REDUCTION OF NITROGEN-EXCRETION IN FATTEN ED PIGS BY UTILIZATION OF SYNTHETIC AMINO-ACIDS

Three metabolism trials with 24 barrows - crossbreds of average weight 40 kg were conducted in order to determine the conditions for a signi ficant reduction of nitrogen excretion at analogical productive effici ency of feed mixtures by means of reduction of dietary protein content and utilization of synthetic amino acids. Experimental feed mixtures were formulated for fattened pigs of the weight 35 to 65 kg while tria l 1 had the higher level of crude protein, trial 2 medium level of cru de protein and trial 3 the lower level of crude protein. Mixtures A2K consisted mostly of grains and proteinaceous feeds in all the trials, in mixtures A2A a part of proteinaceous feeds was compensated by synth etic amino acids and mixtures A2N were identical with relevant mixture s A2A while no synthetic amino acids were used (trial 1 and 2). The fo rmulations of experimental feed mixtures are shown in Tabs. I and II. Nutritive value of feed mixtures is given in Tab. III. With the crude protein content LYS content is decreasing in A2K mixtures, but its per centage out of crude protein is standard (4.72%). In mixtures A2A the LYS percentage is increasing at a decrease in crude protein content (4 .28% in the first trial, 5.54% in the second trial and 6.08% in the th ird trial). The LYS percentage out of crude protein made 39% to 4.0% i n feed mixtures A2N. The relationships between the contents of LYS, TH R and thio amino acids are different, and only in mixtures A2A in tria ls 2 and 3 they approach the cited data (Anonym, 1993; Schulz, 1993; S imecek et al., 1993). All metabolism trials were conducted by Latin-sq uare method, trails 1 and 2 with nine pigs (3 x 3 x 3), trial 3 with e ight pigs (2 x 2 x 4). Balance period lasted nine days, four days were a preparatory period followed by five-day balance period (collection of excrements and urine). Nitrogen balance was investigated (feeds, ex crements, urine). No significant differences in nitrogen digestibility and utilization were determined in trial 1. Nitrogen excretion decrea sed by 6 - 9%, which corresponded to the lower nitrogen uptake only. I n trial 2, in which LYS and crude protein values approached common all owances, utilization of N uptake was significantly better for mixture A2A than for A2K (by 16.5%) while nitrogen excretion decreased by 15.9 %. In trial 3, in which the concentration of crude protein was still d ecreased, utilization of N uptake was higher by 11.1 % for mixture A2A in comparison with A2K, the differences were, at the level of signifi cance. N excretion decreased by 193% if both groups were compared. N e xcretion reduction was significant both in trial 2 and trial 3, as a r esult of lower uptake and better utilization. On the basis of the resu lts the content of 14.7% dietary crude protein and 12.9 MJ ME per kg m ixture are recommended for production of pigs at the weight of 35 to 6 5 kg. We also recommend the content of 0.88% LYS, 0.60% THR and 0.55 M ET + CYS in the feed mixture, which means 6 per cent LYS out of crude protein and LYS: THR: MET ratio 100 : 68 : 62. Under those conditions, N excretion can be decreased by 14 to 16% in comparison with common a llowance while productive efficiency of mixtures is not reduced. These data are recommended for the conventional type of pigs (LW x L x sire of meat breed). Positive economic effect (feed mix price) depends on the price relations of proteinaceous feeds and synthetic amino acids.