Incorporation of endogenous urea nitrogen into the amino acids of bacterial protein in the rumen of goats fed diets with various protein levels

Incorporation of endogenous urea nitrogen into amino acids of milk in goats fed diets with various protein levels

“…The high enrichment with 15 N of glutamic acid, arginine, methionine, isoleucine, and lysine can be explained by the high incorporation of EUN in these amino acids of bacterial protein (Michalski et al, 2013).…”

“…The milk protein was hydrolysed in culture tubes, using 6 M HCl in water at 105ºC for 22 h, and the samples were dried with a rotary evaporator at 60ºC. Free amino acids were derivatized according to the procedure specified by Gehrke (2005) that was described in detail in a previous publication (Michalski et al, 2013). N-trifluoroacetyl n-butyl esters of amino acids were analysed using a gas chromatograph with a mass-selective detector using a capillary column (30 m × 0.25 mm × 0.25 µm).…”

“…Water was freely available. Concentrate composition was reported in detail in our previous paper (Michalski et al, 2013). The nutrient contents are given in Table 1.…”

“…From the second day of sample collection, for 6 days goats were administered 15 N-labelled urea (98 atom % excess; VEB Berlin-Chemie, Germany); 1.6 g · d -1 15 N-urea were continuously infused into the jugular vein as described in detail in a previous paper (Michalski et al, 2013). The amount of administered 15 N-urea was chosen based on our previous studies (Michalski et al, 2012).…”

“…It is utilized by rumen bacteria as an important source of nitrogen for bacterial protein synthesis (Virtanen, 1964). This EUN is incorporated in various proportions into different amino acids of bacterial protein; the proportions depend on the composition of the diet (Havassy et al, 1982;Michalski et al, 2013). These amino acids can then be incorporated into milk protein.…”