.3 mg/dL. If the observed MUN for the high herd were caused solely by high crude protein feeding, then the herd would have to reduce dietary protein to a concentration of 12.8% of dry matter to achieve a MUN concentration of 12 mg/dL, likely resulting in lost milk production. If the observed phenotypic variation is due to genetic differences among cows, genetic choices could result in herds that exceed target values for MUN when adhering to best management practices, which is consistent with the trend for differences in MUN among herds.

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

“…This was the case in our study, as well. However, mean MY in our study was similar (Arunvipas et al, 2003;Nousiainen et al, 2004) or lower (Godden et al, 2001b;Johnson and Young, 2003;Hojman et al, 2004;Aguilar et al, 2012;Fatehi et al, 2012;Doska et al, 2012) than what has been reported in other MUN studies. Other parameters must also be considered.…”

“…Greater variance (22.7-42%) was found by Johnson and Young (2003), Nousiainen et al (2004), Bastin et al (2009), Aguilar et al (2012), Fatehi et al (2012) and Doska et al (2012).…”

“…Some laboratories report milk urea values instead of MUN and, in order to convert urea values to MUN, they must be divided by 2.14, since the urea molecule consists of 46.65% N. Target values for mean MUN concentration range between 8.5 and 11.5 mg/dL for most dairy herds (Kohn et al, 2002). However, Aguilar et al (2012) suggest that common target values should not be used for all farms without taking into account the normal MUN variation among herds.…”

Revisión de los aspectos para la evaluación de la nutrición y alimentación en programas de salud de hato de ganado lechero I: evaluación del hato

“…El contenido de NUL puede verse afectado por muchas otras variables como etapa de lactancia, número de partos y temperatura ambiental (Fatehi & Young 2012), efecto individual de hato y de vaca (Aguilar et al 2012) y genética de los animales (Mucha & Strandberg 2011), por lo que, nuevamente, su empleo en la toma de decisiones e intervenciones debe hacerse tomando las precauciones del caso.…”

Dehydration as a risk factor for calf mortality in northern Australia

“…This may also apply to measuring hydration status in neonatal calves. The mixed model of (Aguilar et al, 2012) demonstrates how milk urea nitrogen (mg/dL) in multiparous Holstein and Holstein-cross-Jersey cows is partly explained by cow milk yield (kg/d) and cow crude protein intake (kg/d), with respective parameter estimates of -0.33 and 20.3. Therefore, in neonatal calves, the negative association between plasma urea concentration and hydration may be partly confounded, if there is a positive association between plasma urea concentration and milk uptake.…”