Milk Urea Nitrogen as a Tool to Monitor the Protein Nutrition of Dairy Cows

Abstract

The relationship between protein nutrition and milk urea N was investigated in three experiments with a total of 125 cows. After 4 wk of pretreatment, cows received 1 of 13 diets with different ratios of protein to energy for 16 wk. Milk was sampled individually for urea analyses during pretreatment and during wk 1, 5, 10, and 15 of treatment. Results were compared with N losses estimated from rumen fermentation and with N losses of metabolic origin. The mean milk urea N concentration was 12.6 mg/100 ml of milk (range, 9.0 to 18.3 mg). For bulk samples especially, the rumen efflux of crude protein intake was the main determinant of the variation in milk urea N (r2 = 0.81; residual SD = 1.1). However, N losses from the rumen explained only about 50% of the variation in the milk urea N content of samples from individual cows. The N losses of metabolic origin, which, in these experiments, were responsible for 47 to 100% of urinary N losses, were not related to milk urea N. Results showed that regular measurement of milk urea N in bulk samples can be used to monitor N losses from rumen fermentation. However, the value does not give an indication of the efficiency with which the absorbed protein is utilized.

The effect of protected methionine on milk yield and its composition in lactating dairy cows fed grass silage-based diets

“…This aspect of feeding protected lysine and methionine was studied by Hurtaud et al (1995) in cows fed maize silage-based rations. Milk urea concentrations, considered to be a means of monitoring the adequacy of protein nutrition of dairy cows (Hof et al, 1997) were not affected significantly by the treatments. However, they tended to increase over the supplemental doses of protected methionine.…”

Características físico-químicas e perfil lipídico do leite de cabras mestiças Moxotó alimentadas com dietas suplementadas com óleo de semente de algodão ou de girassol

“…A uréia presente na circulação sangüínea tem a capacidade de se difundir livremente para o leite. Desse modo, é possível Tabela 2 -Produção e composição do leite de cabra mestiças Moxotó alimentadas com dietas suplementadas com óleo de algodão ou óleo de girassol estimar a concentração de uréia no sangue medindo-se a uréia no leite, uma vez que os teores de uréia são importantes para o monitoramento da nutrição protéica em rebanhos leiteiros (Hof et al, 1997). São escassas as pesquisas sobre a composição do leite com raças nativas no Brasil; entre os trabalhos, pode-se citar o de Laguna et al (1998), que, avaliando a composição físico-química dos grupos genéticos ½ Moxotó × ½ PardoAlpina, ¼ Moxotó × ¾ Pardo-Alpina e ¼ Moxotó × ¼ PardoAlpina × ½ Anglo-Nubiana (threecross) submetidos a um sistema semi-intensivo, verificaram que o rebanho threecross apresentou valores médios superiores em proteína, gordura e extrato seco total, a 1% de significância, variáveis importantes a serem consideradas na elaboração de produtos derivados.…”

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). …”