DISAPPEARANCE OF DRY-MATTER, N AND N-15 FROM N-15-LABELED FEEDSTUFFS MEASURED BY MEANS OF THE NYLON BAG TECHNIQUE

The disappearance rate of dry matter (DM), N and N-15 of N-15-labelled feedstuffs was measured by means of the nylon bag technique in experiments with a cow and sheep. The disappearance rate of DM, N and N-15 after a 24 hours incubation in the rumen of the sheep was as follows: oat grain: 62,1%, 89,3%, 95,4%; oat straw: 40,1%, 21,0%, 75,5 % and in the rumen of a cow: oat grain: 57,8%, 92,6%, 96,4%; oat straw: 43,4%, 57,7%, 78,3%; feeding oat (green oat): 59,3%, 62,8%, 83,5%; maize sprout: 70,9%, 77,3% 86,0%; sugar beet leaves: 94,1%, 92,8%, 94,2% and barly: 91,5%, 90,4% and 96,0% respectively. The underestimation of the nitrogen loss of feedstuffs during the incubation period in the rumen of sheep and cow is very high in the case of feedstuffs with a high crude fibre content. The reason for this result is the inflow of bacterial nitrogen and/or other nitrogen compounds in the nylon bag and a sorption of this exogen nitrogen on the fibrous material of the feedstuffs. A washing procedure of nylon bags after the incubation period with a detergent solution resulted not in a higher nitrogen disappearance rate in the case of the fibre rich feedstuffs. The true nitrogen loss of this feedstuffs is only measureable by means of N-15 labelled feedstuffs. The N-15-loss represent the true N-loss when the labelling of the feedstuffs with N-15 is homogenous.