An experiment was conducted in the department of Animal Science at the Universidade Federal de Lavras (Federal University of Lavras) for evaluate the effects of protein levels in the nitrogen and energy balance. Twenty crossbred barrows were housed individually metabolism cages and distributed in four treatments. Treatments were isoenergetics and isolisinics diets formulated according ideal ratio of amino acids, but with different crude protein levels (16, 14, 12 and 10%). The pigs were fed three times energy required for maintenance, which was assumed to be 106 kcal of ME/kg of metabolic body weight 0.75. The rations were adjusted each day on the basis of an estimated weight gain. The experiment was conducted in two consecutive periods of 12 days each. Seven first days were used for adaptation of animals and the five last days was used total of feces and urine collection. Ferric oxide was used as a marker. The experimental design was balanced changeover in two periods. The decrease of crude protein levels resulted in linearly reduction (P<0.001) of total nitrogen excretion. For each percent reduction in dietary CP, urine nitrogen excretion was reduced about 10.8%. Nitrogen retention was decreased linearly (P>0.01) for those pigs fed diets with reduced protein. However, nitrogen efficiency utilization of intake nitrogen increased proportionally with decreased crude protein levels. The metabolization coefficients of energy diets showed similarity (P>0.05) values, but metabolizable :digestible energy ratio were inversely proportionally to the crude protein levels. In conclusion, the reduction of crude levels protein of rations decrease nitrogen retention, although result less nitrogen excretion and increase efficiency utilization of nitrogen intake.
Slurry and nutrition; nitrogen balance; pig production
