Nitrogen excretion of fattening heifers fed mixed rations with different crude protein concentrations [Untersuchungen an mastfärsen über stickstoff-ausscheidungen bei fütterung von mischrationen mit unterschiedlichen gehalten an rohprotein]
Pfeffer E.,Der Rheinischen Friedrich WilhelmsUniversitat |
Holthausen A.,Der Rheinischen Friedrich WilhelmsUniversitat |
Griese H.,University of Bonn |
Hovenjurgen M.,Der Rheinischen Friedrich WilhelmsUniversitat |
And 3 more authors.
Zuchtungskunde | Year: 2010
32 Simmental heifers of about 250 kg body weight were fed mixed rations containing, on dry matter basis: 60% maize silage, 10% straw and 30% concentrates. The experiment followed a two-factorial design (2 feeding levels x 4 dietary crude protein concentrations) with 4 repetitions per treatment. Animals were given daily either 68 or 81 g dry matter per kg BW0.75. Because the concentrates contained one of four different levels of crude protein, dietary crude protein concentrations were 76, 94, 112 or 130 g per kg dry matter, respectively. Following a period from adaptation of 3 weeks, faeces and urine were collected quantitatively for five days. Total N was analyzed in feeds, faeces and urine. Urea was determined in urine as well and the difference between total N and urea-N is defined as non-urea-N. No significant dietary influences were found on faecal N or non-urea-N. A highly significant influence existed, however, of N intake on renal excretion of urea. When N intake exceeded the sum of faecal N plus urinary non-urea-N by up to 20 g daily, then 2.3 ± 0.13 g N were excreted as urinary urea. With further increase of N intake, 53% of the additional N ingested were excreted as urinary urea and 47% were retained in the body. Calculated efficiencies of utilization of total dietary N for N accretion in the body at growth rates between 400 and 800 g per day were between 17 and 24%, respectively. © Verlag Eugen Ulmer.