Quantitative and qualitative influences of dietary urea on the composition of duodenal digesta in calves

Abstract

SUMMARYThe aim of the present investigation was to determine the effect of adding urea to a diet based on ground maize and dried sugar-beet pulp (2/1) on the composition of duodenal content and diet digestibility in calves.Two bull calves (140 kg) were provided with duodenal fistulae and pair fed the ration alone or with 1·2% urea in a cross-over design. Lucerne hay was also given. The difference in intake of nitrogen between the two diets was 18·4 g/day.The results obtained showed negligible differences between the diets in the amounts of dry matter, organic matter and energy disappearing both before and after the duodenum. Digestibility of nitrogen was greater with the urea-containing diet.Although some of the added urea (25%) was apparently lost from the forestomach, the duodenal digesta contained 13·7 g N/day more with the diet containing urea. Of this a minimum of 6·5 g was in the form of amino acid-N and only 0·4 g as ammonia-N. All the amino acids determined were present in increased amounts but lysine and isoleucine showed smaller relative increases than the other amino acids.From these results and calculations based on measurements of 2,6-diaminopimelic acid it is suggested that the extra protein in the duodenal content derives from both more efficient bacterial protein synthesis in relation to energy expended and decreased degradation of plant protein in the rumen.