Impacts of Age, Genotype and Feeding Low-Protein Diets on the N-Balance Parameters of Fattening Pigs

The effects of feeding low-protein (LP) diets and the age and genotype of fattening pigs were evaluated in an N-balance trial. Sixty weaned piglets of two genotypes were allotted to three different diets. Besides the control diets for the crossbred Topigs 20 × DanBred Duroc (TD) and Hungarian Large White (HLW) pigs, two LP diets were fed containing 1.5 (T1.5) and 3% (T3) less dietary protein than the control. The LP diets were supplemented with crystalline lysine, threonine, tryptophan, and methionine to equalize their digestible amino acid contents. Starter diets were fed between 20–30, grower I between 30–40, grower II between 40–80 and finisher between 80–110 kg live weights. Pigs were kept in floor pens, with 10 animals per pen. In all phases, six pigs with similar live weight were placed into individual balance cages and in the frame of a seven-day long balance trial, the daily N-intake, fecal and urinary N-excretion were measured. From the data N-digestibility, the total ammoniacal nitrogen (TAN) and N-retention were calculated. All the investigated main factors, the genotype and age of pigs and the protein content of the diets had significant effects on the N-balance of fattening pigs. The determinacy of the factors depended on the investigated parameter. Fecal N-excretion and N-digestibility were steadier compared with the urinary N-exertion and TAN percentage. N-digestibility increased and the urinary N-excretion decreased when LP diets were fed. The urinary N-decreasing effect of LP diets was not linear. Compared with the control (19.6 gN/day), T1.5 treatment resulted in 14.5, treatment T3 in 12.4 g daily urinary N-excretion. The TAN and the N-retention of HLW pigs were more favorable than those of TD pigs. Based on our results, it can be concluded that the accuracy of the nitrogen and TAN excretion values of pigs, used in the calculation of the national NH 3 inventories, could be improved if the genotype, the more detailed age categories and the different protein levels of feeds are considered.