Polish Merino małe lambs, average initial weight 16 kg, in 3 groups of 10, werefed to 38-40 kg liveweight on diets with 18,7 MJ/kg DM gross energy and 17 (H), 14 (M) and 10 % (L) crude protein. Six małe lambs of about 40 kg body weight, with simple duodenal and ileal cannulae were fed in a Latin sąuare design on diets of similar composition but containing Cr 2 0 3 and pelleted. Average daily gain in groups H, M, and L was 188, 180 and 159 g; intake per kg gain was : of metabolizable energy 53.7; 52.2 and 50.4 MJ, of crude protein 824, 660 and 595 g, respectively. Ammonia N content in duodenal digesta was on diet L less than on diets H and M (P<0.05). Apparent digestibility of total N in the smali intestine was on diets H and M 68.1%, on diet L 65.4%, the difference being significant (P^0.05). Absorption of essential amino acids was greatest of Met and Lys and least of Thr, regardless of diet. Decreasing the content of crude protein in diets for Polish Merino małe lambs to 14%, at 18.7 MJ gross energy per kg DM, did not reduce the amount of amino acids absorbed in the smali intestine and improved protein utilization.

The chemical and amino acid composition of the empty bodies of 4 lambs slaughtered before fattening and of 12 lambs from 3 gropus (4 in each group) fattened for 113 day with a diet containing 17 (H), 14 (M) or 11%(L) crude protein were determined. The amount of nitrogen and individual amino acids apparently absorbed in the smali intestine during fattening was calculated on the basis of data on their passage to the duodenum and digestibility in the smali intestine. No differences were found in empty body composition depending on the protein content of the diet. The mean daily deposition of protein in the empty body was: 29.7,31.4 and 27.3 g in groups H, M and L, respectively. The utilization of protein for deposition into the empty body weihgt rose (P<0.01) from about 18 to 27% when the protein content was decreased from 17 to 11%. The utilization of metabolic energy available for growth (Ki) was best in group M and amounted to 0.41 in comparison with 0.38 and 0.33 in groups H and L, respectively. The lowering of the protein level in the diets improved the efficiency of utilization of amino acids absorbed in the smali intestine for their deposition in the empty body weight. Essential amino acids and semi-essential amino acids were best utilized by lambs from group M. From all of the amino acids, cystine and glycine were utilized best, with cystine being utilized better in groups H and M than in L. Reducing the protein content in group L to about 11 % resulted in decreasing the percentage of essential amino acids in protein deposited in the body, especially in comparison with the group fed diet M.It seems that the most effective utilization of protein takes place at a 14% crude protein content in the diet.

Digesta were collected from 5 pigs of 33 kg live weight fitted with re-entrant cannulas in the duodenum (within 20-30 cm of the pylorus) and terminal ileum. The pigs received a diet of barley, soya bean oilmeal and a vitamin and mineral mixture. The flow rates of digesta, total nitrogen and the individual amino acids were measured at different time after feeding and during two 24 h periods. A marked increase in the flow of digesta, nitrogen and amino acids was seen in the duodenum after feeding. Total flow during 24 h of nitrogen and amino acids except His, Val, Leu, Phe and Met exceeded intake. Output of nitrogen and amino acids from the duodenal cannula was 117 and 108% of intake, respectively. A method to calculate the ratio of endogenous amino acids in digesta based on the amino acid composition of digesta, diet and endogenous secretions was developed. The calculated amounts of endogenous amino acids passing the proximal duodenum and terminal ileum were 32.2 and 21.9 g per 24 h, respectively. The greatest amount of endogenous amino acids passed through the duodenal cannula in the first two hours after feeding (2-3 g/h) and then gradually decreased to 1 g per hour. The results are discussed in relation to other studies on the secretion of endogenous protein and its amino acid composition.