[Effective factors for the reduced feed intake of milk cows fed with rations containing urea]

In two experiments with milk cows with permanent rumen fistula it was investigated whether, apart from urea being unpalatable, further physiologic parameters are responsible for the reduced feed intake. In experiment I the cows received 2, 3 resp 4% urea orally with barley coarse meal, or an equivalent amount was given continuously from the beginning of the feeding over a period of three hours through the fistula. When 2, 3 resp. 4% urea were given orally, the consumption went down in the first 30 min to 58, 52 resp. 40%. When urea was given rumenally, no depression of the consumption could be observed. There were distinct relations with the NH3-concentration in the rumen fluid. At 20 to 35 mg per 100 ml there was no resp. a slight depressioon only and at 40 mg a significant depression. When the concentration rose to greater than 50 mg, consumption was stopped. In experiment II the rumenal application of urea began two hours before the feeding. The high NH3-level shortly after the beginning of feeding (58 mg/100 ml) caused a stop in the feed consumption. No relation could be observed between the urea concentration in veinous blood and the feed intake.