Landbouwtijdschrift-revue de l agriculture vol:44 issue:5 pages:963-971
In areas with dense populations of animals, the excreta cause major environmental problems. Nitrogen is often excreted in too high amounts. High water contents in animal slurry increase the costs of transport and processing. The objective of the experiments was to evaluate the effects of reduced dietary protein contents on dry matter and nitrogen in the excreta of growing pigs, as well as to study the effect of age on water intake, urine production and nitrogen utilization. Growing pigs, weighing between 20 and 70 kg, were housed in metabolism cages and allowed free access to feed and water. The diet contained 12.9 % of crude protein and was supplemented with l-lysine, dl-methionine, l-threonine and l-tryptophan. The ratio between water and feed intake was 1.43 and was almost constant throughout the experimental period. Urine production, when compared with intake of drinking water, was initially 33 % and increased up to 44 % when the animals reached 70 kg. Nitrogen utilization diminished with age from 62.9 % to 49.2 %. In the second trial three diets containing 18.5 %, 16.3 % and 12.9 % of crude protein were fed ad libitum to fattening pigs (70-85 kg), which were also maintained in metabolism cages. Reduction of the crude protein content from 18.5 % to 12.9 % resulted in a 21 % lower water intake and increased the dry matter content of the excreta (faeces + urine) from 11.7 % to 17.1 %; nitrogen excretion was lowered by 39.2 %. Taking into account that in practical conditions fattening diets contain approximately 16 % of crude protein and that extra water is added to the excreta, it could be calculated that the dietary protein reduction to 12.9 % would eventually result in a relative increase of the dry matter content of the manure by 14.7 %.