The effect of the amount of urea in the diet on the contents of amino acids and other components of duodenal digesta in young bulls.

Young bulls of average live weight 130 kg, with rumen cannulae and re-entrant cannulae of the proximal duodenum, were fed on a diet of maize meal from whole plants, potato starch and a mineral mixture, containing 7.6% crude protein in DM (group IV). For three groups the diet was supplemented to contain about 17.5% crude protein with groundnut oilmeal (group I), grundnut oilmeal and urea, 27 and 31.2% of dietary N (group II) or urea alone (group III). The content of gross energy was similar in all diets. The amount of total N entering the duodenum in groups I to IV was 61.6, 59.2, 49.9 and 38.0 g/day and apparent digestibility of N in the stomachs was -0.4, 5.8, 21.6 and -44.4%. Total amount of amino acids in the duodenal digesta was, in the same order, 257, 261, 215 and 170 g/day, equivalent to 80, 116, 165 and 127% of intake. The ratio of the amounts of essential to nonessential amino acids was in feed 0.84 and in duodenal digesta in all groups 0.98. The amount of lysine in duodenal digesta was 1.5, 2.0, 3.5 and 2.5 times its intake in the same order of the groups.

Incorporation of 15N-urea into individual amino acids of rumen bacteria and blood plasma protein in sheep.

Two sheep weighing about 25 kg were fed on rations with similar nitrogen content (about 9 g N/day including 15N from 5 g labelled urea) but with different content of readily digestible carbohydrate. Concentrate ration consisted of maize meal (whole plant) 300 g + barley meal 100 g + mineral mixture 20 g + urea 5 g; fibrous ration--meadow hay 250 g + oat straw 170 g + mineral mixture 20 g + urea 5 g. Retention of 15N was 53.8 and 43.6% of intake in sheep on concentrate or fibrous diet, respectively. Incorporation of 15N into individual amino acids of bacterial protein isolated from the rumen and blood plasma proteins was different, depending on the ratio and amino acid. Enrichment of 15N of the bacterial matter and plasma proteins in both sheep exceeded that of individual amino acids, indicating that urea nitrogen was utilized to a large extent for the synthesis of nitrogen compounds other than amino acids.

Utilization of urea 15N for the synthesis of the rumen microorganisms and blood plasma protein in sheep.

Two sheep were fed a diet containing urea and high level of easy fermentable carbohydrate or crude fibre. Incorporation of urea 15N into the total and bacterial N in rumen and NPN of blood plasma was higher, but lower into plasma protein in the sheep fed the diet with easy fermentable carbohydrate. The analysis of data of the rate of enrichment with 15N in protein and NPN of plasma and rumen liquid suggests that urea nitrogen was fixed transiently into plasma protein and after releasing and recirculation throughout the rumen incorporated permanently into plasma protein.

Passage of the intravenously administered 15N urea into the digestive tract and its excretion in the sheep.

The experiments performed on two wethers provided with simple rumen cannulas and reentrant cannulas, inserted into the proximal duodenum and ileum, showed a passage of 15N from labelled urea, injected intravenously, from the blood to the digestive tract. The amount of the 15N in the digesta was the highest in duodenum, slightly lower in the rumen and slightly lower in ileum. Approximately 50% of the injected 15N was excreted in urine. The amount of the 15N eliminated with feces was very small; 0.6 to 2.8% of the dose injected per day. About 73--84% of the 15N which passed the duodenum was absorbed in further parts of the digestive tract. It can be concluded that all parts of the digestive tract take part in utilization of the endogenous urea.

Incorporation of N from intravenously administered 15N labelled urea into the bacterial protein in the sheep.

The experiment carried out on two wethers demonstrated that nitrogen of intravenously injected urea, labelled with 15N was incorporated into total and bacterial nitrogen fraction of the digesta flowing through the rumen and duodenum. The amount of 15N in the bacterial fraction flowing throught the rumen and duodenum was relatively low in comparison with the amount of 15N in the total nitrogen (14,8% and 8,1% in the rumen and 6,6% and 7,9% in the duodenum. The ratio of the amount of bacterial-N to total-N in the rumen content (12,7 and 7,5%) was only slightly lower than the ratio of bacterial 15N to total 15N. In the duodenum this ratio was a little higher (8,7 and 10,0%). Blood urea nitrogen was utilized only partly in biosynthesis of bacterial protein. The results showed that only a small amount of blood urea nitrogen retained in the organism was utilized for microbial protein synthesis and the majority in some different way.