[Isobutylidene diurea as an NPN source for ruminants. 1. Rumen fermentation, digestibility of the nutrients and microbial protein synthesis in dairy cows].

In 3 experiments 2 lactating dairy cows received a mixed ration consisting of 10 kg maize silage, 2.5 kg hay, 2.0 kg barley, 1 kg dried sugar-beet pulp, 1.5 kg maize starch, 0.5 kg sugar, 0.2 kg of a mineral-vitamin mixture and 0.08 kg non-protein nitrogen (NPN) per animal and day. The ration contained 8.3 kg dry matter, 5.1 kEFU cattle and 1.18 kg crude protein, 0.5 kg of which from NPN, and was given in equal shares twice a day. Urea (I) or isobutylidene diurea (IBDU), to which the animals were not adapted (II) resp. adapted (III), were the sources of NPN.IBDU proved to a be a very slow source of NH3 in the rumen. 2 hours after the intake of NPN 48 . . . 75, 5 . . . 9 and 5 . . . 12 mg NH3/100 ml could be detected from I to III. Up to the third hour the concentration of IBDU and urea increased in III, which is due to the slow distribution of the slowly soluble IBDU in the fluid digestaphasis. 12 hours after the feeding the level of IBDU and urea in III still amounted to 25 mg urea/100 ml, in I to 1 mg/100 ml only. In the first 3 hours after supplying the NPN the pH-value of I was more than 1 unit higher than that of II and III. There were no significant differences in the fermentation models between the variants, the concentration of volatile fatty acids was 12.6, 12.3 and 11.1 mmol/100 ml. In the stomachs the digestibility of the organic matter was 52, 51 and 54%, that of the crude cellulose 64, 62 and 66% and that of the starch 91, 93 and 98%. At the duodenum the passage rate of N was 87 . . . 93, 107 . . . 126 and 96 . . . 130% of the N-intake, that of NH3-N 6, 43 and 22 g per day and that of bacteria-N 61 . . . 76, 78 . . . 100 and 76 . . . 96% of the N-intake. 2.3 . . . 2.8, 2.6 . . . 3.2 and 2.1 . . . 3.1 g bacteria-N were formed per 100 g dry matter fermented in the rumen. In the intestines 55 . . . 61, 57 . . . 64 and 48 . . . 71% of the feed-N were available as non-NH3-N. The conclusion is that in comparison to urea and concerning IBDU, the rumeno-hepatic circulation plays a definitely bigger role for the N-supply of the rumen microbes and that the possibility of the better N-utilisation can be derived from that.