Use of digestible rather than total amino acid in diet formulation increases nitrogen retention and reduces nitrogen excretion from pigs

Abstract

One of the goals of swine diet formulation is minimizing nitrogen (N) excretion as well as maximizing N retention. This study was conducted to test the hypothesis that different requirement expressions of dietary amino acids (AA) may affect N balance in pigs. Twelve pigs with average body weight of 40.9kg (standard deviation =3.3) were used in a quadruplicated 3×3 Latin square design. Three diets were formulated to meet AA requirement estimates based on total AA (Diettotal), apparent ileal digestible AA (DietAID), or standardized ileal digestible AA (DietSID) with constant amounts of corn, soybean meal, and corn germ meal but different crystalline AA contents. Total feces and urine were collected. Nitrogen balance was calculated based on the analyzed data of the diets, feces, and urine samples. Preplanned orthogonal contrasts were used to compare the least squares means among treatments: 1) Diettotal vs. DietAID and DietSID and 2) DietAID vs. DietSID. Pigs fed Diettotal had less retained N (P=0.048) and retention coefficients (P<0.01) resulting in greater urinary (P=0.014) and total (P=0.017) N excretion than DietAID and DietSID. Urinary N excretion tended to be greater (P=0.074) for pigs fed DietAID than DietSID. In conclusion, formulating swine diets based on digestible AA rather than on total AA can reduce N excretion.