This study was designed to investigate the effects and possible interactions of varying crude protein (CP) and digestible energy levels (DE) on Nitrogen Retention, (NR), Urinary and blood plasma constituents in pigs reared from 6 to 60 kg liveweight. One hundred and twenty eight Large White x Landrace pigs weighing 9+1.5kg were assigned to sixteen groups of eight pigs, comprising four females and four castrated males in a 4x4 factorial design, the factors were four crude protein levels: (18, 21, 24 and 27%) and four digestible energy levels: (3,000; 3,300: 3,600 and 3,900 kcal/kg) nitrogen retention studies were conducted during the 4 week after the animals were 4 weeks on test diets. There were 6 pigs (3 females and 3 males) in the nitrogen balance trials. Apparent protein digestibility was calculated from the faecal collection. Urinary urea, citrulline and allocation were also determined. Six out of the eight experimental pigs per diet were selected for bleeding and the plasma urea concentrations were determined. There was a significant ( 0.05) Protein x Energy, Energy X Sex and Protein x Energy x Sex interactions. Females retained significantly higher proportions of their nitrogen intake than the castrated males, the lowest nitrogen retention was obtained on the lowest protein and lowest energy combination. The best nitrogen retention in males was obtained on the 21% protein diet with 3,600 kcal DE/kg, while in females; the best was obtained on the diet containing 24% Protein. Total urinary urea concentration was significantly (p 0.01) influenced by both protein and energy levels and significant Protein x Energy interactions also occurred. Dietary protein, expectedly, significantly influenced plasma urea concentrations tending to be lowest on the two intermediate energy levels; 3,300 and 3,600 kcal DE /kg. Nitrogen retention was optimum between 18 and 21% protein levels and castrated males tended to show optimum nitrogen economy on lower protein levels than female pigs. Total urea concentration paralleled nitrogen retention profile. The Kiriyama Index(A/U x IP) may be a precise method to determine protein requirement for pigs in the humid tropical environment. Digestible energy levels of between 3,300 and 3,600 kcal/kg would be adequate for maximum nitrogen economy.
The nitrogen economy of rice-livestock systems in Uruguay
