REDUCING OF NITROGEN EXCRETIONS OF THE LA YING HENS BY FEEDING LOW CRUDE PROTEIN MIXTURES AND APPLYING OF FEED SUPPLEMENTS

The experiment was performed on 240 middle-heavy hybrid layers of Hise x Brown. 17-weeks-old hens were fed with mixture containing 15% crude protein (CP) and 11,3 MJ ME/kg of mixture to the moment of laying-star t. The body weight of hens in begin of experiment was in mean 1,77 kg. The hens were kept in cages (3 birds per cage) in the room without th e air condition. The layers were fed with experimental mixtures contai ned different level of CP: 13,4; 14,5 and 16,1% and the constant energ y concentration amounted by 11,4-11,2 MJ EM/kg. In mixtures were used the vegetable origin feeds only. Vitamins and minerals were added as t he premix DJ. During the experiment (228 days) the following basics pa rameters were controlled: weight gain, laying rate, egg mass, feed int ake and mortality of hens. Three nitrogen balances were performed in t he same cages in 2nd, 4th and 6th months of laying when the laying rat e amounted 92, 82 and 80%. Layers were fed with 120-130 g of mixture p er day and head, the rests of feeds were precisely weighted and its co mposition were estimated. In the successive series to the each of mixt ure Avoparcin (10 ppm), Roxazyme (200 ppm) or Virginiamycin (20 ppm) w ere added. In the lowest concentration of CP in feed (13,4%) the lower about 11%, in 14,5% of CP in mixture lower about 9% of nitrogen excre tion were find out, what do it mean the reducing of weighting of envir onment by nitrogen. Introducing of feed supplements into the mixtures unsignificantly increased nitrogen intake without the largest changing in its excretion. N-utilization was better at 3%, at 3% lower was N-r etention in egg mass. Retention of N in body' tissues was proportional ly in contrast to the N retention in mass of produced eggs. Along with the age of hens increased N intake (from 3,307 up the 3,654 g), N-exc retion (from 1,631 up to 2,546 g per day and head; P < 0,01). Total re tention of nitrogen decreased from 1.676 to 1,108 g. In comparison to intake it was decreased from 51 to 30%, what correspond with the rise of unutilised nitrogen. Older hens excreted in mean about 41% of nitro gen more than younger birds.