INFLUENCE OF NUTRITION ON NITROGEN AND PH OSPHORUS EXCRETION OF LIVESTOCK - MODEL-CALCULATIONS ON THE BASIS OF A LITERATURE-REVIEW

The objective of the present study was to quantify the influence of fe eding on the nitrogen and phosphorus excretion of livestock by means o f model calculations on the basis of published literature data. As the ecological principles on an agricultural farm, where nutrients are mo ving in a cycle between soil - plant - animal - soil, have to be taken into account the excretion was estimated not only per anima but also per unit area. In milk production the excretion of slurry and nitrogen increases with increasing feed intake, milk yield and the content of milk protein. The amount of slurry per unit forage area decreases with increasing forage quality, as the number of cows which can be fed per hectare decreases because of the lower yield under Alpine growing con ditions and the higher forage intake. Depending on milk yield and fora ge quality nitrogen excretions of between 90 and 180 kg N per hectare of forage can be expected. By comparison the amount of N excreted in s pecialized bull fattening systems is up 2.5 times higher because their diet consists of forage maize which has higher yields. The N excretio n per hectare forage maize increases with increasing daily gains. In p ig production there are three possibilities of reducing N excretion as follows: (a) feeding exactly according to their protein requirements (b) optimizing the amino acid composition of the feed protein and (c) by the use of bacterially fermentable cell wall carbohydrates. The amo unt of slurry per unit area depends on the method of production, the y ield of grain and the proportion of purchased feedstuffs and is genera lly between 70 and 180 kg N per hectare. In poultry production, becaus e of the higher proportion of protein concentrates, the excretion of N is about 2.5 times higher. The principals governing the excretion of P are similar to those of N. The amount of P excreted per cow per year increases with increasing milk yield from 8.9 to 10.8 and to 12.7 kg at milk yields of 4000, 6000 and 8000 kg, respectively where P is supp lied according to requirements. Similarly to milk production, P excret ion increases with improved performance due to a higher proportion of purchased feedstuffs also in the case of bull fattening. In addition t o level of supply, anima performance and stocking rate the utilization of P in the different feed sources has a substantia impact on excreti ons. At a P utilization of 50 % and mean daily gains of 700 g the P ex cretions per fattening pig are 750 g. If the P utilization is improved by 10 % the P excretions are reduced by 18.9 %. The results show that nutrient returns to the soil from animal production correspond approx imately to removals by plants under balanced situations of production (fertilization, stocking rate, purchase of concentrates). Increased cr op yields and improved animal performance brought about by purchased f eedstuffs lead to excessive and therefore problematical nutrient retur ns.