[Dynamics of 15N-isobutylidene diurea (IBDU) in sheep. 1. IBDU conversion in the digestive tract]

Four Merino Landrace wethers averaging 47.6 kg body weight were adapted to a semi-synthetic diet containing as the only N-source 60 g of IBDU per day. After the adaptation phase, on the 1 st experimental day the IBDU of the morning feed was given in 15N-labelled form (701 mg 15N-excess). After 2 1/2, 7 1/4, 12 and 24 hours the experimental animals were killed without having been fed again. The comparison of the IBDU-concentrations in the content of the rumen bottom with the residual rumen content did not allow to draw conclusions regarding IBDU-sedimentation at the bottom of the rumen. For the 15N-decline in the rumen content, a relationship was established following y = 76.3 - 2.62 (r = 0.96) (see fig. 2). In the order of killing times the following 15N-IBDU amounts were retrieved (% of intake): I = 15.6%, II = 24.1%, III = 3.3% and IV = 3.6%. 7 1/4 hours after starting the experiment, 40% of the 15N-labelled material were found in the rumen in the form IBDU; after 12 hours it came to 10%. Except for sheep I, 15N-urea was not found but in small amounts. Only sheep I and III revealed IBDU-traces in the abomasum, but in the small intestine of all sheep 2 to 6% of the amount taken in. This fact is explained with the endogenous influx of IBDU from the blood. An additional experimental sheep provided with a ligature at the abomasum entry, revealed that IBDU is absorbed from the rumen and allowed to enter the individual segments of the intestine in small amounts.